Mustard Powder vs. Mustard Seed: Heat, Storage and How Much to Swap

Mustard powder is just mustard seed ground fine, and a jar of it doesn’t smell hot at all. Neither form is hot until crushed seed meets water, which lets the enzyme myrosinase turn a compound stored in the seed into sharp, nose-tingling allyl isothiocyanate.¹ The difference is what you can do with each. Powder blends into liquids and dry mixes right away. Whole seed keeps longer, adds texture, and can be fried in oil, which turns it nutty and smoky instead of hot.²

Side by side

ATK’s keeping times are a general rule for whole and ground spices, not something measured for mustard.⁶ For each form on its own, see mustard powder, yellow mustard seeds, brown mustard seeds and black mustard seeds.

The heat is made, not stored

You’ll often read that grinding mustard “releases” its volatile oils, which then drift out of the jar. The chemistry doesn’t work that way. Crushed seed holds an enzyme, myrosinase, and a glucosinolate called sinigrin. Water brings them together, and the reaction forms allyl isothiocyanate, the highly volatile compound behind mustard’s kick.¹ Until that happens, dry powder has no smell. So a jar of mustard powder doesn’t smell hot, and a pinch in a dry rub does very little until it gets wet.

Yellow mustard works a little differently. Its glucosinolate is sinalbin, and what forms is a pungent compound that’s non-volatile.⁴ That’s why yellow mustard bites on the tongue without much of the nasal rush of brown or black.

That doesn’t mean powder keeps forever. ATK says to buy spices whole and grind them just before use, and gives about two years for whole spices against one year for ground.⁶ McCormick says mustard seeds tend to be more potent than ground mustard.⁷ Neither source measured how fast mustard powder loses strength, and we found no study that did.

How each behaves in cooking

Water temperature controls the heat. Popular Science reports that water that’s too hot shuts down myrosinase completely, while cold water works slowly, so mustard mixed with cold water needs time to rest.¹ A lab study on brown mustard seed found the same pattern: the higher the temperature across 30 to 80°C, the more enzyme was inactivated.⁸ That goes for powder and cracked seed alike.

Vinegar locks it in. Strong acid like vinegar completely blocks myrosinase, according to Popular Science.¹ Wet powder or cracked seed with water first, let it develop, then add vinegar to set the heat where you want it.

Frying turns seeds nutty. Frying whole seeds in fat is a typical South Indian technique. Katzer notes that seeds fried in fat or dry-toasted lose their pungency and taste nutty and smoky, and that heating quickly destroys any isothiocyanate already formed.² So tempered seeds add flavor and texture, not heat. Powder can’t do this job. There’s no whole seed to pop, and ground spices tend to scorch in hot fat.⁵

Emulsifying. Mustard seeds contain emulsifiers, Katzer notes, so mustard makes emulsified sauces more stable as well as tastier.⁴ Powder disperses into a vinaigrette or mayonnaise at once; whole seed doesn’t.

Can one stand in for the other?

How much seed equals a teaspoon of powder

The sources disagree, and McCormick’s figure measures something different:

McCormick’s figure is a volume conversion: how much powder you get when you grind a teaspoon of seed. It says nothing about strength. NDSU’s is a kitchen equivalence. McCormick also says seeds tend to be more potent than ground mustard,⁷ which fits NDSU’s smaller amount.

Where to start: 1/2 teaspoon of seed per teaspoon of powder, ground fine and wetted before it goes in. Going the other way, use 1 1/2 to 2 teaspoons of powder per teaspoon of seed. McCormick’s chart gives the lower figure, and NDSU’s equivalence implies the higher one. Taste before adding more.

Which way the swap works

In pickle brine. Whole white mustard seeds are popular in pickled vegetables. Powder will flavor a brine but can cloud it. For blends, see pickling spice and corned beef and cabbage spices.

Which to keep on hand

• Powder if you mostly make dressings, cheese sauces, glazes, rubs and quick mustard pastes. Mix it with cool water first when you want heat.
• Seed if you cook Indian food, pickle, or make your own whole-grain mustard. It keeps longer by ATK’s general rule,⁶ and you can grind it to powder whenever you need to.
• Both, if you do a bit of everything. Seed is the more flexible of the two, since it can become powder but not the other way around.

For more on the seeds, see mustard seed uses; for the powder, mustard powder uses.

What isn’t known

• No study measures how fast mustard powder loses pungency in storage compared with whole seed. The keeping times above are ATK’s general guideline for all spices.
• We found no published weight for a teaspoon of whole mustard seed, so there’s no way to convert between seed and powder by weight.
• Labels rarely say which seed a given powder is made from.

Related

• Mustard powder and mustard powder substitutes
• Yellow mustard seeds, brown mustard seeds and black mustard seeds
• Black mustard seed substitutes
• Mustard powder vs. prepared mustard and yellow vs. black mustard seeds
• Panch phoran and curry leaves, partners for tempered seeds