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Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Virtually all of the ice on Earth is of a hexagonal crystalline structure denoted as ice I_h (spoken as “ice one h”). Depending on temperature and pressure, at least nineteen phases (packing geometries) can exist. The most common phase transition to ice I_h occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. When water is cooled rapidly (quenching), up to three types of amorphous ice can form. Interstellar ice is overwhelmingly low-density amorphous ice (LDA), which likely makes LDA ice the most abundant type in the universe. When cooled slowly, correlated proton tunneling occurs below −253.15 °C (20 K, −423.67 °F) giving rise to macroscopic quantum phenomena.

Ice is abundant on the Earth’s surface, particularly in the polar regions and above the snow line, where it can aggregate from snow to form glaciers and ice sheets. As snowflakes and hail, ice is a common form of precipitation, and it may also be deposited directly by water vapor as frost. The transition from ice to water is melting and from ice directly to water vapor is sublimation. These processes plays a key role in Earth’s water cycle and climate. In the recent decades, ice volume on Earth has been decreasing due to climate change. The largest declines have occurred in the Arctic and in the mountains located outside of the polar regions. The loss of grounded ice (as opposed to floating sea ice) is the primary contributor to sea level rise.

Humans have been using ice for various purposes for thousands of years. Some historic structures designed to hold ice to provide cooling are over 2,000 years old. Before the invention of refrigeration technology, the only way to safely store food without modifying it through preservatives was to use ice. Sufficiently solid surface ice makes waterways accessible to land transport during winter, and dedicated ice roads may be maintained. Ice also plays a major role in winter sports.

Physical properties

Further information: Water (properties) § Density of water and ice

Ice possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms; while it is a weak bond, it is nonetheless critical in controlling the structure of both water and ice.^[6]

An unusual property of water is that its solid form—ice frozen at atmospheric pressure—is approximately 8.3% less dense than its liquid form; this is equivalent to a volumetric expansion of 9%. The density of ice is 0.9167^[1]–0.9168^[2] g/cm³ at 0 °C and standard atmospheric pressure (101,325 Pa), whereas water has a density of 0.9998^[1]–0.999863^[2] g/cm³ at the same temperature and pressure. Liquid water is densest, essentially 1.00 g/cm³, at 4 °C and begins to lose its density as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. The density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).^[7]

When water freezes, it increases in volume (about 9% for fresh water).^[8] The effect of expansion during freezing can be dramatic, and ice expansion is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes.^[9]

Because ice is less dense than liquid water, it floats, and this prevents bottom-up freezing of the bodies of water. Instead, a sheltered environment for animal and plant life is formed beneath the floating ice, which protects the underside from short-term weather extremes such as wind chill. Sufficiently thin floating ice allows light to pass through, supporting the photosynthesis of bacterial and algal colonies.^[10] When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids. In turn, they provide food for animals such as krill and specialized fish like the bald notothen, fed upon in turn by larger animals such as emperor penguins and minke whales.^[11]

When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C (176 °F).^[12] During the melting process, the temperature remains constant at 0 °C (32 °F). While melting, any energy added breaks the hydrogen bonds between ice (water) molecules. Energy becomes available to increase the thermal energy (temperature) only after enough hydrogen bonds are broken that the ice can be considered liquid water. The amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.^[12][8]

As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen–hydrogen (O–H) bond stretch. Compared with water, this absorption is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice.^[13] Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities (e.g., sediments, algae, air bubbles) can appear brown, grey or green.^[13]

Because ice in natural environments is usually close to its melting temperature, its hardness shows pronounced temperature variations. At its melting point, ice has a Mohs hardness of 2 or less, but the hardness increases to about 4 at a temperature of −44 °C (−47 °F) and to 6 at a temperature of −78.5 °C (−109.3 °F), the vaporization point of solid carbon dioxide (dry ice).^[14]

Phases

Main article: Phases of ice

Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than 1 atm (0.10 MPa), water freezes at a temperature below 0 °C (32 °F). Ice, water, and water vapour can coexist at the triple point, which is exactly 273.16 K (0.01 °C) at a pressure of 611.657 Pa.^[16][17] The kelvin was defined as ⁠1/273.16⁠ of the difference between this triple point and absolute zero,^[18] though this definition changed in May 2019.^[19] Unlike most other solids, ice is difficult to superheat. In an experiment, ice at −3 °C was superheated to about 17 °C for about 250 picoseconds.^[20]

Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases at various densities, along with hypothetical proposed phases of ice that have not been observed.^[21] With care, at least fifteen of these phases (one of the known exceptions being ice X) can be recovered at ambient pressure and low temperature in metastable form.^[22][23] The types are differentiated by their crystalline structure, proton ordering,^[24] and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Ice XII was discovered in 1996. In 2006, Ice XIII and Ice XIV were discovered.^[25] Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I_h, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143 °C.^[26] At even higher pressures, ice is predicted to become a metal; this has been variously estimated to occur at 1.55 TPa^[27] or 5.62 TPa.^[28]

As well as crystalline forms, solid water can exist in amorphous states as amorphous solid water (ASW) of varying densities. In outer space, hexagonal crystalline ice is present in the ice volcanoes,^[29] but is extremely rare otherwise. Even icy moons like Ganymede are expected to mainly consist of other crystalline forms of ice.^[30][31] Water in the interstellar medium is dominated by amorphous ice, making it likely the most common form of water in the universe.^[32] Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for noctilucent clouds on Earth and is usually formed by deposition of water vapor in cold or vacuum conditions.^[33] High-density ASW (HDA) is formed by compression of ordinary ice I_h or LDA at GPa pressures. Very-high-density ASW (VHDA) is HDA slightly warmed to 160 K under 1–2 GPa pressures.^[34]

Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of 500,000 bars (7,300,000 psi) such superionic ice would take on a body-centered cubic structure. However, at pressures in excess of 1,000,000 bars (15,000,000 psi) the structure may shift to a more stable face-centered cubic lattice. It is speculated that superionic ice could compose the interior of ice giants such as Uranus and Neptune.^[35]

Friction properties

Ice is “slippery” because it has a low coefficient of friction. This subject was first scientifically investigated in the 19th century. The preferred explanation at the time was “pressure melting” -i.e. the blade of an ice skate, upon exerting pressure on the ice, would melt a thin layer, providing sufficient lubrication for the blade to glide across the ice.^[36] Yet, 1939 research by Frank P. Bowden and T. P. Hughes found that skaters would experience a lot more friction than they actually do if it were the only explanation. Further, the optimum temperature for figure skating is −5.5 °C (22 °F; 268 K) and −9 °C (16 °F; 264 K) for hockey; yet, according to pressure melting theory, skating below −4 °C (25 °F; 269 K) would be outright impossible.^[37] Instead, Bowden and Hughes argued that heating and melting of the ice layer is caused by friction. However, this theory does not sufficiently explain why ice is slippery when standing still even at below-zero temperatures.^[36]

Subsequent research suggested that ice molecules at the interface cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semi-liquid state, providing lubrication regardless of pressure against the ice exerted by any object. However, the significance of this hypothesis is disputed by experiments showing a high coefficient of friction for ice using atomic force microscopy.^[37] Thus, the mechanism controlling the frictional properties of ice is still an active area of scientific study.^[38] A comprehensive theory of ice friction must take into account all of the aforementioned mechanisms to estimate friction coefficient of ice against various materials as a function of temperature and sliding speed. 2014 research suggests that frictional heating is the most important process under most typical conditions.^[39]

Natural formation

The term that collectively describes all of the parts of the Earth’s surface where water is in frozen form is the cryosphere. Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt is an important source of seasonal fresh water.^[42][43] The World Meteorological Organization defines several kinds of ice depending on origin, size, shape, influence and so on.^[44] Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice.^[45][46]

In the oceans

Main article: Sea ice

Ice that is found at sea may be in the form of drift ice floating in the water, fast ice fixed to a shoreline or anchor ice if attached to the seafloor.^[47] Ice which calves (breaks off) from an ice shelf or a coastal glacier may become an iceberg.^[48] The aftermath of calving events produces a loose mixture of snow and ice known as Ice mélange.^[49]

Sea ice forms in several stages. At first, small, millimeter-scale crystals accumulate on the water surface in what is known as frazil ice. As they become somewhat larger and more consistent in shape and cover, the water surface begins to look “oily” from above, so this stage is called grease ice.^[50] Then, ice continues to clump together, and solidify into flat cohesive pieces known as ice floes. Ice floes are the basic building blocks of sea ice cover, and their horizontal size (defined as half of their diameter) varies dramatically, with the smallest measured in centimeters and the largest in hundreds of kilometers.^[51] An area which is over 70% ice on its surface is said to be covered by pack ice.^[52]

Fully formed sea ice can be forced together by currents and winds to form pressure ridges up to 12 metres (39 ft) tall.^[53] On the other hand, active wave activity can reduce sea ice to small, regularly shaped pieces, known as pancake ice.^[54] Sometimes, wind and wave activity “polishes” sea ice to perfectly spherical pieces known as ice eggs.^[55][56]

• Grease ice in the Bering Sea
• Loose drift ice on the east coast of Greenland
• Ice eggs (diameter 5–10 cm) on Stroomi Beach, Tallinn, Estonia
• Ice floes in Antarctica, 1919
• A first-year sea ice ridge in the Central Arctic, photographed by the MOSAiC expedition on July 4, 2020
• Ice mélange on Greenland’s western coast, 2012
• Anchor ice on the seafloor at McMurdo Sound, Antarctica.

On land

The largest ice formations on Earth are the two ice sheets which almost completely cover the world’s largest island, Greenland, and the continent of Antarctica. These ice sheets have an average thickness of over 1 km (0.6 mi) and have existed for millions of years.^[57][58]

Other major ice formations on land include ice caps, ice fields, ice streams and glaciers. In particular, the Hindu Kush region is known as the Earth’s “Third Pole” due to the large number of glaciers it contains. They cover an area of around 80,000 km² (31,000 sq mi), and have a combined volume of between 3,000-4,700 km³.^[42] These glaciers are nicknamed “Asian water towers”, because their meltwater run-off feeds into rivers which provide water for an estimated two billion people.^[43]

Permafrost refers to soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more.^[59] The ice within permafrost is divided into four categories: pore ice, vein ice (also known as ice wedges), buried surface ice and intrasedimental ice (from the freezing of underground waters).^[60] One example of ice formation in permafrost areas is aufeis – layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.^[61] Snow line and snow fields are two related concepts, in that snow fields accumulate on top of and ablate away to the equilibrium point (the snow line) in an ice deposit.^[62]

On rivers and streams

Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. Ice jams (sometimes called “ice dams”), when broken chunks of ice pile up, are the greatest ice hazard on rivers. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Ice jams can cause some hydropower industrial facilities to completely shut down. An ice dam is a blockage from the movement of a glacier which may produce a proglacial lake. Heavy ice flows in rivers can also damage vessels and require the use of an icebreaker vessel to keep navigation possible.^[63][64]

Ice discs are circular formations of ice floating on river water. They form within eddy currents, and their position results in asymmetric melting, which makes them continuously rotate at a low speed.^[65][66]

On lakes

Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: primary, secondary, superimposed and agglomerate.^[67][68] Primary ice forms first. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow. Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in the ice which often settles when loaded with snow. An ice shove occurs when ice movement, caused by ice expansion and/or wind action, occurs to the extent that ice pushes onto the shores of lakes, often displacing sediment that makes up the shoreline.^[69]

Shelf ice is formed when floating pieces of ice are driven by the wind piling up on the windward shore. This kind of ice may contain large air pockets under a thin surface layer, which makes it particularly hazardous to walk across it.^[70] Another dangerous form of rotten ice to traverse on foot is candle ice, which develops in columns perpendicular to the surface of a lake. Because it lacks a firm horizontal structure, a person who has fallen through has nothing to hold onto to pull themselves out.^[71]

As precipitation

Main article: Precipitation

Snow and freezing rain

Main articles: Snow and Snowflake

Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than −18 °C (255 K; 0 °F), because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this “nucleus”. Experiments show that this “homogeneous” nucleation of cloud droplets only occurs at temperatures lower than −35 °C (238 K; −31 °F).^[72] In warmer clouds an aerosol particle or “ice nucleus” must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor – what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,^[73] although to what extent is unclear. Artificial nuclei are used in cloud seeding.^[74] The droplet then grows by condensation of water vapor onto the ice surfaces.^[75]

Ice storm is a type of winter storm characterized by freezing rain, which produces a glaze of ice on surfaces, including roads and power lines. In the United States, a quarter of winter weather events produce glaze ice, and utilities need to be prepared to minimize damages.^[76]

Hard forms

Further information: Ice crystal

Hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei, such as dust or dirt. The storm’s updraft blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more.^[77] Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in) and GS for smaller.^[78] Stones of 19 millimetres (0.75 in), 25 millimetres (1.0 in) and 44 millimetres (1.75 in) are the most frequently reported hail sizes in North America.^[79] Hailstones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb).^[80] In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo ‘wet growth’, where the liquid outer shell collects other smaller hailstones.^[81] The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm’s updraft, it falls from the cloud.^[82]

Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).^[77] Hail-producing clouds are often identifiable by their green coloration.^[83][84] The growth rate is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).^[85] Entrainment of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporative cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.^[86]

Ice pellets (METAR code PL^[78]) are a form of precipitation consisting of small, translucent balls of ice, which are usually smaller than hailstones.^[87] This form of precipitation is also referred to as “sleet” by the United States National Weather Service.^[88] (In British English “sleet” refers to a mixture of rain and snow.) Ice pellets typically form alongside freezing rain, when a wet warm front ends up between colder and drier atmospheric layers. There, raindrops would both freeze and shrink in size due to evaporative cooling.^[89] So-called snow pellets, or graupel, form when multiple water droplets freeze onto snowflakes until a soft ball-like shape is formed.^[90] So-called “diamond dust“, (METAR code IC^[78]) also known as ice needles or ice crystals, forms at temperatures approaching −40 °C (−40 °F) due to air with slightly higher moisture from aloft mixing with colder, surface-based air.^[91]

On surfaces

As water drips and re-freezes, it can form hanging icicles, or stalagmite-like structures on the ground.^[92] On sloped roofs, buildup of ice can produce an ice dam, which stops melt water from draining properly and potentially leads to damaging leaks.^[93] More generally, water vapor depositing onto surfaces due to high relative humidity and then freezing results in various forms of atmospheric icing, or frost. Inside buildings, this can be seen as ice on the surface of un-insulated windows.^[94] Hoar frost is common in the environment, particularly in the low-lying areas such as valleys.^[95] In Antarctica, the temperatures can be so low that electrostatic attraction is increased to the point hoarfrost on snow sticks together when blown by wind into tumbleweed-like balls known as yukimarimo.^[96]

Sometimes, drops of water crystallize on cold objects as rime instead of glaze. Soft rime has a density between a quarter and two thirds that of pure ice,^[97] due to a high proportion of trapped air, which also makes soft rime appear white. Hard rime is denser, more transparent, and more likely to appear on ships and aircraft.^[98][99] Cold wind specifically causes what is known as advection frost when it collides with objects. When it occurs on plants, it often causes damage to them.^[100] Various methods exist to protect agricultural crops from frost – from simply covering them to using wind machines.^[101][102] In recent decades, irrigation sprinklers have been calibrated to spray just enough water to preemptively create a layer of ice that would form slowly and so avoid a sudden temperature shock to the plant, and not be so thick as to cause damage with its weight.^[101]

• Grass partially covered in hoarfrost, 2008
• Frost on a thistle in Hausdülmen, North Rhine-Westphalia, Germany
• A spiderweb covered in frost
• Ice on deciduous tree after freezing rain
• Icicles on a stairway in Seattle, 1968
• Fern frost on a window
• Hoar frost atop snow
• Yukimarimo at South Pole Station, Antarctica, in 2008

Ablation

Main article: Ablation

Ablation of ice refers to both its melting and its dissolution.^[103]

The melting of ice entails the breaking of hydrogen bonds between the water molecules. The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become a liquid. This is achieved by increasing the internal energy of the ice beyond the melting point. When ice melts it absorbs as much energy as would be required to heat an equivalent amount of water by 80 °C. While melting, the temperature of the ice surface remains constant at 0 °C. The rate of the melting process depends on the efficiency of the energy exchange process. An ice surface in fresh water melts solely by free convection with a rate that depends linearly on the water temperature, T_∞, when T_∞ is less than 3.98 °C, and superlinearly when T_∞ is equal to or greater than 3.98 °C, with the rate being proportional to (T_∞ − 3.98 °C)^α, with α = ⁠5/3⁠ for T_∞ much greater than 8 °C, and α = ⁠4/3⁠ for in between temperatures T_∞.^[104]

In salty ambient conditions, dissolution rather than melting often causes the ablation of ice. For example, the temperature of the Arctic Ocean is generally below the melting point of ablating sea ice. The phase transition from solid to liquid is achieved by mixing salt and water molecules, similar to the dissolution of sugar in water, even though the water temperature is far below the melting point of the sugar. However, the dissolution rate is limited by salt concentration and is therefore slower than melting.^[105]

Role in human activities

Cooling

Ice has long been valued as a means of cooling. In 400 BC Iran, Persian engineers had already developed techniques for ice storage in the desert through the summer months. During the winter, ice was transported from harvesting pools and nearby mountains in large quantities to be stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). Yakhchals were large underground spaces (up to 5000 m³) that had thick walls (at least two meters at the base) made of a specific type of mortar called sarooj made from sand, clay, egg whites, lime, goat hair, and ash. The mortar was resistant to heat transfer, helping to keep the ice cool enough not to melt; it was also impenetrable by water. Yakhchals often included a qanat and a system of windcatchers that could lower internal temperatures to frigid levels, even during the heat of the summer. One use for the ice was to create chilled treats for royalty.^[106][107]

Harvesting

Main articles: Ice cutting and Ice trade

There were thriving industries in 16th–17th century England whereby low-lying areas along the Thames Estuary were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was allegedly copied by an Englishman who had seen the same activity in China. Ice was imported into England from Norway on a considerable scale as early as 1823.^[108]

In the United States, the first cargo of ice was sent from New York City to Charleston, South Carolina, in 1799,^[108] and by the first half of the 19th century, ice harvesting had become a big business. Frederic Tudor, who became known as the “Ice King”, worked on developing better insulation products for long distance shipments of ice, especially to the tropics; this became known as the ice trade.^[109]

Between 1812 and 1822, under Lloyd Hesketh Bamford Hesketh‘s instruction, Gwrych Castle was built with 18 large towers, one of those towers is called the ‘Ice Tower’. Its sole purpose was to store Ice.^[110]

Trieste sent ice to Egypt, Corfu, and Zante; Switzerland, to France; and Germany sometimes was supplied from Bavarian lakes.^[108] From 1930s and up until 1994, the Hungarian Parliament building used ice harvested in the winter from Lake Balaton for air conditioning.^[111]

Ice houses were used to store ice formed in the winter, to make ice available all year long, and an early type of refrigerator known as an icebox was cooled using a block of ice placed inside it. Many cities had a regular ice delivery service during the summer. The advent of artificial refrigeration technology made the delivery of ice obsolete.^[112]

Ice is still harvested for ice and snow sculpture events. For example, a swing saw is used to get ice for the Harbin International Ice and Snow Sculpture Festival each year from the frozen surface of the Songhua River.^[113]

Artificial production

Main article: Icemaker

The earliest known written process to artificially make ice is by the 13th-century writings of Arab historian Ibn Abu Usaybia in his book Kitab Uyun al-anba fi tabaqat-al-atibba concerning medicine in which Ibn Abu Usaybia attributes the process to an even older author, Ibn Bakhtawayhi, of whom nothing is known.^[114]

Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.^[115] Most commercial icemakers produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.^[115] Large batch ice makers can produce up to 75 tons of ice per day.^[116] In 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.^[117] Home refrigerators can also make ice with a built in icemaker, which will typically make ice cubes or crushed ice. The first such device was presented in 1965 by Frigidaire.^[118]

Land travel

Ice forming on roads is a common winter hazard, and black ice particularly dangerous because it is very difficult to see. It is both very transparent, and often forms specifically in shaded (and therefore cooler and darker) areas, i.e. beneath overpasses.^[119]

Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Often, snow melts, re-freezes, and forms a fragmented layer of ice which effectively “glues” snow to the window. In this case, the frozen mass is commonly removed with ice scrapers.^[120] A thin layer of ice crystals can also form on the inside surface of car windows during sufficiently cold weather. In the 1970s and 1980s, some vehicles such as Ford Thunderbird could be upgraded with heated windshields as the result. This technology fell out of style as it was too expensive and prone to damage, but rear-window defrosters are cheaper to maintain and so are more widespread.^[121]Duration: 2 minutes and 56 seconds.2:561943 US propaganda film explaining how the ice of Lake Ladoga became the Road of Life during WWII

In sufficiently cold places, the layers of ice on water surfaces can get thick enough for ice roads to be built. Some regulations specify that the minimum safe thickness is 4 in (10 cm) for a person, 7 in (18 cm) for a snowmobile and 15 in (38 cm) for an automobile lighter than 5 tonnes. For trucks, effective thickness varies with load – i.e. a vehicle with 9-ton total weight requires a thickness of 20 in (51 cm). Notably, the speed limit for a vehicle moving at a road which meets its minimum safe thickness is 25 km/h (15 mph), going up to 35 km/h (25 mph) if the road’s thickness is 2 or more times larger than the minimum safe value.^[122] There is a known instance where a railroad has been built on ice.^[123]

The most famous ice road had been the Road of Life across Lake Ladoga. It operated in the winters of 1941–1942 and 1942–1943, when it was the only land route available to the Soviet Union to relieve the Siege of Leningrad by the German Army Group North.^{[124] : 76–80} The trucks moved hundreds of thousands tonnes of supplies into the city, and hundreds of thousands of civilians were evacuated.^[125] It is now a World Heritage Site.^[126]

Water-borne travel

For ships, ice presents two distinct hazards. Firstly, spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, potentially to the point of capsizing.^[127] Earlier, crewmembers were regularly forced to manually hack off ice build-up. After 1980s, spraying de-icing chemicals or melting the ice through hot water/steam hoses became more common.^[128] Secondly, icebergs – large masses of ice floating in water (typically created when glaciers reach the sea) – can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous being the Titanic.^[129]

For harbors near the poles, being ice-free, ideally all year long, is an important advantage. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland), and Vardø (Norway). Harbors which are not ice-free are opened up using specialized vessels, called icebreakers.^[130] Icebreakers are also used to open routes through the sea ice for other vessels, as the only alternative is to find the openings called “polynyas” or “leads“. A widespread production of icebreakers began during the 19th century. Earlier designs simply had reinforced bows in a spoon-like or diagonal shape to effectively crush the ice. Later designs attached a forward propeller underneath the protruding bow, as the typical rear propellers were incapable of effectively steering the ship through the ice ^[130]

Air travel

Further information: Icing conditions and Carburetor icing

For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. In 1919, during the first non-stop flight across the Atlantic, the British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown encountered such icing conditions – Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the Vickers Vimy aircraft they were flying.^[133]

One vulnerability effected by icing that is associated with reciprocating internal combustion engines is the carburetor. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes adiabatic cooling. Thus, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. Between 1969 and 1975, 468 such instances were recorded, causing 75 aircraft losses, 44 fatalities and 202 serious injuries.^[134] Thus, carburetor air intake heaters were developed. Further, reciprocating engines with fuel injection do not require carburetors in the first place.^[135]

Jet engines do not experience carb icing, but they can be affected by the moisture inherently present in jet fuel freezing and forming ice crystals, which can potentially clog up fuel intake to the engine. Fuel heaters and/or de-icing additives are used to address the issue.^[136]

Recreation and sports

Main article: Ice sports

Ice plays a central role in winter recreation and in many sports such as ice skating, tour skating, ice hockey, bandy, ice fishing, ice climbing, curling, broomball and sled racing on bobsled, luge and skeleton. Many of the different sports played on ice get international attention every four years during the Winter Olympic Games.^[137]

Small boat-like craft can be mounted on blades and be driven across the ice by sails. This sport is known as ice yachting, and it had been practiced for centuries.^[138][139] Another vehicular sport is ice racing, where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to dirt track racing). The sport has even been modified for ice rinks.^[140]

Other uses

As thermal ballast

• Ice is still used to cool and preserve food in portable coolers.^[112]
• Ice cubes or crushed ice can be used to cool drinks. As the ice melts, it absorbs heat and keeps the drink near 0 °C (32 °F).^[141]
• Ice can be used as part of an air conditioning system, using battery- or solar-powered fans to blow hot air over the ice. This is especially useful during heat waves when power is out and standard (electrically powered) air conditioners do not work.^[142]
• Ice can be used (like other cold packs) to reduce swelling (by decreasing blood flow) and pain by pressing it against an area of the body.^[143]

As structural material

• Engineers used the substantial strength of pack ice when they constructed Antarctica’s first floating ice pier in 1973.^[144] Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally occurring frozen seawater in McMurdo Sound until the dock reaches a depth of about 22 feet (6.7 m). Ice piers are inherently temporary structures, although some can last as long as 10 years. Once a pier is no longer usable, it is towed to sea with an icebreaker.^[145]

• Structures and ice sculptures are built out of large chunks of ice or by spraying water^[123] The structures are mostly ornamental (as in the case with ice castles), and not practical for long-term habitation. Ice hotels exist on a seasonal basis in a few cold areas.^[146] Igloos are another example of a temporary structure, made primarily from snow.^[147]
• Engineers can also use ice to destroy. In mining, drilling holes in rock structures and then pouring water during cold weather is an accepted alternative to using dynamite, as the rock cracks when the water expands as ice.^[9]
• During World War II, Project Habbakuk was an Allied programme which investigated the use of pykrete (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a vessel immune to torpedoes, and a large deck, could be constructed by ice. A small-scale prototype was built,^[148] but it soon turned out the project would cost far more than a conventional aircraft carrier while being many times slower and also vulnerable to melting.^[149]
• Ice has even been used as the material for a variety of musical instruments, for example by percussionist Terje Isungset.^[150]

Impacts of climate change

See also: Climate change in the Arctic and Climate change in Antarctica

Historical

Greenhouse gas emissions from human activities unbalance the Earth’s energy budget and so cause an accumulation of heat.^[152] About 90% of that heat is added to ocean heat content, 1% is retained in the atmosphere and 3-4% goes to melt major parts of the cryosphere.^[152] Between 1994 and 2017, 28 trillion tonnes of ice were lost around the globe as the result.^[151] Arctic sea ice decline accounted for the single largest loss (7.6 trillion tonnes), followed by the melting of Antarctica’s ice shelves (6.5 trillion tonnes), the retreat of mountain glaciers (6.1 trillion tonnes), the melting of the Greenland ice sheet (3.8 trillion tonnes) and finally the melting of the Antarctic ice sheet (2.5 trillion tonnes) and the limited losses of the sea ice in the Southern Ocean (0.9 trillion tonnes).^[151]

Other than the sea ice (which already displaces water due to Archimedes’ principle), these losses are a major cause of sea level rise (SLR) and they are expected to intensify in the future. In particular, the melting of the West Antarctic ice sheet may accelerate substantially as the floating ice shelves are lost and can no longer buttress the glaciers. This would trigger poorly understood marine ice sheet instability processes, which could then increase the SLR expected for the end of the century (between 30 cm (1 ft) and 1 m (3+¹⁄₂ ft), depending on future warming), by tens of centimeters more.^{[153]: 1302}

Ice loss in Greenland and Antarctica also produces large quantities of fresh meltwater, which disrupts the Atlantic meridional overturning circulation (AMOC) and the Southern Ocean overturning circulation, respectively.^[154] These two halves of the thermohaline circulation are very important for the global climate. A continuation of high meltwater flows may cause a severe disruption (up to a point of a “collapse”) of either circulation, or even both of them. Either event would be considered an example of tipping points in the climate system, because it would be extremely difficult to reverse.^[154] AMOC is generally not expected to collapse during the 21st century, while there is only limited knowledge about the Southern Ocean circulation.^{[153]: 1214}

Another example of ice-related tipping point is permafrost thaw. While the organic content in the permafrost causes CO₂ and methane emissions once it thaws and begins to decompose,^[154] ice melting liqufies the ground, causing anything built above the former permafrost to collapse. By 2050, the economic damages from such infrastructure loss are expected to cost tens of billions of dollars.^[155]

Predictions

In the future, the Arctic Ocean is likely to lose effectively all of its sea ice during at least some Septembers (the end of the ice melting season), although some of the ice would refreeze during the winter. I.e. an ice-free September is likely to occur once in every 40 years if global warming is at 1.5 °C (2.7 °F), but would occur once in every 8 years at 2 °C (3.6 °F) and once in every 1.5 years at 3 °C (5.4 °F).^[157] This would affect the regional and global climate due to the ice-albedo feedback. Because ice is highly reflective of solar energy, persistent sea ice cover lowers local temperatures. Once that ice cover melts, the darker ocean waters begin to absorb more heat, which also helps to melt the remaining ice.^[160]

Global losses of sea ice between 1992 and 2018, almost all of them in the Arctic, have already had the same impact as 10% of greenhouse gas emissions over the same period.^[161] If all the Arctic sea ice was gone every year between June and September (polar day, when the Sun is constantly shining), temperatures in the Arctic would increase by over 1.5 °C (2.7 °F), while the global temperatures would increase by around 0.19 °C (0.34 °F).^[156]

By 2100, at least a quarter of mountain glaciers outside of Greenland and Antarctica would melt,^[163] and effectively all ice caps on non-polar mountains are likely to be lost around 200 years after global warming reaches 2 °C (3.6 °F).^[158][159] The West Antarctic ice sheet is highly vulnerable and will likely disappear even if the warming does not progress further,^{[164][165][166][167]} although it could take around 2,000 years before its loss is complete.^[158][159] The Greenland ice sheet will most likely be lost with the sustained warming between 1.7 °C (3.1 °F) and 2.3 °C (4.1 °F),^[168] although its total loss requires around 10,000 years.^[158][159] Finally, the East Antarctic ice sheet will take at least 10,000 years to melt entirely, which requires a warming of between 5 °C (9.0 °F) and 10 °C (18 °F).^[158][159]

If all the ice on Earth melted, it would result in about 70 m (229 ft 8 in) of sea level rise,^[169] with some 53.3 m (174 ft 10 in) coming from East Antarctica.^[58] Due to isostatic rebound, the ice-free land would eventually become 301 m (987 ft 6 in) higher in Greenland and 494 m (1,620 ft 9 in) in Antarctica, on average. Areas in the center of each landmass would become up to 783 m (2,568 ft 11 in) and 936 m (3,070 ft 10 in) higher, respectively.^[170] The impact on global temperatures from losing West Antartica, mountain glaciers and the Greenland ice sheet is estimated at 0.05 °C (0.090 °F), 0.08 °C (0.14 °F) and 0.13 °C (0.23 °F), respectively,^[156] while the lack of the East Antarctic ice sheet would increase the temperatures by 0.6 °C (1.1 °F).^[158][159]

Non-water

Main article: Volatile (astrogeology)

The solid phases of several other volatile substances are also referred to as ices; generally a volatile is classed as an ice if its melting or sublimation point lies above or around 100 K (−173 °C; −280 °F) (assuming standard atmospheric pressure). The best known example is dry ice, the solid form of carbon dioxide. Its sublimation/deposition point occurs at 194.7 K (−78.5 °C; −109.2 °F).^[171]

A “magnetic analogue” of ice is also realized in some insulating magnetic materials in which the magnetic moments mimic the position of protons in water ice and obey energetic constraints similar to the Bernal-Fowler ice rules arising from the geometrical frustration of the proton configuration in water ice. These materials are called spin ice.^[172]

Ice cream is a frozen dessert typically made from milk or cream that has been flavoured with a sweetener, either sugar or an alternative, and a spice, such as cocoa or vanilla, or with fruit, such as strawberries or peaches. Food colouring is sometimes added in addition to stabilizers. The mixture is cooled below the freezing point of water and stirred to incorporate air spaces and prevent detectable ice crystals from forming. It can also be made by whisking a flavoured cream base and liquid nitrogen together. The result is a smooth, semi-solid foam that is solid at very low temperatures (below 2 °C or 35 °F). It becomes more malleable as its temperature increases.

Ice cream may be served in dishes, eaten with a spoon, or licked from edible wafer ice cream cones held by the hands as finger food. Ice cream may be served with other desserts—such as cake or pie—or used as an ingredient in cold dishes—like ice cream floats, sundaes, milkshakes, and ice cream cakes—or in baked items such as Baked Alaska.

Italian ice cream is gelato. Frozen custard is a type of rich ice cream. Soft serve is softer and is often served at amusement parks and fast-food restaurants in the United States. Ice creams made from cow’s milk alternatives, such as goat’s or sheep’s milk, or milk substitutes (e.g., soy, oat, cashew, coconut, almond milk, or tofu), are available for those who are lactose intolerant, allergic to dairy protein, or vegan. Banana “nice cream”^[a] is a 100% fruit-based vegan alternative. Frozen yoghurt, or “froyo”, is similar to ice cream but uses yoghurt and can be lower in fat. Fruity sorbets or sherbets are not ice creams but are often available in ice cream shops.

The meaning of the name ice cream varies from one country to another. In some countries, such as the United States and the United Kingdom,^[1][2] ice cream applies only to a specific variety, and most governments regulate the commercial use of the various terms according to the relative quantities of the main ingredients, notably the amount of cream.^[3] Products that do not meet the criteria to be called ice cream are sometimes labelled “frozen dairy dessert” instead.^[4] In other countries, such as Italy and Argentina, one word is used for all variants.

History

Early frozen desserts

The origins of frozen desserts are obscure, although several accounts exist about their history. Some sources say the history of ice cream begins in Persia in 550 BC.^[5][6][7]

A Roman cookbook dating back to the 1st century includes recipes for sweet desserts that are sprinkled with snow,^[8] and there are Persian records from the 2nd century for sweetened drinks chilled with ice.^[8]

Kakigōri is a Japanese dessert made with ice and flavoured syrup. The origins of kakigōri date back to the Heian period in Japanese history, when blocks of ice saved during the colder months would be shaved and served with sweet syrup to the Japanese aristocracy during the summer.^[9] Kakigōri‘s origin is referred to in The Pillow Book, a book of observations written by Sei Shōnagon, who served the Imperial Court during the Heian period.^[10][11]

The earliest known written process to artificially make ice is known not from culinary texts, but the 13th-century writings of Syrian historian Ibn Abu Usaybia in his book “Kitab Uyun al-anba fi tabaqat-al-atibba“ (Book of Sources of Information on the Classes of Physicians) concerning medicine in which Ibn Abu Usaybi’a attributes the process to an even older author, Ibn Bakhtawayhi, of whom nothing is known.^[12]

Ice cream production became easier with the discovery of the endothermic effect.^[13] Prior to this, cream could be chilled easily but not frozen. The addition of salt lowered the melting point of ice, drawing heat from the cream and allowing it to freeze.

Early modern

In the 16th century, the Mughal Empire used relays of horsemen to bring ice from the Hindu Kush to its capital, Delhi, used to create kulfi, a popular frozen dairy dessert from the Indian subcontinent often described as traditional Indian ice cream.^{[14][better source needed]}

Europe

The technique of freezing was not known from any European sources prior to the 16th century.^[13] During the 16th century, authors made reference to the refrigerant effect that happened when salt was added to ice. By the latter part of the 17th century sorbets and ice creams were made using this process.^[15]

Ice cream’s spread throughout Europe is sometimes attributed to Moorish traders, but more often Marco Polo. Though it is not mentioned in any of his writings, Polo is often credited with introducing sorbet-style desserts to Italy after learning of them during his travels to China.^[16] According to a legend, the Italian duchess Catherine de’ Medici introduced flavoured sorbet ices to France when she brought Italian chefs with her to France upon marrying the Duke of Orléans (Henry II of France) in 1533.^[17][18] No Italian chefs were present in France during the Medici period,^[19] and ice cream already existed in France before de Medici was born.^[20] One hundred years later, Charles I of England was reportedly so impressed by the “frozen snow” that he offered his own ice cream maker a lifetime pension in return for keeping the formula secret, so that ice cream could be a royal prerogative.^[21] There is no evidence to support these legends.^[16][8]

France

In 1665, the Catalogue des Marchandises rares…, edited in Montpellier by Jean Fargeon,^[22] listed a type of frozen sorbet. While the composition of this sorbet is not provided, Fargeon specified that it was consumed frozen using a container that was plunged into a mixture of ice and saltpetre. These sorbets were transported in pots made of clay and sold for three livres per pound.

According to L’Isle des Hermaphrodites,^[23] the practice of cooling drinks with ice and snow had already emerged in Paris, particularly in the court, during the 16th century. The narrator notes that his hosts stored ice and snow, which they later added to their wine. This practice slowly progressed during the reign of Louis XIII and was likely a necessary step towards the creation of ice cream.^[24] In 1682, Le Nouveau confiturier françois provided a recipe for a specific type of ice cream, called “neige de fleur d’orange”.^[20]

In 1686, Italian Francesco dei Coltelli opened an ice cream café in Paris, and the product became so popular that during the next 50 years, another 250 cafés opened in Paris.^[25][26]

The first recipe in French for flavoured ices appears in 1674, in Nicholas Lemery‘s Recueil de curiositéz rares et nouvelles de plus admirables effets de la nature.^[17] Recipes for sorbetti saw publication in the 1694 edition of Antonio Latini’s Lo Scalco alla Moderna (The Modern Steward).^[17] Recipes for flavoured ices begin to appear in François Massialot’s Nouvelle Instruction pour les Confitures, les Liqueurs, et les Fruits, starting with the 1692 edition. Massialot’s recipes result in a coarse, pebbly texture. Latini claims that the results of his recipes should have the fine consistency of sugar and snow.^[17]

England

The first recorded mention of ice cream in England was in 1671. Elias Ashmole described the dishes served at the Feast of St George at Windsor for Charles II in 1671 and included “one plate of ice cream”.^[27] The only table at the banquet with ice cream on it was that of the King.^[28] The first recipe for ice cream in English was published in Mrs. Mary Eales’s Receipts, a book dedicated to confectionary, in London in 1718:^{[29][30][31][27]}

To ice cream.

Take Tin Ice-Pots, fill them with any Sort of Cream you like, either plain or sweeten’d, or Fruit in it; shut your Pots very close; to six Pots you must allow eighteen or twenty Pound of Ice, breaking the Ice very small; there will be some great Pieces, which lay at the Bottom and Top: You must have a Pail, and lay some Straw at the Bottom; then lay in your Ice, and put in amongst it a Pound of Bay-Salt; set in your Pots of Cream, and lay Ice and Salt between every Pot, that they may not touch; but the Ice must lie round them on every Side; lay a good deal of Ice on the Top, cover the Pail with Straw, set it in a Cellar where no Sun or Light comes, it will be froze in four Hours, but it may stand longer; then take it out just as you use it; hold it in your Hand and it will slip out. When you wou’d freeze any Sort of Fruit, either Cherries, Raspberries, Currants, or Strawberries, fill your Tin-Pots with the Fruit, but as hollow as you can; put to them Lemmonade, made with Spring-Water and Lemmon-Juice sweeten’d; put enough in the Pots to make the Fruit hang together, and put them in Ice as you do Cream.

— Mrs. Mary Eale’s Receipts (1718)

The 1751 edition of The Art of Cookery made Plain and Easy by Hannah Glasse includes a recipe for ice cream: “H. GLASSE Art of Cookery (ed. 4) 333 (heading) To make Ice Cream…set it [the cream] into the larger Bason. Fill it with Ice, and a Handful of Salt.”^[32] L’Art de Bien Faire les Glaces d’Office by M. Emy, in 1768, was a cookbook devoted to recipes for flavoured ices and ice cream.^[17]

In 1769 Domenico Negri, an Italian confectioner, founded a business in Berkeley Square London which would become famous for its ice creams.^[33] His shop was at the Sign of the Pineapple (an emblem used by confectioners) and his trade card said he sold “All Sorts of English, French and Italian wet and dry’d Sweet Meats, Cedrati and Bergamot Chips, Naples Diavoloni, All sorts of Baskets & Cakes, fine and Common Sugar plums”, but most importantly, “all Sorts of Ice, Fruits and creams in the best Italian manner.”^[33]

In 1789 Frederick Nutt, who served an apprenticeship at Negri’s establishment, first published The Complete Confectioner. The book had 31 recipes for ice creams, some with fresh fruit, others with jams, and some using fruit syrups. Flavours included ginger, chocolate, brown breadcrumbs and one flavoured with Parmesan cheese.^[33][34]

North America

An early North American reference to ice cream is from 1744: “Among the rarities […] was some fine ice cream, which, with the strawberries and milk, eat most deliciously.”^[35][32] It was served by the lady of Governor Bland.^{[citation needed]}

Who brought ice cream to the United States first is unknown.^[36] Confectioners sold ice cream at their shops in New York and other cities during the colonial era. Benjamin Franklin, George Washington, and Thomas Jefferson were known to have regularly eaten and served ice cream. Records, kept by a merchant from Chatham street, New York, show George Washington spending approximately $200 on ice cream in the summer of 1790. The same records show president Thomas Jefferson having an 18-step recipe for ice cream.^[37] Although it is incorrect that Jefferson introduced ice cream to America, as is popularly believed, he did help to introduce vanilla ice cream.^[38][39] First Lady Dolley Madison, wife of U.S. President James Madison, served ice cream at her husband’s Inaugural Ball in 1813.^[40]

Small-scale hand-cranked ice cream freezers were invented in England by Agnes Marshall and in America by Nancy Johnson in the 1840s.^[41]

Expansion in popularity

In the Mediterranean, ice cream appears to have been accessible to ordinary people by the mid-18th century.^[42] Ice cream became popular and inexpensive in England in the mid-19th century, when Swiss émigré Carlo Gatti set up the first stand outside Charing Cross station in 1851. He sold scoops in shells for one penny. Prior to this, ice cream was an expensive treat confined to those with access to an ice house.^[43] Gatti built an ‘ice well’ to store ice that he cut from Regent’s Canal under a contract with the Regent’s Canal Company. By 1860, he expanded the business and began importing ice on a large scale from Norway.

In New Zealand, a newspaper advertisement for ice cream appeared in 1866, claiming to be the first time ice cream was available in Wellington.^[44] Commercial manufacturing was underway in 1875.^[45] Ice cream rapidly gained in popularity in New Zealand throughout the 20th century.^[46] By 2018, exported ice cream products included new flavours such as matcha to cater to Asian markets.^[47]

Agnes Marshall, regarded as the “queen of ices” in England, did much to popularize ice cream recipes and make its consumption into a fashionable middle-class pursuit. She wrote four books: The Book of Ices (1885), Mrs. A.B. Marshall’s Book of Cookery (1888), Mrs. A.B. Marshall’s Larger Cookery Book of Extra Recipes (1891) and Fancy Ices (1894) and gave public lectures on cooking. She even suggested using liquid nitrogen to make ice cream.

Ice cream soda was invented in the 1870s, adding to ice cream’s popularity. The invention of this cold treat is attributed to American Robert Green in 1874, although there is no conclusive evidence to prove his claim. The ice cream sundae originated in the late 19th century. Some sources say that the sundae was invented to circumvent blue laws, which forbade serving sodas on Sunday. Towns claiming to be the birthplace of the sundae include Buffalo, Two Rivers, Ithaca, and Evanston. Both the ice cream cone and banana split became popular in the early 20th century.^{[citation needed]}

The first mention of the cone being used as an edible receptacle for the ice cream is in Mrs. A.B. Marshall’s Book of Cookery of 1888. Her recipe for “Cornet with Cream” said that “the cornets were made with almonds and baked in the oven, not pressed between irons”.^[48][49] The ice cream cone was popularized in the US at the 1904 World’s Fair in St. Louis, Missouri.^[48]

The history of ice cream in the 20th century is one of great change and increases in availability and popularity. In the United States in the early 20th century, the ice cream soda was a popular treat at the soda shop, the soda fountain, and the ice cream parlour. During the American Prohibition, the soda fountain to some extent replaced the outlawed alcohol establishments such as bars and saloons.

Ice cream became popular throughout the world in the second half of the 20th century after cheap refrigeration became common. There was an explosion of ice cream stores and of flavours and types. Vendors often competed on the basis of variety: Howard Johnson’s restaurants advertised “a world of 28 flavors”, and Baskin-Robbins made its 31 flavours (“one for every day of the month”) the cornerstone of its marketing strategy (the company now boasts that it has developed over 1,000 varieties).

One important development in the 20th century was the introduction of soft ice cream, which has more air mixed in, thereby reducing costs. The soft ice cream machine fills a cone or dish from a spigot. In the United States, chains such as Dairy Queen, Carvel, and Tastee-Freez helped popularize soft-serve ice cream. Baskin-Robbins later incorporated it into their menu.

Technological innovations such as these have introduced various food additives into ice cream, most notably the stabilizing agent gluten,^[50] to which some people have an intolerance. Recent awareness of this issue has prompted a number of manufacturers to start producing gluten-free ice cream.^[51]

The 1980s saw thicker ice creams being sold as “premium” and “super-premium” varieties under brands such as Ben & Jerry’s, Chocolate Shoppe Ice Cream Company and Häagen-Dazs.

Composition

Ice cream is a colloidal emulsion made with water, ice, milk fat, milk protein, sugar and air.^[52][53] Water and fat have the highest proportions by weight creating an emulsion that has dispersed phase as fat globules. The emulsion is turned into foam by incorporating air cells which are frozen to form dispersed ice cells. The triacylglycerols in fat are nonpolar and will adhere to themselves by Van der Waals interactions. Water is polar, thus emulsifiers are needed for dispersion of fat. Also, ice cream has a colloidal phase of foam which helps in its light texture. Milk proteins such as casein and whey protein present in ice cream are amphiphilic, can adsorb water and form micelles which will contribute to its consistency. The proteins contribute to the emulsification, aeration and texture. Sucrose, which is a disaccharide, is usually used as a sweetening agent. Lactose, which is sugar present in milk, will cause freezing point depression. Thus, on freezing some water will remain unfrozen and will not give a hard texture.^[54] Too much lactose will result in a non-ideal texture because of either excessive freezing point depression or lactose crystallization.^[55]

Production

Before the development of modern refrigeration, ice cream was a luxury reserved for special occasions. Making it was quite laborious; ice was cut from lakes and ponds during the winter and stored in holes in the ground, or in wood-frame or brick ice houses, insulated by straw. Many farmers and plantation owners, including US Presidents George Washington and Thomas Jefferson, cut and stored ice in the winter for use in the summer. Frederic Tudor of Boston turned ice harvesting and shipping into a business, cutting ice in New England and shipping it around the world.

Ice cream was made by hand in a large bowl placed inside a tub filled with ice and salt. This is called the pot-freezer method.^[56] French confectioners refined the pot-freezer method, making ice cream in a sorbetière [fr] (a covered pail with a handle attached to the lid). In the pot-freezer method, the temperature of the ingredients is reduced by the mixture of crushed ice and salt. The salt water is cooled by the ice, and the action of the salt on the ice causes it to (partially) melt, absorbing latent heat and bringing the mixture below the freezing point of pure water.

The hand-cranked churn, which also uses ice and salt for cooling, replaced the pot-freezer method. The exact origin of the hand-cranked freezer is unknown, but the first US patent for one was #3254 issued to Nancy Johnson on 9 September 1843. The hand-cranked churn produced smoother ice cream than the pot freezer and did it quicker. Many inventors patented improvements on Johnson’s design.

In Europe and America, ice cream was made and sold by small businesses, mostly confectioners and caterers. Jacob Fussell of Baltimore, Maryland was the first to manufacture ice cream on a large scale. Fussell bought fresh dairy products from farmers in York County, Pennsylvania, and sold them in Baltimore. An unstable demand for his dairy products often left him with a surplus of cream, which he made into ice cream. He built his first ice cream factory in Seven Valleys, Pennsylvania, in 1851. Two years later, he moved his factory to Baltimore. Later, he opened factories in several other cities and taught the business to others, who operated their own plants. Mass production reduced the cost of ice cream and added to its popularity.

The development of industrial refrigeration by German engineer Carl von Linde during the 1870s eliminated the need to cut and store natural ice, and, when the freezer was perfected in 1926, commercial mass production of ice cream and the birth of the modern ice cream industry was underway.

In modern times, a common method for producing ice cream at home is to use an ice cream maker, an electrical device that churns the ice cream mixture while cooled inside a household freezer. Some more expensive models have an built-in freezing element. A newer method is to add liquid nitrogen to the mixture while stirring it using a spoon or spatula for a few seconds; a similar technique, advocated by Heston Blumenthal as ideal for home cooks, is to add dry ice to the mixture while stirring for a few minutes.^[57]

An unusual method of making ice cream was done during World War II by American fighter pilots based in the South Pacific. They attached pairs of 5-US-gallon (19 L) cans to their aircraft. The cans were fitted with a small propeller, this was spun by the slipstream and drove a stirrer, which agitated the mixture while the intense cold of high altitude froze it.^[58] B-17 crews in Europe did something similar on their bombing runs as did others.^[59][60]

Retail sales

Ice cream can be mass-produced and thus is widely available in developed parts of the world. Ice cream can be purchased in large cartons (vats and squrounds) from supermarkets and grocery stores, in smaller quantities from ice cream shops, convenience stores, and milk bars, and in individual servings from small carts or vans at public events. In 2015, the US produced nearly 900 million US gallons (3.4×10⁹ L; 750,000,000 imp gal) of ice cream.^[61]

Specialty job

Today, jobs specialize in the selling of ice cream. The title of a person who works in this speciality is often called an ‘ice cream man’, however women also specialize in the selling of ice cream. People in this line of work often sell ice cream on beaches. On beaches, ice cream is either sold by a person who carries a box full of ice cream and is called over by people who want to purchase ice cream, or by a person who drives up to the top of the beach and rings a bell. In the second method, people go up to the top of the beach and purchase ice cream straight from the ice cream seller, who is often in an ice cream van. In Turkey and Australia, ice cream is sometimes sold to beach-goers from small powerboats equipped with chest freezers.

Some ice cream distributors sell ice cream products from travelling refrigerated vans or carts (commonly referred to in the US as “ice cream trucks”), sometimes equipped with speakers playing children’s music or folk melodies (such as “Turkey in the Straw“). The driver of an ice cream van drives throughout neighbourhoods and stops every so often, usually every block. The seller on the ice cream van sells the ice cream through a large window; this window is also where the customer asks for ice cream and pays. Ice cream vans in the United Kingdom make a music box noise rather than actual music.

Ingredients and definitions

Many countries have regulations controlling what can be described as ice cream.

In the United Kingdom, Food Labelling Regulations (1996) set a requirement of at least 5% milk fat and 2.5% milk protein in order to be sold as ice cream within the UK. In rest of the European Union, a trade organization called European Ice Cream Association calls for minimum dairy fat content of 5%.^[62] In 2015, these regulations were relaxed so that containing milk fat or protein was no longer necessary in the UK for a product to be sold as “ice cream”, though at least 5% milk fat is still required for a product to be labeled “dairy ice cream”. After this change, many UK products labelled as “ice cream” substitute milk fat with cheaper alternatives like palm oil, coconut oil, and vegetable fats.^[63]

In the US, the FDA rules state that to be described as “ice cream”, a product must have the following composition:^[64]

• greater than 10% milk fat
• 6 to 10% milk and non-fat milk solids: this component, also known as the milk solids-not-fat or serum solids, contains the proteins (caseins and whey proteins) and carbohydrates (lactose) found in milk

It generally also has:^[65]

• 12 to 16% sweeteners: usually a combination of sucrose and glucose-based corn syrup sweeteners
• 0.2 to 0.5% stabilizers and emulsifiers
• 55 to 64% water, which comes from the milk or other ingredients

These compositions are percentage by weight. Since ice cream can contain as much as half air by volume, these numbers may be reduced by as much as half if cited by volume. In terms of dietary considerations, the percentages by weight are more relevant. Even low-fat products have high caloric content: Ben and Jerry’s No-Fat Vanilla Fudge, for instance, contains 150 calories (630 kJ) per half-cup due to its high sugar content.^[66]

According to the Canadian Food and Drugs Act and Regulations, ice cream in Canada is divided into “ice cream mix” and “ice cream”. Each has a different set of regulations.^[67]

• “Ice cream” must be at least 10 percent milk fat, and must contain at least 180 grams (6.3 oz) of solids per litre. When cocoa, chocolate syrup, fruit, nuts, or confections are added, the percentage of milk fat can be 8 percent.^[68]
• “Ice cream mix” is defined as the pasteurized mix of cream, milk and other milk products that are not yet frozen.^[67] It may contain eggs, artificial or non-artificial flavours, cocoa or chocolate syrup, a food colour, an agent that adjusts the pH level in the mix, salt, a stabilizing agent that does not exceed 0.5% of the ice cream mix, a sequestering agent which preserves the food colour, edible casein that does not exceed 1% of the mix, propylene glycol mono fatty acids in an amount that will not exceed 0.35% of the ice cream mix, and sorbitan tristearate in an amount that will not exceed 0.035% of the mix.^[67] Ice cream mix may not include less than 36% solid components.^[67]

Physical properties

Ice cream is considered a colloidal system. It is composed by ice cream crystals and aggregates, air that does not mix with the ice cream by forming small bubbles in the bulk and partially coalesced fat globules. This dispersed phase made from all the small particles is surrounded by an unfrozen continuous phase composed by sugars, proteins, salts, polysaccharides and water. Their interactions determine the properties of ice cream, whether soft and whippy or hard.^[69]

Ostwald ripening

Ostwald ripening is the explanation for the growth of large crystals at the expense of small ones in the dispersion phase. This process is also called migratory recrystallization. It involves the formation of sharp crystals. Theories about Ostwald recrystallization admit that after a period of time, the recrystallization process can be described by the following equation:

r=r(0)+Rtexp⁡(1/n)

Where r (0) is the initial size, n the order of recrystallization, and t a time constant for recrystallization that depends on the rate R (in units of size/time).

To make ice cream smooth, recrystallization must occur as slowly as possible, because small crystals create smoothness, meaning that r must decrease.^[70]

Food safety concerns

From the perspective of food chemistry, ice cream is a colloid or foam. The dietary emulsifier plays an important role in ice cream. Soy lecithin and polysorbate are two popular emulsifiers used for ice cream production. A mouse study in 2015 shows that two commonly used dietary emulsifiers carboxymethyl cellulose (CMC) and polysorbate 80 (P80) can potentially cause inflammatory bowel diseases, weight gain, and other metabolic syndromes.^[71]

Around the world

Around the world, different cultures have developed unique versions of ice cream, suiting the product to local tastes and preferences.

Overview

Main article: List of ice cream varieties by country

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Italian ice cream, or gelato as it is known, is a traditional and popular dessert in Italy. Much of the production is still hand-made and flavoured by each individual shop in gelaterie a produzione propria. Gelato is made from whole milk, sugar, sometimes eggs, and natural flavourings. It typically contains 7–8% fat, less than ice cream’s minimum of 10%.^{[citation needed]}

Per capita, Australians and New Zealanders are among the leading ice cream consumers in the world, eating 18 litres (4.0 imp gal; 4.8 US gal) and 20 litres (4.4 imp gal; 5.3 US gal) each per year respectively, behind the United States where people eat 23 litres (5.1 imp gal; 6.1 US gal) each per year.^[72]

Golas are summer treat consisting of shaved ice packed into a popsicle form on a stick and soaked in flavoured sugar syrup, a popular choice being kala khatta, made from the sweet and sour jamun fruit.^[73]

In Spain, ice cream is often in the style of Italian gelato. Spanish helado can be found in many cafés or speciality ice cream stores. While many traditional flavours are sold, cafés may also sell flavours like nata, viola, crema catalana, or tiramisu. In the 1980s, the Spanish industry was known for creating many creative and weird ice cream bars.^[74]

In the United Kingdom, 14 million adults buy ice cream as a treat, in a market worth £1.8 billion (according to a report produced in 2024).^[75] In the United States, ice cream made with just cream, sugar, and a flavouring (usually fruit) is sometimes referred to as “Philadelphia style”^[76] ice cream. Ice cream that uses eggs to make a custard is sometimes called “French ice cream”. American federal labelling standards require ice cream to contain a minimum of 10% milk fat. Americans consume about 23 litres of ice cream per person per year—the most in the world. According to the NPD Group, the most popular ice cream flavours in the U.S. are vanilla and chocolate with a combined market share of 40% as of 2008.^[77]

Cones

Main article: Ice cream cone

Mrs A. B. Marshall’s Cookery Book, published in 1888,^[78] endorsed serving ice cream in cones.^[79] Agnes Marshall was a celebrated cookery writer of her day and helped to popularize ice cream. She patented and manufactured an ice cream maker and was the first to suggest using liquefied gases to freeze ice cream after seeing a demonstration at the Royal Institution.

Reliable evidence proves that ice cream cones were served in the 19th century, and their popularity increased greatly during the St. Louis World’s Fair in 1904. According to legend, an ice cream vendor at the fair ran out of cardboard dishes. The vendor at the Syrian waffle booth next door, unsuccessful in the intense heat, offered to make cones by rolling up his waffles. The new product sold well and was widely copied by other vendors.^[49][48]

Cryogenics

In 2006, some commercial ice cream makers began to use liquid nitrogen in the primary freezing of ice cream, thus eliminating the need for a conventional ice cream freezer.^[80] The preparation results in a column of white condensed water vapour cloud. The ice cream, dangerous to eat while still “steaming” with liquid nitrogen, is allowed to rest until the liquid nitrogen is completely vaporized. Sometimes ice cream is frozen to the sides of the container, and must be allowed to thaw. Good results can also be achieved with the more readily available dry ice, and authors such as Heston Blumenthal have published recipes to produce ice cream and sorbet using a simple blender.^[81]