Unlike the shelling which is a procedure that is different for each grain, the milling process is the same with all grains. Only the machine settings differ.
Besides the traditional methods (using mortar and pestle, grinding wheel) that are still used in rural Africa, small mills have appeared in the cities, and then in the villages.
This section deals with the general aspects of the milling technique, and presents the different non-industrial technical solutions adapted to rural and urban zones in developing countries.
The products of the milling[edit | edit source]
Cereals are the basis for many dishes, specific to each region: couscous, tortillas, dumplings, ... The flour, meal and breaked rice resulting from the grinding and milling and sometimes a fermentation of the hulled grains. It is in these forms that grains are used in cooking, it is indeed very unusual to see one consume whole grains, except in the case of rice.
The particle size
The milled products are distinguished by the fineness of the particles: the particle size.
For the best quality flour, the particle size is less than 0.2 mm; for flour "for rolling" or for "couscous" flour, the size varies from 0.2 to 0.7 mm; for meal between 0.7 and 1 mm; for thin broken maize between 1 to 1.5 mm; for average broken grain from 1.5 to 2.5 mm, and finally, the large broken grains are smaller than 2.5 mm. These products are obtained in most cases by a dry process and present a low final moisture content (below 10%) that ensures a long shelf life.
In industrial milling installations, the grains are ground in several stages, the fine, medium and large particles are separated using a sieve in each stage. The same thing happens in the traditional grinding by pestle, where the grinded matter repeatedly passes through a sieve. Thus, only large particles continue being crushed. Regarding the mills described here, a high degree of grinding is generally obtained by several passings in the mill, but without sieving.
For a general assessment on the fineness of the grinded matter of a mill or on the grinding process we need a certain method for measuring, because flowers are not homogeneous. They are indeed made of particles of different sizes (an average meal produced by a "simple" mill or by a traditional process, has 80% (by mass) of the particles having a size ranging between 0.1 and 1 mm).
Image 7 describes the used measuring method in determining the flour smoothness index: a series of standard sieves separate the mixture into five classes of particles. Their share of the total mass (eg 100 grams) of the sample is multiplied by the weight factor. The sum of the five results constitutes the index of smoothness.
The higher the smoothness index, the lesser the flour is fine. The common flour fineness in Africa is between 1 and 2.
Various uses depending on country
The flour is usually used for the manufacturing of porridge ("rouy" in Senegal) or paste ("tô" in Burkina Faso). It is sometimes used for the home preparation of rolled products such as couscous, but the low humidity often makes this difficult.
Broken rice or finely broken millet, sorghum or maize is used for the preparation of dumplings. It can also be used for certain dishes: meal cooked in a vegetable and fish broth, steamed meal served with a sauce, ...
Broken maize is also used for the preparation of dumplings and salted dishes inspired on rice dishes. They are also sold to breweries.
Wet or dry flour?
The grain moisture, and thus the flour, plays an important role in its shelf life, in the choice of the grinding equipment, and the taste of the finished product.
The drier a flour is, the better it keeps. The tolerable limit of humidity is 16%. The meal prepared by the African women with hulled millet with the pestle and mortar (ie wetted), only keeps for one or two days, and then fermented unless the grain has been dried after the shelling. This wet grain, which is made by the women grinders, has a slightly fermented charisteristic and it is a popular flour in Africa.
The mill must be chosen according to this constraint (not all models are capable of grinding wet grain), or we must insert an extra drying step between wet and dry milling. Seeing that the women frequently use grinders, this change in traditional practices does not appear to be a constraint.
Other quality criteria
The quantity of brans and impurities in the flour is also a criterion of quality. Some traditional African dishes can tolerate a meal with a bit of brans, however other dishes, like certain dumplings or the manufacturing of traditional pastes require very pure flour.
The quality of the vitamins and proteins in the flour is also an important criterion, especially for the manufacturing of children flours whose nutritional value and composition should be correctly determined.
Of these, two books are particularly recommended: " Transformer les céréales pour les nouveaux marchés urbains, Broutin Cécile, Collection Le Point Sur AGRIDOC & GRET, Paris, France, 2003, 296 p. ISBN : 2-86844-142-4"; and "Précis technique sur les farines composées, application des techniques existantes, available on-line at: http://web.archive.org/web/20190205200642/http://www.fao.org:80/Wairdocs/X5033F/X5033f00.htm
