How to fix a sauce with overheated yogurt that has separated?

Did it and rescued it - important extended family meal and I took a curds and whey disaster to a great sauce! I cooked up chicken with its yoghurt base marinade, the yoghurt split. It tastes fine it's just the proteins have changed at high heat and clumped to form curds.

To solve it I:

1. took a small amount of water (2 tablespoons or so) in a jug and mixed in a couple of teaspoons of cornstarch. I then added this to the sauce. Don't add cornstarch directly or it will just lump.
2. OPTIONAL: take other sauce ingredients that are meant to be whole (tomatoes in my case) and add 1/2 to sauce
3. blend to a smooth sauce using stick mixer (careful of hot sauce splashes)
4. Reduce sauce, if necessary, to thicken sauce on a medium heat stirring frequently
5. Return chicken to sauce and add the rest of the ingredients.

Serve and eat, and not to self "next time you cook with yoghurt do it slowly on a low heat - DO NOT BOIL"

Once the proteins in the yogurt have curdled, you are unlikely to ever get it back to a truly smooth consistency. This is far more likely with low-fat yogurts, which have proportionately more proteins.

This is different from a broken emulsion (such as a hollandaise), where the fats and water in the sauce separate—these can be repaired under some circumstances. Unfortunately, when the cause of the breaking is curdled proteins, once the proteins tighten up, it is essentially irreversible. What you have are little bits of fresh yogurt cheese suspended in the sauce.

Of course, it is still perfectly safe to eat, even if it doesn't look as good as you would like.

In the future, you can mitigate the chance of the sauce breaking by using a full-fat yogurt—you might have to get this from an ethnic market, depending on where you live. Recipes with lower acid are also less likely to curdle, although you haven't mentioned the full recipe you used.

Add teaspoon or two of flour to the yogurt before adding to the sauce will greatly reduce the chance of curdling. Also add the yogurt at the end of cooking and keep it no higher than a bare simmer. Adding yogurt slowly helps too. Also use the higher fat yogurt. A dash of cream added before the yogurt goes in will help. Starch and fat reduce the chance of the clumping of the solids in the yogurt thus lessening the chance of curdling. Once curdled it is hard to fix. However, whisking the sauce to beat up the curds, add some cream and flour can effectively hide the curdle and get it to the point of being acceptable.

You can't re-integrate once yogurt is split for the reasons @SAJ14SAJ has said, the only thing you can do is to try and break the curds up as small as possible by using a blender. This will destroy any texture you have in the dish, so it may not be a workable solution for you.

I've had this happen to me many times, especially using low or non-fat yogurt. It's really hard to keep non-fat from splitting, even by using the methods below, so stick with low-fat:

1. Reduce the heat before adding yogurt. Adding your yogurt while the dish is cool, then heating it back up again slowly will help reduce the chances of yogurt separating
2. Add it in a spoon at a time. Adding it all at once will almost certainly make it separate

Using method 1 alone takes too long if you're on a time budget, what I do is turn off the heat, then after 30 seconds or so I add the yogurt in a spoon at a time, then put the heat back on. I've found that method is the fastest way to get yogurt into a dish.

I just had this happen to me when making an alfredo sauce, but I managed to fix it! I had TRIED to go gentle, adding some hot milk to the yogurt and thinning it first, then adding it 1/4 by 1/4 into the larger pot. When it still separated, I turned the heat off immediately.

Then, in a pot on the side, I made a basic bechamel sauce (no onions, herbs, etc - just roux and milk) and stirred it into the separated alfredo sauce, turning the heat on as low as it could go. Once it was stirred in, somehow I think the bechamel absorbed the whey or something (I am no cooking chemist, I just go by instinct). Anyhow - it worked! And it may work for you too :)

It can help to puree the sauce with peeled, cooked potato. Thickens the sauce and hides the separated dairy bits. Any non-fibrous cooked veg in your stew can be incorporated into the puree, further thickening and masking the problem. Sweet potatoes, carrots, and peeled tomatoes work well, for example.

Take the dish off the heat and let cool for 5 min then take about 1/2 - 1 cup of the sauce out and add the yoghurt slowly , mix well then slowly put back in to your dish then slowly bring back to serving temp.