Semolina

Semolina is durum endosperm in granular form. Durum milling proceeds through a long sequence of break rolls, sifters, and purifiers — the purifier being the machine that distinguishes this milling system, using air currents over a sieve to separate light bran-bearing particles from denser pure endosperm of the same size. The mill is judged on how much clean semolina it recovers at the target size with the fewest bran specks.

Purification

Air-and-sieve separation of particles by density as well as size, removing bran-attached fragments that a sifter alone would pass.

Specks

Visible dark particles of bran or black-point-affected material carried into the semolina. Counted, because they show in the finished pasta.

Ash content

A mineral measure used as an indirect indicator of how much bran material a semolina contains.

Particle size and its uniformity govern hydration and therefore dough behaviour. Protein content and quality govern the firmness of the cooked pasta and its resistance to overcooking. Colour — the bright amber-yellow the market expects — comes from carotenoid pigment carried in the grain and is diminished by oxidative enzymes during processing, so it depends on both the durum bought and how it was handled. Speck count and ash together describe how cleanly the mill separated bran.

Names vary and are not interchangeable across markets. Coarser and finer semolina grades, and the finer durum flour beyond them, are defined within particular national compositional standards, and pasta laws in several jurisdictions specify what may be used to make a product sold under a given name.

Semolina is stored and shipped in bulk and in bags. It is hygroscopic, and because its particles are large and free-flowing, it segregates by size during pneumatic conveying and in silos — a coarse fraction and a fine fraction can separate in transit, which matters when the buyer specified a distribution. It supports storage insects like any milled cereal product, so stock rotation and hygiene in bins and pasta plants are routine practice.