Mustard
Also known as Sinapis alba, Brassica juncea, Brassica nigra, mustard seed, Senf, moutarde, senape, mostaza, gorczyca
A seed whose heat does not exist until it meets water, and which works in charcuterie as a binder and emulsifier as much as a flavouring.
Mustard is unusual among spices in that the dry seed is almost inert. The pungency is created, not stored: the seed holds glucosinolates and, separately, the enzyme myrosinase, and only when the seed is broken and wetted do the two meet and generate the isothiocyanates that carry the heat. Dry mustard powder in a jar has no bite until it is mixed with liquid, and the reaction takes some minutes to develop. Hot liquid or vinegar added immediately will denature the enzyme and lock in a mild result, which is why English mustard is mixed with cold water and left to stand while a vinegar-based Dijon stays comparatively gentle.
The species matter. White or yellow mustard, Sinapis alba, is mild and its heat sits on the tongue. Brown and black mustard, Brassica juncea and Brassica nigra, are sharper and their volatiles go up the nose. Most sausage work uses yellow, whole or ground, and the brown seeds appear in the coarser continental and Indian preparations.
In charcuterie mustard does two jobs. The obvious one is flavour, and it belongs to the German, Austrian, Polish and British traditions: bratwurst, bockwurst, the cooked and liver sausages, English sausages, and the brawns and pressed meats where its sharpness cuts fat. The less obvious one is technical. Mustard flour is a genuine emulsifier and a modest binder, thanks to the mucilage in the seed coat and its protein content, and it has been used industrially for exactly that purpose in fine emulsions. A little mustard flour in a bratwurst is doing structural work as well as tasting of mustard.
Whole seed and ground behave quite differently in the finished product. Whole yellow seeds stay largely intact and give a soft pop and a mild burst rather than distributing heat, which is the traditional effect in a coarse sausage or a pickled product. Ground mustard distributes and develops fully in the moisture of the farce, so the same weight is far more assertive. Prepared mustard, the condiment, brings vinegar, salt and water with it and is a different ingredient again.
Mustard is a declarable allergen in the European Union and the United Kingdom, and that is the most important practical note for anyone recording a formula or selling a product. Doses run from about 0.5 to 3 g per kilo of meat for the ground seed, more where whole seed is used for texture.