Wheat and its different grinding techniques
Cereals, thanks to their versatility, high digestibility and their relatively neutral taste, are a basic food product in the Mediterranean Diet (they are at the base of the Mediterranean Diet food pyramid, together with fruits and vegetables).
The grain of wheat is made up of three main parts:
Outer layer (bran). Composed of various layers (integument, pericarp and aleurone layer), it protects the grain and constitutes 14% of it. It mostly contains fibre, but also B vitamins, minerals and phenolic compounds.
Endosperm. This is the middle part and provides nourishment for the germ and constitutes 83% of the grain. It is made up of starch (i.e. complex carbohydrate), protein and small amounts of vitamin B. Starch and protein form gluten.
Inner Germ. Through germination it gives rise to a new plant. It is rich in polyunsaturated fat, vitamins B and E, minerals, phenolic compounds and antioxidants, and it constitutes the remaining 3% of the grain.
As a result of the grinding processes, wheat derivatives inevitably lose their vitamin complex.
In the past, flour production was made exclusively through grindstone but this procedure is now outdated and is only kept in artisanal production. At present, a method called cylinder grinding (or high grinding) is used, where the caryopsis breakage occurs in many steps, during which the single parts separate from each other. In this way, various types of flour are obtained, with different starch, protein, cellulose content and a whole series of bran derivatives.
The product resulting from this grinding method always shows a white colour (in the case of soft wheat flour and a yellow colour (in the case of durum wheat semolina). In order to obtain whole wheat flour or semolina, you have to add a certain percentage of bran to the refined end product, a product that is ‘rejected’ during the decortication phase.
Indeed, the first operation is called decortication and consists of removing the germ and much of the outer bran layer from the grain of wheat.
The second step is grinding: the decorticated wheat goes into the first machine where it is broken by two pairs of metal cylinders rotating in opposite directions; these cylinders have transverse scuffing which break the grain. Milled wheat falls onto an oscillating sieve that holds bigger fragments (residual bran) and lets the smaller ones pass through. This operation is called sifting. This procedure is then repeated in other machines, where cylinders are closer to each other and sieves are thicker. Finally, the product of the previous procedures undergoes a new grinding in machines which have very close, smooth cylindrical rolls.
The sieving rate of flour indicates the quantity of product (in Kgs) obtained from grinding 100 Kg of wheat. The higher the grade, the coarser the flour. “00” flour has undergone a sieving of 50%; “0” flour has been sieved for 72%, type “1” for 80% and type “2” for 85%.
The decortication process also occurs on this occasion but, in contrast to cylinder grinding, this process is milder as it preserves the germ and part of the bran. Even when semi-whole wheat flour is produced, the resulting colour always tends to be pale brown.
The wheat enters through a hopper; the grinders are two overlapping, special stone wheels that grind the wheat and the flour passes through a sieve called “buratto”, which divides bran from middlings. The two grindstones rotate in opposite directions and the grain is wholly milled, without separating its different parts.
The germ and essential oils in the grain of wheat are kneaded with the starchy part, giving flour an ivory colour with dark beige spots: this provides more complex fragrances, more taste and preservation of many of the healthy properties of wheat.
The benefits of this grinding method are mostly due to the reduced speed of the moving wheel that keeps the temperature low during the milling process and avoids any risk of overheating, thus preserving the organoleptic properties of the flour.
Whole wheat flour has not been sifted, so it still contains bran and its sifting percentage is 100%. Flour with a lower sifting rate is white, soft and rich in starch. Flour with a higher sifting rate, by comparison is darker and contains more fibres, vitamins, protein, fat and enzymes, substances that are all contained in the outer layer of the grain. It is a product less suitable for bread-making, but with a higher biological value.