Fresh Herbs: Hardy, Delicate, and When to Add Them

Aroma is volatile, so timing is the whole game

Herb aroma comes from compounds with low boiling points — well below the temperature of boiling water, so they are leaving for the air long before the pan gets hot. Which means when you add an herb changes the dish more than how much you add.

The same handful of coriander stirred in at the start becomes a quiet background in the broth; scattered over the bowl at the end it is the loudest thing in the dish. That is not a difference of quantity. They are different dishes.

Hardy and delicate herbs are different ingredients

This distinction is the most useful thing on this page.

• Hardy herbs — rosemary, thyme, oregano, sage, bay. Thick leaves, aroma held inside a waxy layer, so they survive heat. They go in early, or their flavour never comes out and you are left chewing a tough leaf.
• Delicate herbs — coriander, basil, parsley, dill, mint, perilla, spring onion greens. Thin, wet leaves that collapse on contact with heat. They go in off the heat, or in the last thirty seconds.

That is why thyme and bay go into bouillabaisse and Irish stew from the beginning, while the coriander in pho and banh mi only meets the dish in the bowl. Same for the dill in lohikeitto and borscht.

The stems carry more aroma than the leaves

Coriander stems are more concentrated than the leaves and far more heat-tolerant. They are not trimmings.

Stems early, leaves at the end makes one bunch of herbs work on two levels, which is exactly how Thai and Vietnamese cooking uses it. Parsley stems belong in stock. Basil stems are the exception worth discarding — they taste coarse.

Basil never meets a knife

Finely chopped basil oxidises where the blade cut it: it turns black and leaves its aroma on the board. Tear it by hand, or stack the leaves, roll them, and make one clean cut. You can see the difference plainly in caprese and pesto pasta.

Parsley and coriander suffer a milder version of the same thing — chop them too fine and the juice ends up on the board. Drying the leaves completely before chopping helps more than a sharper knife.

The exception: herbs that need frying

Every rule has one, and this exception defines a dish.

Thai holy basil needs to be fried in oil for its aroma to appear at all. Scatter it over pad kra pao at the end and you have made something else. It shares a name with Italian basil and little else.

Dried hardy herbs behave the same way — they release into fat, not water (blooming spices).

Storage — treat delicate herbs like flowers

• Delicate: trim the stem ends, stand them in a glass of water, bag them loosely, refrigerate. Keep the leaves out of the water or they rot. Coriander and parsley will hold a week or more.
• Hardy: wrapped in a damp paper towel, in a sealed box, in the fridge.
• Freezing: chop, pack into an ice cube tray, top with olive oil, freeze. Leaves frozen bare turn to water when they thaw; frozen in oil they go straight into the pan (freezing and thawing).

Substitutions only work among the hardy herbs

Dried can stand in for fresh only for hardy herbs. Use about a third as much (1 tbsp fresh ≈ 1 tsp dried) and add it early.

Dried delicate herbs are not substitutes, they are different ingredients — dried coriander leaf and dried parsley have almost no aroma left. And swapping parsley for coriander is not a substitution either. Coriander's character comes from aldehydes that parsley does not contain, and in som tam or ceviche that character is the dish. Better to make it without and add freshness from another direction — lime, or spring onion (balancing flavour).

Korean perilla works the same way. The perilla in golbaengi-muchim and jeyuk-bokkeum does not become lettuce.