Semolina
Coarsely milled durum wheat. The particle size is the point, and it is why semolina cannot simply be swapped for flour.
Also called durum wheat semolina (INTERNATIONAL); semola (INTERNATIONAL); rava (INTERNATIONAL); sooji (INTERNATIONAL); fine semolina (INTERNATIONAL)
Semolina is durum wheat milled coarsely rather than to a fine flour. Two things follow from that, and both matter more than the fact that it is a different species.
THE PARTICLE SIZE CHANGES HOW IT TAKES UP WATER. Coarse particles hydrate more slowly and less completely than fine flour, so a semolina dough often needs resting time simply to finish absorbing what it was given, and a batter made with it thickens for some while after mixing. Finely milled durum — sold as durum flour or semola rimacinata — behaves much more like ordinary flour, and the two are frequently sold under overlapping names.
DURUM IS A HARD WHEAT with strong, relatively inextensible gluten. That combination suits extruded pasta, where the dough must hold a shape and resist rather than stretch, and it is why durum is the pasta wheat. In bread it contributes chew and colour and is usually blended rather than used alone.
Its other common use in baking is as a dusting rather than an ingredient: coarse semolina on a peel or a tray acts as tiny rollers and stops dough sticking without being absorbed into it the way flour is.
What changes if it is left out
Where it was dusting a surface, coarse polenta or rice flour do the same job. Where it was structural — in a durum bread or a semolina cake — ordinary wheat flour changes the texture, the colour and the water uptake at once, and is not a like-for-like swap.
Follows from the particle size and species differences recorded above.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
The science behind it
The clearest case in the catalogue that particle size is a flour variable in its own right: coarse durum and finely milled durum are the same wheat behaving differently.
Can stand in for
Wheat flour— only where the coarser particle and slower hydration are wanted
Not a like-for-like swap. Coarse particles hydrate more slowly and less completely, so a dough can be stiff at mixing and slack twenty minutes later — and the colour and chew change with it. Finely milled durum is much closer, and the two are sold under overlapping names.
Covered in
Substituting one flour for another, honestly
Where particle size rather than protein is what makes the swap fail.