Over-fried curry leaves in tadka will turn dark brown or black, become brittle, and emit a burnt, bitter smell instead of their characteristic fragrant aroma. The oil may also darken and take on a burnt flavor.
Curry leaves are a delicate ingredient, and their flavor can easily be ruined if overcooked. Here's a breakdown of the signs to watch out for:
Color Change: Fresh curry leaves are a vibrant green. As they fry, they will darken slightly. However, if they turn a deep brown or black, they are over-fried.
Texture: Properly fried curry leaves should be slightly crisp but still pliable. Over-fried leaves become extremely brittle and crumble easily.
Smell: Fresh curry leaves have a distinct, fragrant aroma that is released when they are fried. Over-fried leaves will lose this aroma and instead emit a burnt, bitter smell.
Taste: Over-fried curry leaves will impart a bitter, unpleasant taste to the tadka and the dish it's flavoring.
Oil Appearance: The oil used for the tadka may also darken significantly if the curry leaves are over-fried, indicating that they have released burnt compounds into the oil.
Add curry leaves towards the end of the tadka process, after the other spices have bloomed, and fry them for only a few seconds until they become slightly crisp and fragrant. This prevents them from burning and ensures their flavor is preserved.