Fat-Free Dairy Products

I've heard that adding cornstarch to fat-free dairy products will help stabilize them during cooking. Is that true? And how much should I add? —J.O., Newbury, Vermont

Fat-free dairy products, such as fat-free half-and-half or fat-free milk, can be used with great success to replace high-fat cream in many recipes. However, they can be a little tricky to work with. If you've made sauces, soups or gravies with any kind of cream or milk, you know that curdling can occur as the mixture is heated up. This is even more likely to happen, and to a greater degree, when you are using a low-fat or fat-free product. That's because the lack of fat allows proteins to coagulate, or clump together, to form a curdled look. Cornstarch or flour can act to block the proteins in fat-free dairy products and keep them from coagulating. They also help thicken the sauce or gravy, making the texture seem creamier, as when you use full-fat dairy products. In our Test Kitchen, we generally add 2 tablespoons of flour or 1 tablespoon of cornstarch for each cup of fat-free dairy product to help stabilize the mixture. You may use more or less, depending on the thickness or "creaminess" desired. For best results, try mixing a small amount of cornstarch or flour into the fat-free milk or cream before it is added to the rest of the ingredients. Or try adding the milk or cream at the last possible minute and cooking over a gentle heat (much as you would with a full-fat dairy product). We have had the most success with lightening up sauces and gravies when a small amount of fat, such as butter or oil, or even an egg yolk, is added to help coat the particles of flour or cornstarch …and enhance the thickening process.