When the wheat arrives, it has to be checked through an accurate inspection.
Analyses are carried out on a homogenous sample which is obtained through probes in different areas and at different depths. Only after these chemical legal and qualitative tests can wheat be delivered in the pit. The pit is made up of reinforced concrete and is topped by a grid where the lorries unload cereals. At the basis of the pit a cochlear system and a Redler system convey wheat to the bucket elevator which will take wheat to the pre-cleaning machines.
This step is conceived for eliminating all non-usable noxious impurities such as stones, glass fragments, iron or ash. The machines which are involved in this process are the balance, the magnetic separator and the winnower linked to an aspiration system with cyclones and filters.
The magnetic separator has two functions: eliminating the ferrous material which comes from the outside and eliminating screws or bolts which can be lost during processing. The separator helps eliminating the impurities by using a sift. In modern separators, there are 2 parallel sifts, the former for greater impurities and the latter for littler impurities such as sand or ash.
There is a vibrating system. The winnower is conceived for aspiring the lightest particles in wheat. Sometimes there is only an aspiration system; sometimes the winnower has an air recycling system (or with expansion chamber) linked to decanters and filters. The winnower is generally associated to the separator, but it can also be left alone.
In general, wheat enters a space where there is an ascending airflow that draws all the lightest particles such as straws and so on.
The most recent machines have an air-recycling system which eliminates the need of cyclones and filters. In this case, the air is separated from the product thanks to the internal decanter. Winnower without internal decanters must be linked to cyclones that allow separating particles and air.
After eliminating all impurities, wheat is stocked for a period and transported to first-cleaning machines.
During this step, a de-stoner and a sifter are added. The first eliminates stones thanks to a vibrating movement, by using the specific weight of wheat and an airflow which moves wheat. The machine is made up of an inclined metallic grid which enables the air passage from the bottom to the top. The airflow is calibrated to keep the wheat on top. Stones and gravel which are heavier remain on the bottom. The inclination of the surface make the stones going towards the higher part of the surface. The machine can be adjusted and inclined according to needs as well as the intensity of the airflow.
The de-stoner is linked to the aspiration system. The sifter has at least 2 or 3 cylinders. The first eliminates the long seeds (oat, barley, rye). The second eliminates round seeds (grains, vetches, corn). Vetches are leguminous. A third or a fourth cylinder can follow and are known as review cylinder. Each cylinder is made up of a rounded foil with holes; seeds having the same size of holes can pass and reach the higher part of the cylinder where they fall into a bowl and then outside the machine thanks to a cochlear system.
The magnetic separator acts thanks to a magnet; the separator acts per size; the de-stoner acts per weight and the sifter acts per shape.
Brushes are made up of a metallic fine-knit cylinder and a brush which allows eliminating all impurities on seeds (cortical parts or bacteria).
The efficiency is ensured by seeds’ rubbing against metal and the rubbing between seeds themselves. A winnower intervenes after the brushes.
Silos are usually vertical with steel cylindrical cells. Ventilation in cells is of the utmost importance. Here below the parameters to ensure a perfect conservation of wheat: humidity max 14%; temperature max. 27°C; air humidity max. 75%. In case of overheating, wheat can be transferred to another silo where temperature and humidity are lower.
During this step, wheat is prepared for grinding in two phases. First, wheat is humidified. Second, water penetrates into seeds. Conditioning is useful to have an elastic seed that water can penetrate reaching the cortical part to the flour almond.
This helps to plump seeds in order to facilitate bran detachment. At the same time, chemical phenomena occur, reducing starch in fermentable sugars and producing CO2 which helps the detachment. The increase in elasticity prepares wheat to grinding rolls. A good conditioning makes wheat permeable to water in a uniformed way. In this case, different white flours can be obtained given the lower percentage of ashes. Conditioning is carried out by a machine with mixer cochleae. During the first step a precise quantity of water is added to increase humidity from 12% to 14% (the percentage varies according to the different chemical and physical features of wheat and climate conditions). The machine consists of a metallic box where there is a cochlear system with pallets that are inclined so that wheat is moved with different speed.
First, there is a wetting system which nebulizes water on wheat. Wheat is mixed and allows water penetrating the single grain. At the right moment, wheat is destined to resting cells where it remains until humidity attains the inner part. There are usually multiple conditioning steps: 2/3 of water are nebulized during the first step, then 1/3 of time is dedicated to rest with the process ending in the resting cells for the time needed for all chemical and physical process to occur.
Wheat is now transformed into a finite product. All wheat is weighed and controlled with the percentage of humidity before arriving to the first grinding machine, named B1.
All wheat undergoes the first grinding and goes to the first Plansifter which divides it per size so that the following machines treat only some parts of products.
The grinding department is usually divided into three levels.
The B mills are destined to breaking, the C mills to regrinding, the D mills to undressing and the DD mills to dividing.
The 2 rolls have different speed which boosts cutting features for some rolls and crushing features for smooth rolls.
The highest speed is 6-8 m/s. The fastest roll is directly linked to the engine, the other is linked to the gear wheel that gives movement to the cylinder thanks to its larger diameter. The difference in speed determines a lower heating due to friction. The 2 rolls can have 4 positions: cut-cut, back-back, cut-back and back-cut. Cut-cut ensures the greatest pressing action. Cylinders have a swaging in the central part (20-40 microns). Some builders patented roll mills with two superposed rolls so that B1 and B3 can act in the same machine. Plansifter is aimed at classifying grains by size. Each Plansifter is suspended to the supporting wooden or fiberglass beams. The machine has an eccentric movement. The interior part is organized in light-superposed sifts. The expression luce di maglia indicates the size of the holes which can be measured in micron or on arbitrary scale marked with the letters XX or GG. Each sift is made up of wooden garnish which blocks the nylon as the metallic veiling.
Systems which improve the veiling functioning are called tip-top for their movement. The internal part is organized so that products for grinding enter the first sift which lets the smaller products pass. Waste is eliminated through a canal. This step is repeated at each passage, so there will be as many canals as the number of passages.
The semolina machines eliminate the bran parts and separate semolina. They are organized into horizontal sifts so that brans enter the hopper, gets to the first vibrating sift where it is separated by size and passes on to the other sift. A calibrated airflow goes from the bottom to the top and draws the bran parts. Given that sifts are horizontal, the first sift can have smaller holes.
This means that the resulting semolina is the finest one. In order to get the best results, the products need to be homogenously spread on the perfectly tightened sifts. The airflow must be homogenous too. The main values are therefore linked to the airflow setting. The only difference between the soft and durum wheat semolina machines lies in the size of holes and the number of machines in the grinding program.
The veiling is made up of nylon or silk and is placed in a wooden or fiberglass framework; its action is protected by a brushing system. The fundamental analysis is about ashes since they reveal the presence of brans. The other parameter to value the grinding is the size verification at each passage.
In order to meet clients’ needs that sometimes can be very different, it is necessary to produce diversified flours. This translates into flours that are not only high in quality but also adequate to all types of preparations. This explains the number of silos destined to numerous and different types of wheat.
When opting to produce a particular kind of flour, the miller sets the needed quantity of each material. The trend is to prefer high quantities of varieties so that a good final balance is ensured. When mixing grains, the desired quantity is took by volumetric dosers that send grains to the first cleaning.
The product is sent from the grinding department to the stores where there are numerous mixers. Indeed, since the flours are very different in colour and texture, mixing is necessary. There is also a smaller, but powerful Plansifter which has squared sifts with little-hole veiling which checks all flours arriving there. After this check, flours are sold in two ways: packed or mixed.
In the first case a machine takes the quantity needed, weighs the flour, and packs it. In the second case, flour is transported to boxes where it is taken from lorries.