With its natural creaminess and distinctive tang, plain yogurt is a key ingredient for many soups, sauces, and drinks. In India, cooks rely on yogurt for its marvelous ability to marinate meats, keep foods moist during lengthy cooking, make curries creamy, and deliver tangy flavor.
Made from milk that's been fermented and coagulated (thanks to the introduction of good-for-you bacteria), plain yogurt contains no additional sugar or flavorings (though they may contain starch and pectin for texture.) It ranges from full-fat to non-fat. Because low-fat yogurts tend to be more acidic than whole-milk, the two can't necessarily be substituted for each other.
Sour cream or crème fraîche can substitute for yogurt in some recipes, the former in savory preparations, the latter in sweet, though baked goods may be affected due to different acidity levels.
There are many varieties of plain yogurt available, from those made by giant companies to artisanal ones made in small batches to the super thick and rich Greek yogurts. Their tanginess ranges, as does their texture (from rich, thick and billowy to soupy and thin), so sample different brands to see which you prefer.
It's often a good idea to stir yogurt before using it. Most yogurt will curdle over high heat, so gentle heating is your best bet. Greek yogurt, which is strained. has more fat, so it's your best bet when cooking yogurt with high heat. You can also strain plain yogurt in a sieve lined with cheesecloth, a coffee filter, or a plain white paper towel set over a bowl. Refrigerate and allow the liquid to drain off for two hours. One cup of regular yogurt yields about 1/2 cup of thick, Greek-style yogurt.
Keep yogurt refrigerated and use by the date stamped on the package.