ICE CREAM BASICS

THE INGREDIENTS FOR ICE CREAM COULD not be simpler—cream, milk, sugar, flavorings, and sometimes eggs. The results, however, vary greatly, depending on the quantities of each ingredient and the techniques used.

There are two basic types of ice cream. Custard-style ice cream contains egg yolks and has a silky texture and rich flavor. Philadelphia-style ice cream is made without eggs, and often the ingredients are combined without any cooking. It's the difference between a pale yellow French vanilla ice cream and a bright white plain vanilla.

While commercial versions of these two styles abound, we have found that home cooks are better off preparing a custard-type ice cream with egg yolks. These ice creams have the creamy texture we associate with high-quality ice cream. Egg yolks are about 10 percent lecithin, an emulsifier that helps maintain an even dispersal of fat droplets in ice cream and also helps keep ice crystals small. The overall effect is one of richness and smoothness.

Store-bought ice creams made without eggs often contain stabilizers and emulsifiers. Home cooks would not (and generally cannot) add these ingredients to ice cream. Also, commercial ice cream machines are able to inject much more air into Philadelphia-style ice cream than home machines. With more air, these eggless ice creams have a lighter, less icy texture.

Once we decided that custard-style ice creams were the way to go, many other issues arose. How many egg yolks are needed for a one-quart batch of ice cream? What kind of dairy should be used? Cream, half-and-half, milk, or some combination? Also, what's the best way to prepare a custard without causing the eggs to curdle?

We tested as many as eight and as few as three egg yolks in our master recipe. Although five or six eggs deliver an excellent texture, we find the egg flavor becomes too pronounced. Ice cream should taste of dairy, sugar, and flavorings, not like scrambled eggs. Four yolks give ice cream the appropriate silkiness without overpowering other flavors.

The question of which dairy products to use proved more complicated. Ice cream made with all cream is too buttery. The fat content is so high that churning causes tiny particles of butter to form. However, ice cream made with all milk or even half-and-half is too lean. These dairy products contain more water, and the result is an ice cream with tiny ice crystals.

After extensive testing, we came to prefer an equal amount of heavy cream and whole milk. The texture is rich, but there is no butteriness. Most important, there is enough fat to prevent the formation of large ice crystals that might otherwise occur when using a lower-fat dairy combination.

Besides adding sweetness, sugar also promotes a smoother, softer, more "scoopable" end product. This is because sugar reduces the number and size of ice crystals and lowers the freezing temperature of the custard. The latter effect allows you to churn the custard longer before it freezes firm, thus incorporating more air into the ice cream.

In our testing, we found that the texture of a quart of ice cream made with one cup of sugar is excellent, but the sweetness overpowers delicate flavors like vanilla. We tried one-half cup of sugar per quart of ice cream and found that the ice cream was too firm to scoop right from the freezer. The texture was marred by iciness as well. Three-quarters cup sugar is enough to keep the ice cream soft and smooth without making it cloying. Note that bitter flavors like cocoa need to be offset with additional sugar.

With the ingredient issues settled, we turned our focus to questions of technique. We soon discovered that subtle changes in the custard-making process can have a profound effect on texture. Our goal was absolute smoothness and creaminess. Of course, the danger of heating the eggs too high and causing the custard to curdle (the eggs literally clump together, as in making scrambled eggs, and cause the custard to break and become lumpy) also lurks in the background.

Our test kitchen came up with the following list of tips that will guarantee optimum texture and prevent curdling.

PREHEAT MILK AND CREAM WITH SOME SUGAR. We like to heat the milk, cream, and part of the sugar to 175 degrees. Do not heat this mixture any higher, or you may curdle the eggs when you add the mixture to them. Lower temperatures will not dissolve the sugar fully and thus are also not advised.

BEAT YOLKS AND SOME SUGAR. While the milk, cream, and part of the sugar are heating, beat the yolks with the remaining sugar. When making vanilla ice cream, we found that adding unbeaten or lightly beaten yolks to the custard results in an ice cream with a shocking yellow color. Even though color is not an issue in all ice creams (chocolate, for example), we found that prolonged beating—at least two minutes with an electric mixer set to medium-high or four minutes with a whisk—helps dissolve the sugar and evenly disperses the emulsifying agent contained in the yolks. This maximizes the thickening and emulsifying power of the eggs once they are added to the custard.

TEMPER BEATEN YOLKS SLOWLY. Sudden exposure to high heat can curdle eggs and should be avoided. Thus, add a small portion of the hot milk-cream mixture to the beaten eggs in a slow stream, whisking constantly as you pour. Use a towel to hold the bowl containing the yolks in place. This process, called tempering, also thins out the thick yolk-sugar mixture so that it can be more easily incorporated into the hot milk and cream.

HEAT CUSTARD SLOWLY. Whisk the thinned yolks back into the pan with the remaining hot milk and cream. Start heating the custard slowly, and never allow it to boil or it will become lumpy. We found that heating the custard slowly (as opposed to quickly) results in a smoother, thicker texture. Also, you are less likely to curdle a custard set over low heat. Depending on your stove and other variables, plan on at least three minutes, and ideally five to ten minutes, to heat the custard to the proper temperature.

TEMPERATURE IS KEY FOR PERFECT CUSTARD. We found that various "tricks" for determining when a custard is fully cooked are only minimally helpful. Yes, a custard does thicken enough to coat the back of a spoon. Yes, a custard should hold its shape when a line is drawn through it on the back of the spoon. But these things may happen well before the custard has reached 180 degrees, the temperature we find ideal for ice cream making. Since egg yolks start to curdle between 185 and 190 degrees, our recommended final temperature of 180 degrees provides some margin of error but allows the eggs to provide a maximum amount of thickening. A custard cooked to only 160 or 170 degrees will make a slightly less rich, less silky ice cream. For this reason, we advocate the use of an instant-read thermometer when making custard for ice cream.

STRAIN CUSTARD FOR BETTER TEXTURE. No matter how careful you are, tiny bits of egg may overcook and form thin particles or strands, especially around the edges and bottom of the pan. Pouring the cooked custard through a fine-mesh strainer will eliminate any of these solid egg pieces. However, a curdled custard with large clumps of eggs cannot be rescued and should be discarded.

CHILL, CHILL, CHILL. It's imperative that you chill the custard fully before placing it in an ice cream machine. We found that chilling the custard to 40 degrees or lower is ideal. We also found that if the custard is too warm when it is placed in the ice cream machine, it will need to be churned for much longer (up to an hour) until frozen to a semisolid state. Ice cream machines with canisters that require freezing before churning will loose their cooling ability before this stage is reached. Ice cream machines with self-contained freezers can bring warm custards down to the correct temperature, but the extra churning causes the formation of butter flecks.

DO NOT CHURN TOO LONG. Ice cream will not emerge from any ice cream maker (including those that cost $500) with a firm texture. Once the ice cream is well chilled (about 25 degrees), fluffy, and frozen to the texture of soft-serve ice cream, remove it from the ice cream maker. It takes about thirty minutes of churning to reach this stage in most ice cream machines. If you churn any longer, you may promote the development of butter flecks. In any case, further churning will not freeze ice cream any harder. Several hours in the freezer will complete the freezing process.

WAIT FOR ADD-INS. Nuts, chocolate, raisins, cookies, and other small items should be added to ice cream just before the churning is completed. We generally add them right to the ice cream maker and allow it to churn for another thirty seconds to distribute them. If you allow the ice cream maker to churn any longer, the blade will start to smash and eventually pulverize your add-in ingredients.

STORE IN AIRTIGHT CONTAINER. Once the ice cream has been churned to the consistency of soft ice cream, turn off the ice cream machine and transfer the ice cream to a nonreactive container. We like plastic containers with airtight lids. Ideally, we prefer to put the ice cream in the freezer for two to four hours before serving. It will emerge soft and silky. Homemade ice cream can be frozen for up to two days. If kept longer, homemade ice cream becomes icy and loses much of its flavor.

WARM BEFORE SERVING. If you store ice cream for more than a few hours, the texture will become firm, like that of the ice cream sold in supermarket freezer cases. If you prefer a softer texture, transfer the container with the ice cream to the refrigerator thirty minutes to one hour before serving. We find that ice cream tastes best around 10 to 12 degrees.