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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:

  1. warm evoo in a pan
  2. add chopped onion, saute briefly
  3. add curry seasonings, allow to warm/season the oil
  4. add cubed tofu, toss to coat
  5. cook for a while, tossing periodically to lightly brown the cubes
  6. turn heat off
  7. add plain greek yogurt
  8. 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.

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1  
Fats are not needed in order for something to brown. When you are browning tofu, you are indeed browning the actual tofu. You can discover this for yourself by either grilling tofu or browning it without oil in a nonstick pan. –  daniel May 15 '11 at 21:53
    
It was a coin toss between James's answer and @sobachatina's... both seem to be right on the spot. Letting the curry cool not just removing from the heat, seems to do it best, so I'm accepting James' answer. –  cabbey Sep 7 '11 at 21:42

6 Answers 6

up vote 12 down vote accepted

You are trying to add the yoghurt at too high a temperature. Let the dish cool to around 75 deg C before adding the yoghurt, and make adding the yoghurt the last thing you do before serving.

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Stir a little starch into the yogurt before adding it to the hot dish & it will not split.

The usual ratio is-

2 tsp white flour to 1 cup yogurt

1 tsp corn starch to 1 cup yogurt

1 tsp gram flour to 1 cup yogurt

1 tsp rice flour to 1 cup yogurt

Also, remove the dish from the heat source & stir yogurt mixture in, then return dish to heat source to warm dish through and you won't get lumps.

This also works with other dairy products to prevent splitting like heavy cream & buttermilk.

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I've also seen another suggestion: strain out the vegetables/meat from the sauce, add yoghurt to the sauce one tablespoon at a time, whisk it in very quickly, and bring the dish back up to a boil, stirring the whole time, before adding a second tablespoon.

I've found that approach to work quite well.

I think the reason this works is that the yoghurt is quickly dissolved in the sauce to the point that there are no macroscopic clumps, and then each microscopic clump of yogurt is deliberately curdled by bringing the sauce to a boil, which prevents macroscopic curdles from forming later, and results in a smooth texture despite thoroughly cooking the yoghurt.

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Surely adding sauce to yogurt a little at a time (essentially tempering, as Bruce Alderson mentioned) is much easier than adding yogurt to sauce a bit at a time; it's hard to catch every clump of yogurt in a lot of liquid with your whisk. –  Jefromi Nov 28 '12 at 22:18
    
@Jefromi In the korma recipe I was following, there isn't that much liquid, at most three cups, and it's quite easy to mix the yoghurt in thoroughly in a 12-inch frying pan. I don't really think "tempering" by adding sauce to the yoghurt would quite achieve the same thing, since you certainly don't bring the yoghurt up to boiling and curdle it while adding the sauce...though that technique would make it easier to mix the yoghurt with the sauce quickly, so it might help in achieving this result without having to add the yoghurt a bit at a time. –  Theodore Murdock Nov 29 '12 at 3:41
    
@Jefromi I think the main difference between this technique and Bruce's notes is that Bruce doesn't advocate cooking the yoghurt at high temperature after it's added. –  Theodore Murdock Nov 29 '12 at 3:42

One option is to substitute cream for yoghurt.

That's what's done in a lot of Indian cooking. When yoghurt is used, it's usually added at the end, and not at high heat, just as James points out.

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Y know, that is more than true - a lot of Moghlai dishes are made with cream, and a lot of recipes substitute yoghurt for the cream because it is a healthier option. A side effect is that yoghurt makes the dish less rich, so you can face eating more of it! I could never get more than halfway through a dish of truly creamy Pasanda, but I finish the plate if yoghurt is used. –  James Barrie May 16 '11 at 20:37

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.

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In addition to reducing the temperature of the curry, you can also:

  • Temper the yoghurt - combine a small amount of the warm sauce to the yoghurt before adding it to the curry. This helps when adding cream, milk, or eggs to a sauce.
  • Whisk the yoghurt - use a fork or whisk and vigorously mix the yoghurt. As the fats and proteins are emulsified in the liquid, this ensures an even starting distribution.
  • Add an emulsifier - add a teaspoon of mustard powder or lethicin to the curry before combining the yoghurt.
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