Well it depends in fact, it depends on the herb itself or more exactly its active principle, its essential oil if you prefer, and which must pass from the herb in the dish for our greatest happiness.
And there attention, all the herbs are not equal, because the active ingredient they contain supports more or less well the heat.
Here is a specific example, tarragon, its active ingredient is estragol and unfortunately estragol evaporates at 50°C (approximately) which means that if you put it in a dish that goes in the oven for a long time, well it's almost useless because the taste will have evaporated during cooking and in the best case there will just be traces of it. Disappointing...
What to do?
All is not lost, it is enough to proceed differently, and to add the chosen herb at the last moment, the dish already taken out of the oven, and a few minutes before serving. This way you will have the expected taste, and in addition a certain freshness of taste due to the fresh herbs added. This is especially true for herbs that are very sensitive to heat: chives, tarragon and chervil in particular.It is a little less true for parsley which is less sensitive to heat, and can be cooked better.
Another way to do it is to combine the 2 methods: herbs at the beginning for more nuanced notes, and herbs at the end for fresher and more pronounced notes.
Does this apply to all herbs?
No, there are some that have an active principle with a very high evaporation temperature (like 250°C), but with those you can go ahead and let it simmer or infuse for a long time: bay leaf, thyme and vanilla for example.To sum up: For a recipe with herbs, and depending on the herbs, it is often better to incorporate the herbs at the end of cooking, chopped up at the minute.
