What Is the Difference Between Herbs and Spices?

Herbs are the leaves of a plant, usually soft and green, used fresh or dried. Basil, parsley, coriander leaf, thyme, mint and rosemary are all herbs.

Spices come from any other part. Cinnamon is bark, ginger is a rhizome, cloves are flower buds, black pepper is a dried fruit, and cumin and coriander seed are seeds. Some plants give both, which is why coriander leaf is a herb and coriander seed is a spice.

Spices generally hold their flavour compounds in tougher, drier tissue, so they need heat and time to release them. Herbs hold volatile oils in delicate leaves that are destroyed by prolonged cooking.

That leads to a practical rule:

• •Add whole or ground spices early, often bloomed in hot oil first
• •Add hardy herbs like rosemary and bay early, since they tolerate long cooking
• •Add soft herbs like basil, coriander and parsley at the very end
• •Toast whole spices briefly before grinding to deepen their aroma

Herbs grow almost anywhere and are best used fresh, so they were never worth transporting far. Spices dry well, keep for years and grew only in specific tropical regions, which made them ideal trade goods and enormously valuable.

That combination drove centuries of trade routes, exploration and conflict. Nutmeg and cloves came originally from a small group of Indonesian islands, and control of that supply was fought over by European powers repeatedly. The search for a sea route to the spice producing regions is what sent European ships around Africa and across the Atlantic.

Drying concentrates some flavours and destroys others. Hardy herbs such as oregano and thyme dry well because their aromatic compounds are relatively stable. Soft herbs such as basil and parsley lose most of their character and are best used fresh.

Spices are almost always used dried, and whole spices keep far longer than ground ones. Grinding exposes an enormous surface area to air, so ground spices lose potency within months while whole ones stay usable for a year or more.

Both lose potency through exposure to heat, light, air and moisture, which is why the rack above the cooker is the worst possible place to store them.

A few practical rules help considerably:

• •Store in sealed containers in a cool dark cupboard away from the hob
• •Buy whole spices where possible and grind small amounts as needed
• •Replace ground spices roughly annually, whole spices every few years
• •Dry hardy herbs yourself, but buy soft herbs fresh rather than dried
• •Toast whole spices in a dry pan for under a minute to revive older stock

Some spices come from surprising plant parts. Saffron is the dried stigmas of a crocus flower, with only three in each bloom, and they are picked by hand, which is why saffron is so costly. Vanilla is the cured seed pod of an orchid. Outside its native region in Mexico, the flowers usually have to be pollinated by hand, because the insects that pollinate them naturally are absent. Allspice, despite its name, is not a blend. It is the dried berry of a single tree, named for a flavour that reminded Europeans of several spices together.

The advice to bloom spices in hot oil has a chemical reason. Many of the aromatic compounds in spices dissolve much better in fat than in water. Warm oil draws them out of the dried tissue and then spreads them evenly through a dish, which is why curries often begin by frying spices before liquid is added. Fat carries flavour in herbs too. A basil or parsley oil captures their fragrance, and finishing a dish with a little olive oil can help soft herb flavours reach your nose.

The burn of chilli is not a taste at all. Capsaicin, the main hot compound in chillies, binds to a receptor on nerve endings called TRPV1, which normally responds to temperatures above about 43 degrees Celsius. Your brain receives what is essentially a heat alarm, which is why chilli can make you sweat and flush. Piperine, from black pepper, acts on the same receptor more gently. Chillies come from the Americas and were called peppers by Spanish explorers because their heat reminded them of the black pepper they had been seeking.

Mustard, horseradish and wasabi produce a different kind of heat that rushes up the nose and fades quickly. The plants store harmless compounds and an enzyme in separate parts of their cells. Grating, chewing or mixing with water brings them together and releases allyl isothiocyanate, a volatile chemical that triggers a related receptor called TRPA1. Because the reaction begins only when tissue is damaged, wasabi is at its sharpest just after grating, and mustard powder needs to stand in cold water for a few minutes before it develops full strength.

The kitchen meaning of herb is not the same as the botanical one. To a botanist, a herb is a herbaceous plant, one with soft, non-woody stems that die back after flowering or at the end of the growing season. By that standard rosemary and thyme, which grow as small woody shrubs, are not herbs at all, and bay leaves come from a tree. Cooks use the word for the leaves regardless, so the culinary meaning describes how a plant part is used rather than what kind of plant produced it.

Several plants sit on both sides of the line. Dill gives feathery leaves used as a herb and seeds used as a spice, and fennel does the same. Names can mislead too. Curry leaves come from the curry tree, a relative of citrus, and are used fresh in South Indian cooking, while curry powder is a blend of spices such as turmeric, coriander seed and cumin that has nothing to do with that tree. Garlic, onions and shallots are usually treated as neither herbs nor spices, and are often grouped as aromatics, because cooks use them in large quantities as a flavour base.

A popular story claims that medieval Europeans used heavy spicing to disguise meat that had gone off. Historians of food have found little support for it. Spices such as pepper, cloves and nutmeg were imported over enormous distances and were expensive, so the households that could afford them could also afford fresh meat. Towns regulated butchers closely, and records show sellers being punished for selling spoiled food. Spices did not make rotten meat safe either, and nobody with a choice would pay a fortune to make bad food only slightly less unpleasant.

The real reasons were status, flavour and health. Spices were a visible sign of wealth, and surviving recipes show cooks using them generously in sweet and sour combinations, with ginger, cinnamon, saffron and pepper appearing together in the same sauce. Medical theory of the time, inherited from ancient Greek writers, classed spices as warm and dry and held that they aided digestion and balanced the body. Some spices do contain compounds that slow the growth of microbes, but salting, drying and smoking did the real work of preserving meat. The spice trade was driven by desire rather than necessity.

Herbs are the leaves and spices are every other part of the plant, and because spices store their flavour in tougher tissue they need heat and early addition while soft herbs should go in at the end.