Ask Peter splitting yoghurt

I like to make curries that include yoghurt but invariably they end up boiling and the sauce curdles. I could add the yoghurt at the end but I want the flavours to meld. Some people swear by only stirring the curry in one direction when the yoghurt is added. Really? My curries taste good but they are not great lookers. Please help — I’d like to serve them to guests! Justine

I’ve spoken to a few friends who make a mean curry and it seems that the higher the fat content in the yoghurt the less likely it is that it will curdle when heated. Low-fat yoghurt will split if heated too much, so as long as you don’t bring the curry to the boil it’ll likely stay together, as it were. I’ve read that originally the yoghurt used in curries was made from buffalo milk, as these were the working animals used to plough fields in certain areas of India so it was simply what was around. You’ll know, if you’ve ever eaten buffalo milk burrata or buffalo mozzarella, that the milk is incredibly rich and fatty — but not fatty like butter or cow’s cream. It has a certain richness, and lower protein than cow’s milk, that is both appealing and also vaguely healthy — but this might be me being delusional. Anyway, buffalo yoghurt apparently doesn’t curdle as easily when heated. I’ve yet to test that myself (it’s not as though buffalo yoghurt is super-easy to source) but it makes sense. I’ve also read several Indian cooking websites that do say that stirring in the yoghurt in one direction only is also a way to avoid curdling. This does sound bonkers I know, but it appears again and again so there must be some truth to it. I think it has something to do with not breaking up the straight structure of the lactic proteins, so not making them go higgledy piggledy … I’m no scientist but I sort of get it. Just.

Other pointers are that you should only add yoghurt that’s at room temperature — not straight from the fridge. The act of adding cold yoghurt to a hot liquid will likely cause it to be shocked into splitting. The same happens when adding (most) cold soy milks to a hot espresso — the difference in heat causes problems — and as someone who drinks soy flat whites I can attest to the fact there’s nothing more revolting than a split soy coffee. So, you’ll need to temper your yoghurt — take 1 cup of room temperature yoghurt and gently stir in ¼ cup of the hot liquid from the curry. Once it’s emulsified, stir in another ¼ cup and repeat until you have 1 cup of each. Turn the heat of the curry down to a gentle simmer then gently mix the tempered yoghurt back into the curry and cook over a very low heat for a few minutes and no more — unless it looks like the curry isn’t going to split.

Also, you can help stabilise the yoghurt by whisking 1 cup room temperature yoghurt with 1 ½ teaspoons of various flours: cornflour (which won’t affect the flavour), potato flour, chickpea flour (besan — which would seem more authentic but it does have a slight flavour) or even wheat flour. Sieve the flour over a few tablespoons yoghurt and gently whisk in one direction to make sure you have no lumps, then gently whisk in (in one direction) the remaining yoghurt. Temper as above — adding hot liquid to the floury yoghurt. The flour will also slightly thicken the curry, but not enough to be a worry.

I know you’d like to make your flavours meld, but is this really necessary? If you wanted a more creamy curry you could use coconut milk (as in many Thai curries) or creme fraiche. If it’s the tanginess of yoghurt you’d like to work with, you could stir a little extra tamarind paste, pomegranate molasses or lime juice in at the end — but go easy, as acidity will curdle dairy proteins. Most of all, just don’t boil the curry once you’ve added the yoghurt or you’re asking for trouble!