Mustard seed

• raiराई

  Hindi

  Rai is the small brown or black seed used across South Asia. Sarson usually means the larger yellow seed and the plant grown for its greens and oil.

• mostaza

  Spanish

• khardal

  Arabic

• moutarde

  French

Depends entirely on treatment. Wetted and left cool, it is sharply pungent — sinus heat rather than tongue heat. Heated in fat without water, the pungency never develops at all and the seed turns nutty and mild. The same seed produces two opposite results, and knowing which you want is the whole skill.

Almost nothing when whole and dry. The characteristic smell appears only after the seed is crushed and wetted, when an enzyme reaction generates the pungent compounds — this is the most distinctive thing about the spice and is unlike anything else in the cabinet.

Yellow seed is pale straw and noticeably larger; brown and black seeds are smaller and range from red-brown to near black.

Hard round seeds that pop audibly in hot fat. They stay whole in a finished dish and are pleasant to bite, which is why South Asian tempering leaves them visible.

• Allyl isothiocyanate — From sinigrin in brown and black seed. Volatile and sharply pungent — the compound behind the nasal hit, and the reason that heat fades within minutes.
• p-Hydroxybenzyl isothiocyanate — From sinalbin in yellow seed. Non-volatile, so it produces a milder heat that stays on the tongue rather than rising into the nose.
• Myrosinase — The enzyme that makes the whole thing work. Water activates it; heat destroys it, which is why the order of operations decides the result.

Decide which mustard you want before you start, because the two are mutually exclusive. For nutty and mild: drop whole seeds into hot fat, cover — they jump — and wait for the popping to slow. For pungent: crush or grind, add cool water, and wait ten minutes; add acid only after the heat has developed, since acid arrests the reaction and locks in whatever you have. Never use hot water for the second, and never expect heat from the first.

Two techniques and two opposite results. Popped whole in hot fat, mustard seed is nutty, mild and textural — the opening move of an enormous range of South Asian dishes, and the reason tempered dal tastes the way it does. Crushed into a cool liquid, it is fiercely pungent and becomes mustard, vinaigrette and sauce. It is also standard in pickling liquors and in cured meats across northern Europe. It works with potatoes, cabbage and root vegetables, with pork and beef, with cheese, with lentils and with oily fish, and its sinus heat cuts fat in a way chilli does not.

• grinding — Grinding alone does little while the seed is dry. Grinding and then adding cool water starts the reaction; the pungency peaks after several minutes and then declines as the volatile compounds escape.
• frying — Whole seeds dropped into hot fat pop and turn nutty. The heat destroys myrosinase before any water is present, so the pungency never forms — this is why tempered mustard seed in a South Asian dish is mild and nutty rather than hot.
• boiling — Hot liquid added to ground mustard denatures the enzyme before it can act, giving a mild, bitter result. Anyone who has made mustard with boiling water has discovered this the hard way.
• toasting — Dry-toasting develops nuttiness and forecloses the pungency entirely, for the same reason as frying.

Test the reaction rather than the smell, because dry mustard smells of very little whatever its age. Crush a few seeds, or mix a little powder with cool water, wait ten minutes and taste. Fresh mustard bites; spent mustard is merely bitter.

• No heat developing ten minutes after wetting
• Bitterness with no sharpness behind it
• Caking or clumping in powder
• Any sign of insect damage in whole seed

• Moisture uptake, which triggers and then wastes the pungency reaction in the jar
• Oxidation of the seed oils
• Caking in the powder
• Insect damage in whole seed held long and warm

Buy whole seed, and buy powder as well if you make dressings or English mustard. They are not substitutes for one another. Whole seed keeps for years because its pungency has not been made yet — the precursors are stable in a way finished aroma compounds never are — while powder degrades in a specific, diagnosable way: it stops making heat. Grinding whole seed at home is easy, so the case for buying powder is convenience and the case for buying seed is that it will still work in three years.

• A stated species or colour — yellow, brown or black — since pungency differs substantially between them.
• Plump, uniform, dry seed with little dust or pod material.
• Whole seed rather than powder, unless powder is specifically wanted.
• For powder, a recent date, since its ability to generate heat is what fades.

Graded on species, seed size, colour and admixture. The practically useful distinction for a cook is the species rather than the grade: yellow seed is mild and is what makes American-style mustard, brown is hotter and is the South Asian tempering seed, and what is sold as black is usually brown.

Brassicaceae

Fast-growing annuals with yellow flowers and slender seed pods. Brassica nigra grows tall and drops its seed readily when ripe, which is precisely why it lost commercial ground to the more tractable Brassica juncea once harvesting mechanised.

Sinapis alba in the Mediterranean and Near East; the Brassica mustards in a broader Eurasian range with a long history of cultivation across South Asia and China.

• Nepal — major producer. Among the largest producers of mustard seed, much of it pressed for oil.
• Russia — major producer
• Canada — major producer. The dominant exporter of yellow and brown seed to the condiment industry.
• India — major producer
• France (Burgundy) — historic producer. Historically central to Dijon mustard, though much of the seed used there is now imported.

Cut or combined when the pods have turned and before they shatter. Shattering losses are the reason Brassica nigra is now uncommon commercially despite being the traditional black mustard.

1. Harvesting and threshing — Pods are cut or combined and threshed to release the seed.
2. Cleaning and grading — Cleaned of pod material and graded by size, colour and species purity.Why: Species purity matters because yellow and brown seed have materially different pungency.
3. Drying — Dried to a low moisture content for storage.Why: Critical here beyond the usual reasons: the pungency reaction needs water, so a damp seed has already begun losing its potential.

Graded on species, size, colour and admixture. The condiment industry buys to tight specifications because the yellow-to-brown ratio determines the heat of the finished mustard.

Whole seed is cheap and hard to falsify. Species substitution — brown sold as black, or a cheaper species blended in — is the realistic issue, and it changes the pungency of the result.

Direct-sown as an annual and grown to maturity over roughly three to four months. Also grown as a green manure and cover crop, which is a use unrelated to the spice trade.

Cool temperate. Mustard is a short-season crop that suits climates too cool for most spices, which is why it is one of the very few spices grown at scale in Canada and northern Europe.

Mustard is one of the oldest condiment plants of Europe and Asia, documented in classical Mediterranean sources and long established in South Asian and Chinese cooking. Unlike the tropical spices it grew readily in temperate Europe, which made it cheap and universal at a time when pepper was neither.

Never a monopoly commodity — mustard grows in cool climates and was available locally across Europe throughout the period when tropical spices were luxuries. Modern trade is dominated by the condiment industry, with Canada the principal exporter of seed.

Mustard plasters and poultices have a long documented history in European folk medicine, exploiting the same isothiocyanates that make the seed pungent. Recorded as documented tradition, not as a health recommendation, and the counter-irritant effect is a reason for care rather than for use.

• Mustard is a declared allergen requiring labelling in the European Union and the United Kingdom.