What causes yogurt in sauces to split? How to prevent it? A lot of my favorite curry recipes have a yogurt based sauce in them, but on a pretty regular basis when I make them, the yogurt ends up splitting into basically curds and whey. What causes that, and how can I prevent it?

As an illustrative example, last night I made a simple tofu curry as follows:


warm evoo in a pan
add chopped onion, saute briefly
add curry seasonings, allow to warm/season the oil
add cubed tofu, toss to coat
cook for a while, tossing periodically to lightly brown the cubes
turn heat off
add plain greek yogurt
stir to combine


In the few minutes it took to finish the rest of the meal and start plating, the yogurt had separated so I had a clumpy, lumpy, yogurt soup instead of a smooth creamy sauce.
Yogurt is a mesh of denatured milk protein that traps the whey.

When yogurt is over-heated those proteins tighten and squeeze out the extra whey. When the protein matrix is cut it will also leak whey.

To combat this add a little starch. A little cornstarch mixed into the yogurt will prevent the yogurt proteins from over-coagulating. All heated yogurt sauces that I have seen include starch for this reason.

I should also add that this problem occurs mostly with lowfat yogurt. Extra milk fat in yogurt will interfere with the protein's ability to coagulate the same way the starch does.