You may not have realized it, but cheesecakes are just custards that happen to be made with cream cheese instead of milk. And like custards, there are two major categories of cheesecake—those with starch and those without. Adding starch to cheesecakes, or to any custard, affects both the cooking method and the texture, making it firmer and less likely to curdle or weep.
Without starch, cheesecakes are creamy
The texture of a cheesecake without starch is quite smooth and, if the batter contains sour cream, it’s also incredibly creamy: a sensuous, luxurious combination that’s perfect for a rich dessert cheesecake (see the recipes Classic Creamy Cheesecake and Pumpkin Cheesecake with Gingersnap & Pecan Crust).
Without starch, cheesecakes rely on eggs for their thickening power. Thickening occurs when raw egg proteins unwind and link together, which is what happens when eggs cook. Also, emulsifiers in the egg yolk—lecithin and lipoproteins—help give the cheesecake a smooth texture.
Like other custards without starch, cheesecakes need gentle heat to prevent curdling. A little heat cooks the proteins just enough to make them loosely link together to form a thick but smooth texture; but beyond a certain heat threshold, the proteins tighten up and form curds. As with crème anglaise (a boiled custard), which must be stirred constantly over very low heat, a cheesecake without starch must be baked very gently and evenly to avoid curdling.
There are several ways to shield a cheesecake without starch against too much heat. Betsy Murrelle, a cookware shop owner in Banner Elk, North Carolina (and an outstanding cook), bakes her cheesecakes in a 275°F oven for one hour, and then leaves them in the turned-off oven for another hour. My friend Doris Koplin, a professional baker and cheesecake expert, bakes her cheesecake without starch at 350°F for 30-minutes (just enough time to get the batter hot) and then she turns off the heat and leaves the cheesecake in the closed oven for about an hour to continue cooking very slowly.
Another method is to bake the cheesecake in a water bath. In a 350°F oven, the temperature in a water bath will hover around 200°F, which allows the custard to set without curdling.
Cheesecakes with starch set up firm
When you add cornstarch or flour to cheesecake, the texture becomes firmer and coarser—maybe not ideal for a dessert, but I find it quite appropriate for a savory cheesecake. The thickening occurs when the granules of starch are heated, which causes them to swell and eventually pop, releasing their contents and creating a tangled network of molecules.
Starch in the batter affects the method of cooking. Just as crème pâtissière (pastry cream), which is essentially a crème anglaise plus starch, can be cooked over direct medium-low heat without curdling, so can a cheesecake with starch be cooked without a water bath in a moderately hot oven. In this case, the starch protects the eggs from scrambling by preventing egg coagulation. How? I lean toward a theory that swollen starch granules physically “get in the way” of the linking egg proteins, thereby slowing down coagulation. Whatever the mechanism, the presence of starch means you can safely cook cheesecake at 325°F for up to an hour without a water bath, just as you can bring crème pâtissière to a boil without fear of curdling.
Why cheesecakes crack
The question I’m asked most frequently about cheesecakes is “Why did my cheesecake crack?” It’s difficult for cooks to believe my answer: it’s overcooked. “That can’t be,” the cook protests. “The center jiggled a tiny bit, as if it weren’t done.” That’s true when the cake is hot, but examine it after chilling and you’ll see that it’s firm and dry right around the crack. Overcooking causes proteins to shrink and the cake to dry out, leading to-cracks.
I think that judging cheesecake doneness is one of the most deceptive and disconcerting things in cooking. I’ve made Rose Levy Beranbaum’s cheesecakes successfully many times, and every time there’s a section in the center, at least three inches in diameter, that wobbles wildly as if it were totally runny inside. I’m always amazed that after chilling, the cake is perfectly cooked.
The simplest way to avoid cracks is to shorten the cooking time, but you also can play with other variables. Sugar slows cooking by blocking the coagulation of proteins, so adding more provides an extra barrier against overcooking. Another option is to cut an egg out of the recipe. Fewer eggs means fewer proteins, a slower rate of coagulation, and slower cooking.
If the unmentionable does occur and you end up with minor fissures in the cake, do what my baker friend Doris does: ice the cake with whipped cream, and no one will ever know the difference.