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:
- 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.
- How long on average do you need to cook the mixture until the oil separates?
- What causes the oil to separate? Is it simply that all the water has been cooked out of the mixture?
- Why do you need to let the oil separate?