Greek-style thickened yogurts are a change of pace from standard yogurt. If you know how to make traditional yogurt at home, you can make thick yogurt as well, without adding specialty thickeners. Some commercial brands add cornstarch and other thickeners to yogurt to mimic the texture of traditional Greek yogurt, but these additives can alter yogurt's "mouthfeel" -- how it feels in your mouth. Once you understand the food science behind yogurt, you can use that knowledge to change its texture, whether you start with store-bought yogurt or yogurt you make at home.
Strain Out the Whey
The simplest way to make thick yogurt is also the most traditional. Typical yogurt, whether it's store-bought or homemade, holds a significant amount of liquid, or whey, suspended in the solids. Set a colander in your sink or a large bowl, then line it with cheesecloth. Pour in homemade or store-bought plain yogurt. Fold the cheesecloth over the yogurt; then cover it with a small plate to weigh it down. The weight will press extra moisture, or whey, out of the yogurt, leaving the thickened solids behind. This process can take anywhere from a few minutes to several hours, depending on how thick you like your yogurt. If you plan to let it strain for more than two hours, set the colander inside a bowl to catch the whey and refrigerate it to prevent spoilage.
Add More Protein
If you make yogurt from scratch at home, you can alter the ingredients to achieve the texture you want. Protein is what makes yogurt thicken during the fermentation process. As the milk heats up, milk proteins coagulate, causing the solids to separate from the liquids. Adding nonfat dry milk powder to your milk before you make the yogurt results in thicker yogurt because the dry milk adds protein without adding extra liquid.
Increase the Heat
Holding the milk at 200 degrees Fahrenheit for 20 minutes or longer evaporates some of the liquid, concentrating the milk proteins that eventually become yogurt. Because you are using less liquid at the beginning, the resulting yogurt is naturally thicker. Use a candy thermometer and watch the milk carefully during this process. It's very easy to scald, or burn, the milk at this stage, which ruins your yogurt.
Increase Fermentation Time
Increasing the fermentation time, or the time you allow your yogurt to set, results in thicker yogurt. It also gives the yogurt cultures more time to make acid, which gives the yogurt its characteristic tang. If you leave it too long, the yogurt goes from pleasantly tangy to downright sour. The key to this technique is balancing texture and flavor. If you want to eat the yogurt plain, you may not like it as tangy. However, if you plan to flavor it with sweet fillings such as fruit purees or jam, a little extra sourness may not be a problem.
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