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In modern pasta factories, semolina, stocked in silos, is sent by pneumatic conveyers to the production area. The first operation in the pasta process line is mixing of the semolina with water. To 100 kg of semolina, with a humidity content of 10-14%, 22-30 kg of water are added. The humidity in the mixer varies between 30 and 35%, according to the quality and the type of semolina, and the format of pasta being produced.The continuous devices used for the weighing of semolina and the water control flow pumps are monitored by high precision instruments and regulated by microcomputers operating in a closed loop, so as to compensate automatically for any variation of metering of one of the components and thus to adhere to the mutual ratios pre-determined on the basis of the recipe.
It is important in this phase for the semolina to be well hydrated in a uniform way, without the forming of masses or lumps in the dough, which should remain of uniform consistency in order to permit the correct feeding of the extruder screw. A slight or not very uniform hydration, which may be caused by the wrong quantities of water or by insufficient working times, can lead to defects in the finished product, such as breaking of the dry pasta, surface defects and even poor cooking quality.
The mixing phase is completed once the mass has been appropriately degassed in the vacuum mixer. In fact, it is very important for the air present in the dough (and incorporated precisely as a result of the previous operation) to be removed, to avoid its presence causing, thereafter, the oxidation of the pigments of the semolina (or of the egg, in the case of egg pasta), and for the presence of air bubbles to confer on the finished product opacity and poor shine, the last being a quality of aesthetic value.
In the course of the extrusion phase, which is achieved as an effect of the thrusting action of a worm screw within a cylinder (cooled from outside), the dough comes to the extrusion chamber (the 'bell'), where under the physical action, the hydrated proteins interact forming the "gluten".
The dough is the extruded at pressures varying between 4 and 12 MPa through a bronze or steel die having an appropriate geometry both of the plate (circular for the short pasta formats and straight for the long pasta), and of the holes reproducing the cross-section of the pasta. If the holes of the die are faced with Teflon, a smooth pasta will be obtained, otherwise a pasta of rough appearance will be produced.
The pasta comes out of the die with a humidity content of about 30%. To confer on it a specific consistency and the possibility of long shelf-life conservation, without any alteration in the quality of its raw materials and in the ingredients used, it is necessary for the maximum water content limit to not exceed 12.5% at the end of the pasta production line.
Accordingly the extrusion followed by an operation of the utmost importance consisting of the drying by degrees of the product. How this is carried out determines the final quality of the pasta (suffice to consider that the 'holding' of cooking of the product may also depend on the duration and the temperature of drying).
This operation consists of three distinct stages:
- pre-drying
- central drying
- final drying.
Accordingly this first phase of drying takes place in relative by short time scales (between 10 minutes and one hour) in special ventilated and heated chambers, eliminating about 15-20% of the humidity present. This phase is not needed for long pasta since the latter is transported hanging from canes, and there is less danger of sticking and deformation.
The pre-drying is followed by a second phase known as "central drying". This involves a further drying of the product, by means of another hot airflow, followed in alternate phases by a phase of rest ("tempering") in order to permit the humidity remaining inside the pasta to be redistributed uniformly on the surface. In some pasta production line the “tempering” phase is not foreseen needed. During the “central drying” up to the 60 % of the humidity present is eliminated.
Finally the cycle of drying is completed with the last phase or "final drying" in chambers, undergoing several repetitions of passing through a powerful hot and dry air, that removes up to 25- 30 % of the initial humidity.
This last phase is carried out at variable temperatures, which may even exceed 80°C. The temperature and the duration of the cycle vary according to the type of technology employed and the type of pasta format, which call for different types of drying.
In practice the whole drying operation takes place on the basis of a continuous process that comprises pre-drying, central drying and final drying. Depending on the kind of production line, this operation can be performed in separate chambers or through an uninterrupted tunnel, but subdivided into three continuous stages.
In the drying phase, the pasta crosses the various stages conveyed on various planes of moving belt, including at differentiated speeds according to the time required for undergoing the various phases. In certain cases rotating drum dryers are used, explicitly dedicated to the short formats, with sectors in aluminium and grid in stainless steel placed right along the internal surface of the cylinder: the inside of these sectors consists of boxes separated by inclined planes, that during the rotation of the drum determine the advance of the pasta. The continuous line dedicated to long pasta is preceded by a further device (the "spreader") that serves to hold straight and at a certain distance apart the rows of pasta arriving from the extruder, followed by a loader of the "sticks" on which the rows of pasta bent into the shape of a "U" are set.
The drying tunnel has a series of tracks on superposed planes along which the canes are moved. The silos consist once more of a tunnel with several tracks along which the canes move until called up by the cutter that will cut up the 'elbows' of long pasta. A cane unloading device (the "stripper") has the task of unloading the pasta from the canes, cutting it in pieces about 25 cm long and of sending them to the loader, thus ensuring the continuity of the cycle. The production line for the lasagne, 'nest', 'tangle' and special formats also has an initial kneader as for the short pasta, but in addition specific machinery for shaping the pasta and a loader/unloader of frames on which the pasta is accommodated for the whole duration of the drying process.
At the end of the line a “cooling” chamber lowers the temperature of the dried pasta channelled to the stocking silos.
On completion of this last phase, the pasta may be sent to the lines for assembly. Primary packaging (in contact with the pasta) may be of two types: one using sheets of plastic material and the other cardboard boxes.
For egg pasta, the production cycle is no different from that for the other dry pastas, except for presence of an automatic measurer for the egg mixture. [150, Unione Industriali Pastai Italiani, 2002]
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