Ingredient

Mustard seed

Mustard is a chemistry lesson disguised as a condiment. The seed itself is not hot. Its pungency is created the instant the seed is crushed and wetted, by an enzyme reaction — and what happens next depends entirely on temperature, which is why frying mustard seeds makes them nutty and mixing them with cold water makes them fierce.

The reaction, and why temperature decides everything

A mustard seed stores glucosinolates in one compartment and an enzyme called myrosinase in another. Nothing happens while they are apart. Crush the seed and add liquid and they meet, and the enzyme converts the glucosinolates into the pungent compounds that make mustard hot.

That reaction needs water and it needs the enzyme to be intact. Heat destroys the enzyme.

Hence the two opposite behaviours. Fried whole in hot oil, as in an Indian tadka, the seeds pop, the enzyme is destroyed before it can do much, and what you get is a nutty, faintly bitter, aromatic flavour with almost no heat at all. Ground and mixed with cold water, the enzyme works freely and the result is savagely pungent within minutes.

It also explains why English mustard powder is mixed with cold water and left to stand for ten minutes before serving — that is the reaction happening — and why mixing it with hot water or vinegar straight away gives a much milder mustard. Vinegar stops the reaction where it is, which is how a mustard's heat is set at the intended level and preserved.

The seeds

Yellow / white mustard

The mildest. Pungency is broad and nasal rather than sharp, and it fades quickly. The base of American mustard and of most mild European mustards.

Brown mustard

Sharper and hotter. Used in Dijon, in many European mustards, and widely in Indian cooking.

Black mustard

The hottest and most pungent. Traditional in Indian cooking, particularly South Indian, where the seeds are fried whole.

Mustard powder

Ground seed, usually a blend, sometimes with turmeric and flour. English mustard powder is largely brown and yellow seed and is very hot when freshly mixed.

Wholegrain mustard

Seeds left partly whole in a vinegar and wine base. Texture as much as heat.

Dijon

Brown seed with wine or verjuice rather than vinegar. Sharp, smooth, and the standard for dressings and sauces.

How to use whole seeds

• Tadka or tempering. Hot oil, mustard seeds added until they pop and jump, then curry leaves, chilli and other spices, then the lot poured over a dal or a vegetable dish. The single most important use in Indian cooking.
• Wait for the pop. Seeds added to oil that is not hot enough will not pop and will taste raw and bitter. Seeds left too long burn and go acrid. The window is short and audible.
• Use a lid. They genuinely jump out of the pan.
• In pickling liquids, whole, where they soften and give a mild mustard note.
• In chutney and piccalilli.
• Toasted and crushed into a rub or a crust for meat or fish.
• In a cabbage or potato dish, fried in butter, which is a very good European use of an Indian technique.

How to use made mustard

• In a vinaigrette, where it is doing a mechanical job as well as a flavour one: mustard is an emulsifier and helps oil and vinegar stay combined. Dijon is the standard.
• In cheese sauces and macaroni cheese, where a small amount sharpens the dairy without being detectable as mustard.
• On meat before roasting, as a coating that helps a crust adhere.
• In a pan sauce, whisked in off the heat — boiling a mustard sauce hard drives off its pungency.
• Added late. Heat degrades the pungent compounds, which is why a mustard sauce should be finished with mustard rather than simmered with it.
• With cheese, ham, sausages and cold meat, which is what most of it is for.

Common questions