Add fresh herbs like cilantro or mint towards the very end of the cooking process, typically in the last few minutes or even after the heat is turned off, to preserve their delicate flavors and aromas.
Fresh herbs contain volatile oils that are responsible for their distinct flavors and aromas. These oils are easily damaged or evaporated by heat. Adding herbs early in the cooking process exposes them to prolonged heat, causing these oils to dissipate, resulting in a muted or even bitter flavor.
To maximize the impact of fresh herbs:
Chop the herbs: Finely chop the herbs just before adding them to release their flavors.
Add at the end: Stir the chopped herbs into the dish during the last few minutes of cooking, or even after you've turned off the heat. The residual heat will be enough to release their aroma without destroying their flavor.
Consider the herb: Some heartier herbs like rosemary or thyme can withstand longer cooking times, but delicate herbs like cilantro, parsley, mint, and basil are best added at the very end.
If you're adding fresh herbs to a cold dish, such as a salad or salsa, add them just before serving to prevent them from wilting or discoloring.