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A lot of Indian curry recipes have a step where you're told to cook an onion-tomato-spices mixture "until the oil separates". Despite having tried cooking such recipes a number of times already, I still haven't really figured out what is meant by this. I have several questions:

  1. How can I tell that the oil is separating? I'm never quite sure whether I'm seeing oil or water coming out of the mixture while it's cooking.
  2. How long on average do you need to cook the mixture until the oil separates?
  3. What causes the oil to separate? Is it simply that all the water has been cooked out of the mixture?
  4. Why do you need to let the oil separate?
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up vote 14 down vote accepted

1 - Oil is separated in curries normally after you have cooked spices or sauces for ~10-15 mins. You can tell by seeing "bubbles" appearing and the oil by making a thin layer on top of your sauces/curry.

2 - It varies, but normally after 10-15 mins the oil separates from your curry.

3 - Normally after cooking for 10-15 mins most of the water dries up which causes the curry (mostly made of thick sauces) to separate from the oil.

4 - It's always good to let the oil separate from your curry because of two things:

a - Extra water dries up
b - All spices and curry get cooked properly

The food tastes much better if spices and the curries are properly cooked.
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Pretty good Nadia. I wouldn't put a time on the cooking as this depends on individual conditions, like wetness and temperature. Do you cook at high temp. or low temp.? – BaffledCook Dec 30 '10 at 16:37
Why does the oil separating indicate that "the spices and the curry get cooked properly"? I would like to understand if the answer is simply that the extra water dries up, or is there really any other reason which can be scientifically justified for the "wait until oil oozes out" rule. – dan12345 Feb 4 '14 at 17:08
@dan12345 there are some things in life that help as indicators. The oil separating in and of itself isn't an improvement, it just lets you know that it's ready. Kinda like when making fudge, you know it's starting to be ready when the top goes satin, or your gravy is ready because the roux in the gravy has started to kick. Or cookies are almost ready because you can smell them. It's not alway temp alone, but time spent at a temp. – Escoce Apr 1 at 15:24

Nadia is right. Use your nose and ears too. After a while the sauce will lose its watery appearance and the rawer flavours in the air emanating from the pan will begin to be repalced with more moorish aromas and a greater sizzling. By these stages you'll see angry looking bubbles of oil around the suace and need to keep stirring. I tend to stir a little longer to prevent sticking while getting my (meat/stock/lentils - whichever- etc) ready to pour in.

I find the stage is easy to identify by colour in the case of Tomatoey sauces. these tend to develop a browner appearance by the oil-separating stage.

Oniony-garlicky-gingery mush sauces lose their raw aroma and then their wateriness and start to develop the oil bubbles after a while - about 10-15 as Nadia says. Some great meat curries add the meat and dry spices to the still cooking onion and it gets a refry from the maet juices until drying again. When its really sizzling and sticking to the pan in goes the water, stir until boiling, and on goes the lid for slow cooking

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