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Cutting Out Curdling in Cultured Dairy

By Cook's Illustrated Published September 2011

The cultured dairy products in some of our favorite recipes are sensitive to heat and can easily curdle if the stew is too hot or reheated. We wondered if another dairy product would provide a more stable tang.

Dishes like beef stroganoff, chicken paprikash, and many of the Moroccan stews known as tagines wouldn’t be complete without a little sour cream or yogurt stirred in at the end. However, these cultured dairy products are sensitive to heat and can easily curdle if the stew is too hot or reheated. We wondered if another dairy product would provide a more stable tang. 

Experiment

We stirred dollops of whole-milk yogurt, full-fat sour cream, and crème fraîche (which boasts much more fat) into water that we brought to just a simmer (185 degrees). After letting the samples sit for 10 seconds, we examined the liquid for signs of curdling. 

Results

Both the yogurt and the sour cream mixtures quickly curdled, while the crème fraîche mixture remained perfectly creamy.

Explanation

Curdling occurs when excessive heat causes the whey proteins in dairy to denature (unfold) and bind with casein proteins, forming clumps of larger proteins. The greater amount of butterfat in crème fraîche (30 to 40 percent, versus 18 to 20 percent and roughly 4 percent in sour cream and yogurt, respectively) protects against this process by more thoroughly coating the proteins and preventing them from binding together. Plus, with more fat, crème fraîche has far fewer proteins to bind together in the first place. It’s now our go-to dairy product for hot dishes; in fact, we found that crème fraîche is so resistant to curdling that it can withstand reheating.

SOUR CREAM

Curdled

YOGURT

Curdled

CREME FRAICHE

Creamy