1. We should be careful that the oil is not too hot when frying onions. Stir-fry time should not be too long, but stir-fry frequently.

2. Sauce and vinegar are not needed for frying onions. The paint is soy sauce, which can be called "stain" for kitchen dishes. In addition, you can't add salt when frying onions. Adding salt will make onions overflow with water, and the osmotic pressure is unbalanced, so it looks very black when frying.

3. Onion is a quick-cooked vegetable. Generally, it can keep its original color well when it is quickly fried, blanched and cooled, and then fried thoroughly. Do not cover the pan when frying onions, because the organic acid in onions is difficult to volatilize, forming an acidic environment that makes onions turn black.