Name-brand standard (0.3) (0.3).

6760 6760

Economy standard (0.3) (0.3).

64 64.

"French" (commercial) 2 2.

6758 6758

French (handmade) 68 68 6954 6954

Gelato 48 48 5550 5550

Soft-serve (0.4) (0.4).

7360 7360

Low-fat (0.8) (0.8).

6861 6861

Sherbet (0.5) (0.5).

7259 7259

Kulfi - - 7060 7060

Style Overrun (% volume Overrun (% volume of original mix)

Calories per c/125 ml Calories per c/125 ml

Premium standard 2040 2040 240360 240360

Name-brand standard 6090 6090 130250 130250

Economy standard 90100 90100 120150 120150

"French" (commercial) 6090 6090 130250 130250

French (handmade) 020 020 150270 150270

Gelato 010 010 300370 300370

Soft-serve 3060 3060 175190 175190

Low-fat 7590 7590 80135 80135

Sherbet 2550 2550 95140 95140

Kulfi 020 020 170230 170230

Making Ice Cream There are three basic steps in making ice cream: preparing the mix, freezing it, and hardening it. There are three basic steps in making ice cream: preparing the mix, freezing it, and hardening it.

Preparing the Mix The first step is to choose the ingredients and combine them. The basic ingredients are fresh cream and milk and table sugar. A mix made of up to 17% milk fat (equal volumes of whole milk and heavy cream) and 15% table sugar ( cup per quart/180 gm per liter of liquid) will be smooth when frozen quickly in kitchen ice cream makers. A smooth but lower-fat ice cream can be made by making a custard-style mix with egg yolks; or by replacing some of the cream with high protein evaporated, condensed, or powdered milk; or replacing some of the sugar with thickening corn syrup. The first step is to choose the ingredients and combine them. The basic ingredients are fresh cream and milk and table sugar. A mix made of up to 17% milk fat (equal volumes of whole milk and heavy cream) and 15% table sugar ( cup per quart/180 gm per liter of liquid) will be smooth when frozen quickly in kitchen ice cream makers. A smooth but lower-fat ice cream can be made by making a custard-style mix with egg yolks; or by replacing some of the cream with high protein evaporated, condensed, or powdered milk; or replacing some of the sugar with thickening corn syrup.

In commercial practice, most or all of the mix ingredients are combined, then pasteurized, a step that also helps dissolve and hydrate the ingredients. If carried out at a high enough temperature (above 170F/76C), cooking can improve the body and smoothness of the ice cream by denaturing the whey proteins, which helps minimize the size of the ice crystals. Mixes that include egg yolks are always cooked until they just thicken. Simple home mixtures of cream and sugar can be frozen uncooked and have their own fresh flavor.

Freezing Once the mix has been prepared, it's prechilled to speed the subsequent freezing. It's then frozen as rapidly as possible in a container with coolant-chilled walls. The mix is stirred to expose it evenly to the cold walls, to incorporate some air, and above all to produce a smooth texture. Slow cooling of an unstirred mix - "quiescent cooling" - causes the formation of relatively few ice crystals that grow to a large size, grow together into clumps, and give a coa.r.s.e, icy texture. Rapid cooling with stirring causes the quick production of many "seed" crystals which, because they share the available water molecules among themselves, cannot grow as large as a smaller population could; the agitation also helps prevent several crystals from growing into each other and forming a cl.u.s.ter that the tongue might notice. And many small crystals give a smooth, velvety consistency. Once the mix has been prepared, it's prechilled to speed the subsequent freezing. It's then frozen as rapidly as possible in a container with coolant-chilled walls. The mix is stirred to expose it evenly to the cold walls, to incorporate some air, and above all to produce a smooth texture. Slow cooling of an unstirred mix - "quiescent cooling" - causes the formation of relatively few ice crystals that grow to a large size, grow together into clumps, and give a coa.r.s.e, icy texture. Rapid cooling with stirring causes the quick production of many "seed" crystals which, because they share the available water molecules among themselves, cannot grow as large as a smaller population could; the agitation also helps prevent several crystals from growing into each other and forming a cl.u.s.ter that the tongue might notice. And many small crystals give a smooth, velvety consistency.

Freezing Ice Cream with Flying Fortresses and Liquid NitrogenOn March 13, 1943, the New York Times New York Times reported that American fliers stationed in Britain had discovered an ingenious way of making ice cream while on duty. A story t.i.tled "Flying Fortresses Double as Ice-Cream Freezers" disclosed that the airmen "place prepared ice-cream mixture in a large can and anchor it to the rear gunner's compartment of a Flying Fortress. It is well shaken up and nicely frozen by flying over enemy territory at high alt.i.tudes." reported that American fliers stationed in Britain had discovered an ingenious way of making ice cream while on duty. A story t.i.tled "Flying Fortresses Double as Ice-Cream Freezers" disclosed that the airmen "place prepared ice-cream mixture in a large can and anchor it to the rear gunner's compartment of a Flying Fortress. It is well shaken up and nicely frozen by flying over enemy territory at high alt.i.tudes."These days, a popular, spectacular, and effective method among chemistry teachers is to freeze the mix in an open bowl with a gallon or two/810 liters of liquid nitrogen, whose boiling point is320F/196C. When the liquid nitrogen is stirred in, it boils, bubbles, and chills the mix almost instantly throughout, a combination that makes a very smooth - and initially very cold! - ice cream.

Hardening Hardening is the last stage in making ice cream. When the mix becomes thick and difficult to stir, only about half of its water has frozen into ice crystals. Agitation is then stopped, and the ice cream is finished with a period of quiescent freezing, during which another 40% of its water migrates onto existing ice crystals, leaving the various solid components less lubricated. If hardening is slow, some ice crystals take up more water than others and coa.r.s.en the texture. Hardening can be accelerated by dividing the newly frozen ice cream into several small containers whose greater surface area will release heat faster than one large container. Hardening is the last stage in making ice cream. When the mix becomes thick and difficult to stir, only about half of its water has frozen into ice crystals. Agitation is then stopped, and the ice cream is finished with a period of quiescent freezing, during which another 40% of its water migrates onto existing ice crystals, leaving the various solid components less lubricated. If hardening is slow, some ice crystals take up more water than others and coa.r.s.en the texture. Hardening can be accelerated by dividing the newly frozen ice cream into several small containers whose greater surface area will release heat faster than one large container.

Storing and Serving Ice Cream Ice cream is best stored as cold as possible, at 0F/18C or below, to preserve its smoothness. The inevitable coa.r.s.ening during storage is due to repeated partial thawings and freezings, which melt the smallest ice crystals completely and deposit their water molecules on ever fewer, ever larger crystals. The lower the storage temperature, the slower this coa.r.s.ening process. Ice cream is best stored as cold as possible, at 0F/18C or below, to preserve its smoothness. The inevitable coa.r.s.ening during storage is due to repeated partial thawings and freezings, which melt the smallest ice crystals completely and deposit their water molecules on ever fewer, ever larger crystals. The lower the storage temperature, the slower this coa.r.s.ening process.

The ice cream surface suffers in two ways during storage: its fat absorbs odors from the rest of the freezer compartment, and can be damaged and go rancid when dried out by the freezer air. These problems can be prevented simply by pressing plastic wrap directly into the surface, being careful not to leave air pockets.

Ideally, ice cream should be allowed to warm up from 0F before being served. At 810F/13C, it doesn't numb the tongue and taste buds as much, and it contains more liquid water, which softens the texture. At 22F/6C - the typical temperature of soft-serve ice cream - half of the water is in liquid form.

Fresh Fermented Milks and Creams One of the remarkable qualities of milk is that it invites its own preservation. It can spontaneously foster a particular group of microbes that convert its sugar into acid, and thereby preserve it for some time from spoiling or harboring disease. At the same time, the microbes also change the milk's texture and flavor in desirable ways. This benign transformation, or fermentation, fermentation, doesn't happen all the time, but it happened often enough that milks fermented by bacteria became important among all dairying peoples. Yogurt and soured creams remain widely popular to this day. doesn't happen all the time, but it happened often enough that milks fermented by bacteria became important among all dairying peoples. Yogurt and soured creams remain widely popular to this day.

Why this fortunate fermentation? It's a combination of milk's unique chemistry, and a group of microbes that were ready to exploit this chemistry long before mammals and milk arrived on earth. The lactic acid bacteria lactic acid bacteria are what make possible the variety of fermented dairy products. are what make possible the variety of fermented dairy products.

Lactic Acid Bacteria Milk is rich in nutrients, but its most readily tapped energy source, lactose, is a sugar found almost nowhere else in nature. This means that not many microbes have the necessary digestive enzymes at the ready. The elegantly simple key to the success of the milk bacteria is that they specialize in digesting lactose, and they extract energy from lactose by breaking it down to lactic acid. Then they release the lactic acid into the milk, where it acc.u.mulates and r.e.t.a.r.ds the growth of most other microbes, including those that cause human disease. They also make some antibacterial substances, but their main defense is a pleasantly puckery tartness, one that also causes the casein proteins to gather together in semisolid curds (p. 20) and thicken the milk.

There are two major groups of lactic acid bacteria. The small genus Lactococcus Lactococcus (a combination of the Latin for "milk" and "sphere") is found primarily on plants (but it's a close relative of (a combination of the Latin for "milk" and "sphere") is found primarily on plants (but it's a close relative of Streptococcus, Streptococcus, whose members live mainly on animals and cause a number of human diseases!). The 50-odd members of the genus whose members live mainly on animals and cause a number of human diseases!). The 50-odd members of the genus Lactobacillus Lactobacillus ("milk" and "rod") are more widespread in nature. They're found both on plants and in animals, including the stomach of milk-fed calves and the human mouth, digestive tract, and v.a.g.i.n.a; and their clean living generally benefits our insides (see box, p. 47). ("milk" and "rod") are more widespread in nature. They're found both on plants and in animals, including the stomach of milk-fed calves and the human mouth, digestive tract, and v.a.g.i.n.a; and their clean living generally benefits our insides (see box, p. 47).

The bacteria responsible for the major fermented products were identified around 1900, and pure cultures of individual strains became available then. Nowadays, few dairies leave their fermentations to chance. Where traditional spontaneously fermented products may involve a dozen or more different microbes, the industrial versions are usually limited to two or three. This biological narrowing may affect flavor, consistency, and health value.

Families of Fresh Fermented Milks Unlike most cheeses (p. 51), which undergo several stages of manipulation and continue to evolve for weeks or months, fresh fermented milks are usually finished and ready for eating within hours or days. A recent encyclopedia catalogued several hundred different kinds! Most of them originated in western Asia, eastern Europe, and Scandinavia, and have been carried across the globe by countless emigrants, many of whom dipped a cloth in their family's culture, dried it gently, and guarded it until they could moisten it in the milk of their new home.

The handful of fresh fermented milks familiar in the West, yogurt and soured creams and b.u.t.termilk, represent two major families that developed from the dairying habits of peoples in two very different climates.

Yogurt and its relatives are native to a broad and climatically warm area of central and southwest Asia and the Middle East, an area that includes the probable home of dairying, and where some peoples still store milk in animal stomachs and skins. The lactobacilli and streptococci that produce yogurt are "thermophilic," or heat-loving species that may have come from the cattle themselves. They're distinguished by their ability to grow rapidly and synergistically at temperatures up to 113F/45C, and to generate high levels of preservative lactic acid. They can set milk into a very tart gel in just two or three hours. and its relatives are native to a broad and climatically warm area of central and southwest Asia and the Middle East, an area that includes the probable home of dairying, and where some peoples still store milk in animal stomachs and skins. The lactobacilli and streptococci that produce yogurt are "thermophilic," or heat-loving species that may have come from the cattle themselves. They're distinguished by their ability to grow rapidly and synergistically at temperatures up to 113F/45C, and to generate high levels of preservative lactic acid. They can set milk into a very tart gel in just two or three hours.

The curdling of milk by lactic acid bacteria. As the bacteria ferment lactose and produce lactic acid, the increasingly acid conditions cause the normal bundled micelles of casein proteins (left) (left) to fall apart into separate casein molecules, and then rebond to each other to fall apart into separate casein molecules, and then rebond to each other (right). (right). This general rebonding forms a continuous meshwork of protein molecules that traps the liquid and fat globules in small pockets, and turns the fluid milk into a fragile solid. This general rebonding forms a continuous meshwork of protein molecules that traps the liquid and fat globules in small pockets, and turns the fluid milk into a fragile solid.

Traditional Fresh Fermented Milks and Creams Product

Region Region

Yogurt

Middle East to India Middle East to India

b.u.t.termilk

Eurasia Eurasia

Creme fraiche

Europe Europe

Sour cream

Europe Europe

Ropy milks

Scandinavia Scandinavia

Koumiss

Central Asia Central Asia

Kefir

Central Asia Central Asia