Mustard gets its sharp heat from a reaction between enzymes and compounds inside the crushed seeds.

The longer version

Whole mustard seeds are nearly odorless until they are crushed and mixed with liquid. Breaking the cells lets an enzyme called myrosinase reach sulfur-containing compounds stored elsewhere in the seed, and the resulting reaction produces sharp, volatile isothiocyanates.

That pungency hits the nose rather than the tongue, which is why prepared mustard can feel hot in the sinuses. Heat and acid both affect the enzyme: warm liquid destroys the sharpness more quickly, while acidic liquid preserves it longer. Different seed colors and different liquids give the condiment a wide range of intensities, from a mild table spread to a sharp paste that clears the sinuses.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.