Patent Description:
From the prior art, food pasta drying methods are known the object of which is to eliminate progressively from the product part of the initial water content, by administering heat, to lower the degree of humidity of the product. Lowering the degree of humidity means reducing enzyme activity, thus minimizing fermentation.

Drying can be provided in plants provided with suitable sources of heat that heat a mass of air that is subsequently sent into contact with the pasta to be treated to heat the pasta so as to evaporate progressively the humidity contained therein.

The steps of hot-air drying process are normally three: a first pre-drying step, a second drying step proper and a third stabilization step.

In the first pre-drying step, the pasta coming from a kneading apparatus and drawn through a drawing apparatus is in a plastic state, thus with the possibility of being deformed. In this first step, the pasta is heated rapidly with a great contribution of heat so as to reach the maximum obtainable value of the Q/t ratio without damaging the pasta, where Q/t is the quantity of humidity removed from the pasta per weight unit in the time unit.

The pre-drying step can be provided with a continuous pre-drying apparatus in which the pasta moves at a constant speed inside the apparatus and is hit by a continuous flow of hot air with a low level of humidity, coming from a heat exchanger. The flow of hot air causes heating of the pasta to evaporate the humidity that is contained in the pasta and to transfer the humidity to said flow of air.

The heat is transferred to the pasta in two modes: by convection from the flow of hot air to the surface of the pasta and by conduction from the surface to the inside of the pasta.

Also the transfer of humidity from the pasta to the flow of hot air that flows over the pasta occurs in two different modes: by diffusion from the inner layers of the pasta to the surface and by evaporation from the surface of the pasta to the flow of hot air.

At the end of the pre-drying step, the pasta is no longer in a plastic state, but in an elastic state. This means that temperature differences inside the pasta can cause internal tensions that, when they reach high values, may cause permanent deformation and also breakage in the pasta.

In order to avoid the occurrence of excessive tensions in the mass of pasta, during the drying step the transfer of heat from the flow of hot air to the pasta occurs more slowly, so that excessively high gradients are not created inside the pasta. This means that the humidity is removed from the pasta more slowly than in the pre-drying step. If with Q<NUM>/t the quantity of humidity is indicated that is removed from the pasta per weight unit in the time unit during the drying step, this quantity is less than the quantity Q/t removed in the pre-drying step, i.e. Q<NUM>/t<Q/t.

Also the drying step can be provided in a continuous drying apparatus that, normally, extends in height. The pasta is moved inside the apparatus from top to bottom whilst a flow of hot and dry air moves from bottom to the top.

In order to avoid drying defects it is important for the speed of the air inside the drying apparatus to be as constant as possible.

The drying step is deemed to be concluded when the residual humidity of the pasta does not exceed <NUM>%, which is the maximum humidity value for dry pasta set by law.

At the end of the drying step, the pasta is subjected to a so-called stabilizing step, such that the humidity percentage is uniform throughout the mass of the pasta, in order to avoid, despite total residual humidity not being greater than <NUM>%, the possibility of there being zones in the mass of the pasta with residual humidity greater than said value.

In the stabilization step, the pasta is maintained at a temperature above ambient temperature for a set time, at the end of which possible humidity gradients inside the mass of the pasta are zeroed.

Lastly, the pasta is cooled down to ambient temperature, to be subsequently packaged.

It should be noted that when the pasta is still in a plastic state, i.e. in the initial step of the drying process previously defined as pre-drying step, the transfer of humidity from the pasta to the flow of hot air depends essentially on the inner conditions of the drying apparatus, i.e. on the speed, temperature and humidity of the flow of air that hits the pasta. On the other hand, when the pasta has changed from the plastic state to an elastic state, at the end of the pre-drying step, the transfer of humidity from the pasta to the flow of hot air depends essentially on the diffusivity of the humidity inside the mass of the pasta.

The diffusivity of the humidity inside the pasta decreases as drying proceeds, which entails an inevitable extension of drying time.

In the drying processes with a flow of hot air that are known from the prior art, in order to reduce drying time, it has been proposed to raise the temperature of the flow of hot air up to about <NUM>. But this entails the risk of damage to the proteins and to the amino acids contained in the pasta, with a resulting reduction of the nutritional value of the pasta that is greater the greater the temperature is of the air used in drying the pasta.

By using a high drying air temperature, comprised between <NUM> and <NUM>, drying time can also be reduced to merely <NUM>-<NUM> hours, but pasta with low nutritional quality is obtained because of the changes to the gluten, to the proteins and to the amino acids caused by the high drying temperature.

Pasta of high nutritional quality is obtained by slow drying at a temperature that is not greater than <NUM>° C that damages neither gluten, protein or the amino acids contained in the pasta. But this entails long drying times, of the order of even <NUM>-<NUM> hours.

The processes of drying food pasta with hot air known from the prior art entail a significant expenditure of energy, which is necessary for heating the air and low energy efficiency, comprised in an interval between about <NUM>% and <NUM>%.

Further, the food pasta is not dried uniformly throughout the whole mass of the pasta, because heating is not uniform throughout the mass because the most external parts of the pasta are subjected to more intense heating than the most internal parts, with consequent non-uniformity in the features of the end product.

Lastly, it should be noted that drying food pasta by hot air requires different drying apparatuses for long pasta and for short pasta, with significant increased costs of making plants that can produce both long pasta and short pasta. U <NUM><NUM><NUM> A relates to the rapid drying of pasta whilst maintaining quality by using microwaves to complete the final step of drying to between <NUM> to <NUM>% moisture.

One object of the present invention is to provide a method of producing dry pasta, obtained from durum wheat flour, from soft wheat flour, or from mixtures of durum wheat flour and soft wheat flour, which enables the time to be reduced that is required for drying the pasta without there being alterations to the gluten, the proteins and the amino acids contained in the pasta, so as to obtain a pasta of high nutritional quality in a significantly shorter time than that required by drying with hot air at a low temperature not above about <NUM>.

Another object is to provide a method for drying food pasta that enables a product with uniform features throughout the mass thereof to be obtained.

A further object is to provide a method for drying food pasta that enables the energy consumption to be reduced that is required per unit of mass of dried food pasta.

A still further object of the present invention is to provide an apparatus for producing dry pasta according to the method of the present invention that is usable for producing both long and short pasta and has reduced operating costs.

The objects of the invention are achieved by a method for producing dry pasta according to claim <NUM> and with an apparatus for producing dry pasta according to claim <NUM>.

Owing to the invention, it is possible to dry the pasta in a short time by maintaining the temperature of the pasta at values that do not damage the gluten, the proteins and the amino acids contained in the pasta.

It is further possible to obtain substantially uniform heating throughout the mass of the pasta, which enables the stabilization step to be eliminated that is requested in hot air drying plants.

Owing to the invention, it is possible to reduce considerably energy consumption per unit of mass of dried pasta, with significant production cost savings.

Further, there is little heat dispersal to the environment that surrounds the apparatus for producing pasta according to the invention and absence of smoke, steam and noise in the environment.

Further features and advantages of the invention will be clear from the following description of embodiments of the invention, which are purely by way of example and are non-limiting, with reference to the enclosed drawings in which:.

Below, the food pasta can be referred to for the sake of brevity as pasta.

According to the present invention, a method is provided for drying food pasta made from durum wheat flour, or from mixtures of durum wheat flour and soft wheat flour that comprises the following steps:.

During a first drying step, the pasta P is heated to a temperature that can be comprised between <NUM> and <NUM>, for a set time that can be about <NUM> hour.

After said first drying step, a second drying step can be provided in which pasta is maintained at a temperature comprised <NUM> and <NUM> for a further set interval of time that can be about <NUM> minutes.

During said first drying step and during said second drying step, a flow of air at ambient temperature can be sent to the pasta P to remove the humidity produced by evaporation of the water in the pasta P.

After said second drying step, the pasta P can be cooled by a flow of cooling air, until the temperature of the pasta is the same as the ambient temperature.

Before drying the pasta P, it is preferred to maintain the pasta P at a temperature above ambient temperature for a set time, such that residual humidity inside the pasta P is distributed as uniformly as possible in the mass of the pasta.

In the case of production of long pasta, before the start of the first drying step, it is preferred to subject the pasta P to a ventilation step, sending onto the pasta P a flow of air at a temperature comprised <NUM> and <NUM>.

The ventilation is used to dry the surface of the pasta P to reduce the plasticity thereof, in order to prevent the pasta being possibly elongated excessively through the effect of its own weight.

In one version of the method according to the invention, the pasta P is heated in an environment in which a vacuum comprised between <NUM> bar and <NUM> bar is created so as to be able to dry the pasta P at a temperature comprised <NUM> and <NUM> that is lower than the drying temperature at atmospheric pressure.

Drying in an environment at a pressure that is lower than atmospheric pressure permits operation at a reduced temperature maintaining unaltered the organoleptic properties of the pasta and further reducing drying time.

In <FIG>, <FIG> and <FIG> an apparatus according to the invention is illustrated for producing both long pasta, such as for example spaghetti, bucatini, mafalde, candele or any other type of long pasta, and short pasta, such as for example maccheroni, penne, fusilli, conchiglie and any other type of short pasta.

With reference to <FIG>, an apparatus <NUM> comprises a kneading and drawing device <NUM> that is able to produce both long pasta and short pasta, a first radiofrequency dryer <NUM> for drying long pasta, a second radiofrequency dryer <NUM> for drying short pasta, a first ventilating device <NUM> arranged after the exit of the first dryer <NUM>, for drying the long dried pasta exiting the first dryer <NUM>, a second ventilating device <NUM> arranged at the exit of the second dryer <NUM>, for drying the short dried pasta exiting the second dryer <NUM>.

The kneading and drawing device <NUM> comprises a decantation cyclone <NUM> into which the durum wheat flour or soft wheat flour is delivered. The decantation cyclone supplies a volumetric dosing device <NUM> that sends the durum and/or soft wheat to a centrifugal pre-kneading device <NUM> in which the durum or soft wheat is mixed with water to obtain dough from which the pasta will be obtained. The dough is made by mixing the durum or soft wheat, which normally has relative humidity comprised between <NUM>% and <NUM> %, with hot water between <NUM> and <NUM> in sufficient quantity to take the product's relative humidity to a value comprised between about <NUM>% and about <NUM> %.

From the pre-kneading device <NUM>, the wet dough enters a kneader <NUM> in which complete absorption of the water by the durum wheat flour or soft wheat flour occurs, to obtain the dough from which the pasta will be obtained. Kneading lasts for a period of about <NUM> minutes, at the end of which the dough obtained is sent, through an airtight valve <NUM>, to a vacuum tank <NUM>, in which the air is removed from the dough, by a suction pump, that maintains in the tank <NUM> a pressure between <NUM> bar and <NUM> bar, to make the pasta shiny and devoid of imperfections after drawing.

From the vacuum tank <NUM>, the dough can be sent to a first compression device <NUM> (<FIG>) that supplies a first drawing device <NUM> for producing long pasta, or the dough can be sent to a second compression device <NUM> (<FIG>), that supplies a second drawing device <NUM> for producing short pasta.

For producing long pasta, in the first compression device <NUM> the dough is pushed at pressure comprised between about <NUM> bar and about <NUM> bar through a drawing device by means of which a curtain of pasta units P is formed that are sent to a so-called stretching device, in which the pasta units P are drawn and positioned on support and conveying elements <NUM>, for example in the form of rods or barrels, on each of which a plurality of pasta units P is loaded. The support and conveying elements <NUM> are loaded on a first conveying device <NUM> by means of which the support and conveying elements <NUM> with the pasta units P are conveyed to the first dryer <NUM> and loaded on a second conveying device <NUM> that conveys the support and conveying elements <NUM> with the pasta units P along a first drying tunnel <NUM> obtained inside the first dryer <NUM>.

Before entering the first drying tunnel <NUM>, the pasta P passes through a third ventilation device <NUM> in which the pasta is ventilated with air at a temperature comprised between about <NUM> and <NUM> to cause light drying of the outer surface of the pasta P, so as to reduce the plasticity thereof so as to prevent the pasta P undergoing excessive elongation because of its own weight.

In the first drying tunnel <NUM>, pairs of electrodes <NUM>, <NUM> (<FIG>) are distributed in a substantially uniform manner between which an electromagnetic field is generated oscillating at a frequency comprised between <NUM> and <NUM>. The pasta P, by traversing the electromagnetic field between the pairs of electrodes <NUM>, <NUM>, is heated. The power applied to the electrodes to generate the oscillating magnetic field is adjusted so that the pasta is heated to a temperature comprised <NUM> and <NUM>.

After a set interval of time of about an hour has elapsed, the power applied to the electrodes is reduced so as to reduce the temperature of the pasta P to a value comprised between about <NUM> and about <NUM>, maintaining the pasta at this temperature for a further set interval of time of about another <NUM> minutes at the end of which the pasta will be dried, i.e. with a humidity percentage not greater than <NUM>%, as required by legal standards. The expressions "about an hour" and "about <NUM> minutes" mean that said set interval of time and said further set interval of time can vary according to the size and thickness of the pasta P. In particular, said set interval of time is equal to <NUM> hour ± <NUM>% and said further set interval of time is equal to <NUM> minutes ± <NUM>%.

At the end of drying, the pasta P exits the first dryer <NUM> and is conveyed through the first ventilating device <NUM>, in which the pasta P is cooled to ambient temperature.

Subsequently, the pasta P is conveyed to a removing and cutting device <NUM> in which the pasta units P are removed from the support and conveying elements <NUM> and cut to a standard length for packaging, equal to about <NUM>. From the removing and cutting device <NUM>, the pasta P is then sent to a packaging apparatus (not illustrated).

For producing short pasta, the dough coming from the vacuum tank <NUM> is sent to the second compression device <NUM> into which the dough is pushed, at a pressure comprised between about <NUM> bar and about <NUM> bar, through the second drawing device <NUM>, exiting from which the dough is cut into a plurality of units of short pasta by a cutting device, which is not shown. The drawing device <NUM> is interchangeable, depending on the type of short pasta that has to be produced.

The short pasta that is thus produced is sent to a screening device <NUM>, known as "trabatto", in which the units of short pasta are separated from one another and dropped onto a fourth conveying device <NUM> by means of which the units of short pasta are conveyed to the inlet of the second dryer <NUM> where they move to a fifth conveying device <NUM> that transports the units of short pasta through a second drying tunnel <NUM> obtained inside the second dryer <NUM>.

Also in the second drying tunnel <NUM> pairs of electrodes <NUM>, <NUM> are distributed in a substantially uniform manner, between which an electromagnetic field is generated oscillating at a frequency comprised between <NUM> and <NUM>. The pasta P is heated by traversing the electromagnetic field between the pairs of electrodes <NUM>, <NUM>. The power applied to the electrodes to generate the oscillating magnetic field is so adjusted that the pasta is heated to a set temperature comprised <NUM> and <NUM>.

The pasta P is maintained at the aforesaid set temperature for a period of about an hour at the end of which the pasta P is dried and stabilized, at a humidity percentage that is not greater than <NUM>%, as required by law standards. The expression "about an hour" means that said set time can vary slightly depending on the size and thickness of the pasta P, in particular, said set time can be equal to <NUM> hour ± <NUM>%.

If special pasta types have to be produced, like nest pasta or lasagne pasta, the following procedure is followed.

In the case of nest pasta, the pasta that exits the drawing device is sent to a so-called "nesting" device <NUM> from which pasta exits with a shape that simulates a nest. Subsequently, the pasta that is thus produced is dried by the same method disclosed above for the long pasta.

In the case of lasagne pasta, the pasta exiting the drawing device is sent to a so-called "lasagnatore" device <NUM> from which the pasta exits in the form of lasagne. Subsequently, the pasta that is thus produced is dried by the same method disclosed above for long pasta.

Heating the pasta by microwaves during drying has the advantage of obtaining very rapid and uniform heating of the pasta, with a gradient of about <NUM>/s. Further, unlike hot air drying apparatuses, there is no need to pre-heat the environment in which drying has to occur until the drying temperature is reached.

Further, no pasta stabilization step is necessary at the end of drying.

It is possible to obtain short drying time, of little more than an hour, maintaining drying temperatures of no more than <NUM> so as to minimize degradation of the nutritional and organoleptic features of the pasta and to obtain pasta of high quality.

Lastly, the energy efficiency of a drying apparatus according to the invention is comprised between about <NUM>% and about <NUM>%, compared with the energy efficiency of a hot air drying apparatus according to the prior art, which is comprised between about <NUM>% and <NUM>%. This permits a great saving in the operating costs of an apparatus according to the invention.

In <FIG>, <FIG> and <FIG>, a variant la of a drying apparatus 1a is illustrated.

The drying apparatus 1a differs from the apparatus <NUM> illustrated in <FIG>, <FIG> and <FIG> by the fact that the first drying tunnel <NUM> and the second drying tunnel <NUM> are maintained under vacuum. In order to maintain under vacuum the first drying tunnel <NUM>, the first dryer <NUM> is equipped with at least one first vacuum pump <NUM>. The second dryer <NUM> is equipped with at least one second vacuum pump <NUM> to maintain the second drying tunnel <NUM> under vacuum.

The elements of the apparatus 1a that are the same as corresponding elements of the apparatus <NUM> illustrated in <FIG>, <FIG> and <FIG>, are marked by the same reference numbers used in <FIG>, <FIG> and <FIG>.

With reference to <FIG> that relates to the part of apparatus la intended for producing long pasta, the pasta units P supported on the support and conveying rods <NUM> and coming from the third ventilation device <NUM> are introduced into a loading chamber <NUM> of the first dryer <NUM>. The loading chamber <NUM> is equipped with a first sliding baffle <NUM> placed at the inlet of the loading chamber <NUM> and with a second sliding baffle <NUM> placed at the outlet of the loading chamber <NUM>. Said first sliding baffle <NUM> is movable between an open position in which it places the loading chamber <NUM> in communication with an outer environment at atmospheric pressure and a closed position in which it hermetically isolates the loading chamber <NUM> from the outer environment. The second sliding baffle <NUM> is movable between an open position, in which it places the loading chamber <NUM> in communication with the first drying tunnel <NUM>, and a closed position in which it hermetically isolates the first drying tunnel <NUM> from the loading chamber <NUM>. The second sliding baffle <NUM> is normally in a closed position in order to maintain under vacuum the first drying tunnel <NUM> of the first dryer <NUM>. The loading chamber <NUM> is further equipped with a third vacuum pump <NUM> that is intended to create a vacuum inside the loading chamber <NUM>.

The support and conveying elements <NUM>, each of which carries a plurality of long pasta units P, are introduced in groups into the loading chamber <NUM>, each group G1 comprising, for example, from <NUM> to <NUM> support and conveying elements <NUM>. During the introduction of the support and conveying elements <NUM> to the loading chamber <NUM>, the first sliding baffle <NUM> is in the open position to enable the rods <NUM> to be introduced, whilst the second sliding baffle <NUM> is in the closed position.

After a group G1 of support and conveying elements <NUM> has been introduced into the loading chamber <NUM>, the first sliding baffle <NUM> is moved to the closed position, sealingly hermetically the loading chamber and the third vacuum pump <NUM> is started to create in the loading chamber <NUM> a vacuum comprised <NUM> bar and <NUM>. <NUM> bar, substantially the same as the vacuum that is created and maintained in the first drying tunnel <NUM> of the first dryer <NUM> by the first vacuum pump <NUM>.

When the pressure in the loading chamber <NUM> is the same as the pressure inside the first drying tunnel <NUM> of the first dryer <NUM>, the second sliding baffle <NUM> is opened to deliver to the first drying tunnel <NUM> the group G1 of support and conveying elements <NUM>. After delivering the group G1 of support and conveying elements <NUM> to the first drying tunnel <NUM>, the second sliding baffle <NUM> is returned to the closed position, to seal the first drying tunnel <NUM>, then air is delivered to the loading chamber <NUM> to restore therein pressure equal to atmospheric pressure and the first sliding baffle <NUM> is taken to the open position, to be able to deliver to the loading chamber <NUM> a new group G1 of support and conveying rods <NUM> with the respective pasta units P.

The pasta P inside the first drying tunnel <NUM> moves between the pairs of electrodes <NUM>, <NUM> between which an electromagnetic field is generated oscillating at a frequency comprised between <NUM> and <NUM>. The pasta P, by traversing the electromagnetic field between the pairs of electrodes <NUM>, <NUM>, is heated. The power applied to the electrodes to generate the oscillating magnetic field is adjusted so that the pasta is heated to a temperature comprised <NUM> and <NUM>. Owing to the vacuum maintained in the first drying tunnel <NUM>, which promotes evaporation of the humidity contained in the pasta, it is possible to dry the pasta P at a significantly lower temperature than the temperature at which the pasta P is dried in the drying apparatus <NUM> illustrated in <FIG>, <FIG> and <FIG>, which enables the organoleptic properties of the pasta to be maintained substantially unaltered, because the temperature used during drying of the pasta in the first vacuum drying tunnel <NUM> is lower than <NUM>, the temperature at which the gluten, the proteins and the amino acids of the pasta start to degrade. This enables pasta of very high quality to be obtained.

The dwell time of the pasta P in the first drying tunnel <NUM> is about an hour, in particular <NUM> hour ± <NUM>%, at the end of which the pasta will be dried and stabilized, with a humidity percentage not greater than <NUM>%, as required by legal standards.

The first dryer <NUM> is equipped, at the outlet of the first drying tunnel <NUM>, with an unloading chamber <NUM> through which the dried pasta P can be unloaded from the first drying tunnel <NUM> to an outer environment at atmospheric pressure.

The unloading chamber <NUM> is equipped with a third sliding baffle <NUM> placed at the inlet of the unloading chamber <NUM> and with a fourth sliding baffle <NUM>, placed at the outlet of the unloading chamber <NUM>. The third sliding baffle <NUM> is movable between an open position, in which it places the first drying tunnel <NUM> in communication with the unloading chamber <NUM>, and a closed position in which it hermetically isolates the unloading chamber <NUM> from the first drying tunnel <NUM>. The fourth sliding baffle <NUM> is movable between an open position, in which it places the unloading chamber <NUM> in communication with the outer environment, and a closed position in which it hermetically isolates the unloading chamber <NUM> from the outer environment. The third sliding baffle <NUM> is normally in the closed position to maintain the vacuum inside the first drying tunnel <NUM>. The unloading chamber <NUM> is further provided with a fourth vacuum pump <NUM> that is intended to create a vacuum inside the unloading chamber <NUM>.

In order to unload from the first drying tunnel <NUM> a group G2 of support and conveying elements <NUM> with the respective dried pasta units P, the fourth baffle <NUM> is placed in the closed position, maintaining in the closed position the third baffle <NUM>, then the fourth vacuum pump <NUM> is started up to create inside the unloading chamber <NUM> a vacuum equal to the vacuum inside the first drying tunnel <NUM>. When the pressure in the unloading chamber <NUM> is equal to the pressure in the first drying tunnel <NUM>, the third sliding baffle <NUM> is placed in the open position and a group G2 of support and conveying elements <NUM>, with the respective pasta units P, is introduced inside the unloading chamber <NUM>. Subsequently, the third baffle <NUM> is returned to the closed position sealing the first drying tunnel <NUM>, air is delivered to the unloading chamber <NUM> to restore therein a pressure equal to the atmospheric pressure and the fourth sliding baffle <NUM> is brougth to the open position, to be able to extract from the unloading chamber <NUM> the group G2 of support and conveying elements <NUM> with the respective dried pasta units P and send the support and conveying elements <NUM> to the removing and cutting device <NUM> in which the pasta units P are removed from the support and conveying elements <NUM> and cut to a standard length for packaging, equal to about <NUM>. From the removing and cutting device <NUM>, the pasta P is then sent to a packaging apparatus (not illustrated).

Owing to the relatively low temperature at which drying of the pasta occurs, it is possible to do without the first ventilating device <NUM> for drying the pasta P and let the pasta cool spontaneously. It is nevertheless possible to use the first ventilating device to accelerate cooling of the pasta.

With reference now to <FIG>, relating to the part of apparatus intended for producing short pasta, the short pasta coming from the drawing device <NUM> is sent to the screening device <NUM>, known as "trabatto", in which the single units of short pasta are separated from one another and dropped onto the fourth conveying device <NUM> by means of which the units of short pasta are conveyed to a loading device <NUM>, <NUM>, <NUM> by which the units of short pasta are delivered to the second drying tunnel <NUM> of the second radio frequency dryer <NUM>, inside which a vacuum is made comprised between <NUM> bar and <NUM> bar by the second vacuum pump <NUM>.

The loading device <NUM>, <NUM>, <NUM> comprises a loading hopper <NUM> into which the units of short pasta coming from the fourth conveying device <NUM> are delivered; the loading hopper <NUM> communicates below with a sealed first star valve <NUM> by means of which the units of short pasta are delivered to a zig-zag chute <NUM> that communicates with the second drying tunnel <NUM>. The units of short pasta drop by gravity along the zig-zag chute <NUM> that slows the fall and join the fifth conveying device <NUM> to be conveyed along the second drying tunnel <NUM>.

The units of short pasta move between the pairs of electrodes <NUM>, <NUM>, between which an electromagnetic field is generated oscillating at a frequency comprised between <NUM> and <NUM>. The pasta P, by traversing the electromagnetic field between the pairs of electrodes <NUM>, <NUM>, is heated. The power applied to the electrodes to generate the oscillating magnetic field is adjusted so that the pasta is heated to a temperature comprised <NUM> and <NUM>. Owing to the vacuum maintained in the second drying tunnel <NUM>, that promotes evaporation of the humidity contained in the pasta, it is possible to dry the pasta P at a significantly lower temperature than the temperature at which the pasta P is dried in the drying apparatus <NUM> illustrated in <FIG>, <FIG> and <FIG>, which enables the organoleptic properties of the pasta to be maintained substantially unaltered, because the drying temperature of the pasta in the second vacuum drying tunnel <NUM> is lower than <NUM>, the temperature at which the gluten, the proteins and the amino acids of the pasta start to degrade. This enables pasta of very high quality to be obtained.

The dwell time of the pasta P in the second drying tunnel <NUM> is about an hour, in particular <NUM> hour ± <NUM>%, at the end of which the pasta is dried and stabilized, with a humidity percentage not greater than <NUM>%, as required by legal standards.

The second dryer <NUM> is equipped with an unloading device <NUM>, <NUM>. <NUM> which enables the dried pasta to be unloaded from the second vsauum drying tunnel <NUM> to an environment at atmospheric pressure. The unloading device <NUM>, <NUM>, <NUM> comprises an unloading hopper <NUM> communicating with the second drying tunnel <NUM>, into which the fifth conveying device <NUM> delivers the now dried units of short pasta. The unloading hopper <NUM> communicates below with a second zig-zag chute <NUM> through which the units of short pasta reach by gravity a second sealed star valve <NUM> that unloads the units of short pasta onto an outlet chute <NUM> in an environment at atmospheric pressure, for subsequent tranfer to a packaging apparatus (not illustrated).

In <FIG> a pair of electrodes <NUM>, <NUM> is illustrated by means of which an electromagnetic field oscillating at a frequency comprised <NUM> and <NUM> is applied to pasta units P that transit between the electrodes.

The electrodes are supplied by a generator <NUM> of oscillating magnetic field, connected to the pairs of electrodes <NUM>, <NUM> by coaxial cables <NUM> that are shielded to avoid interference with the electromagnetic field generated by the generator <NUM>, the lines <NUM> of which are shown in <FIG>. In <FIG> the humidity that exits from the surface of the pasta P through the effect of the heating caused by the oscillating magnetic field is symbolized by the small arrows, which are indicated by the reference number <NUM>.

In <FIG> the generator <NUM> of oscillating magnetic field is schematized. The generator <NUM> is supplied with direct current by a rectifier <NUM>, which is in turn supplied by a normal alternating current grid <NUM>, for example <NUM> V at a frequency of <NUM>. The rectifier <NUM> supplies a circuit <NUM> generating an oscillating electromagnetic field, which is connected to the pairs of electrodes <NUM>, <NUM>. Between the circuit <NUM> generating an oscillating magnetic field and the pairs of electrodes <NUM>, <NUM> an impedance adapter circuit is interposed <NUM>, which results in the impedance seen from the generator <NUM> of oscillating magnetic field having a set constant value, to compensate for possible impedance variations of the load consisting of the pairs of electrodes <NUM>, <NUM> with the respective coaxial supply cables <NUM> and the pasta units that transit between the electrodes <NUM>, <NUM>.

The electrodes <NUM>, <NUM> of each pair of electrodes can be arranged aligned between themselves, as illustrated in <FIG>, or staggered, as illustrated schematically in <FIG> that shows a series of pairs of electrodes <NUM>, <NUM>, with the electrodes of each pair staggered in relation to one another. The pairs of electrodes are arranged in sequence along the path of the pasta P in the first drying tunnel <NUM>, or in the second drying tunnel <NUM>.

Claim 1:
Method for producing dry pasta comprising the following steps:
- preparing with durum wheat flour, soft wheat flour or a mixture of durum wheat flour and soft wheat flour and water a dough having humidity comprised between <NUM>% and <NUM>%;
- placing the dough in a chamber in which a vacuum between <NUM> bar and <NUM> bar is created; pushing the dough through a drawing device by applying to the dough a pressure comprised between <NUM> bar and <NUM> bar, to obtain food pasta (P) in the form of units of long pasta or units of short pasta;
- conveying and delivering said pasta (P) to a dryer (<NUM>, <NUM>);
- drying said pasta (P) in said dryer (<NUM>, <NUM>) until the humidity of the pasta (P) is not greater than <NUM>%, said drying comprising heating said pasta (P) in said dryer (<NUM>, <NUM>) to a set temperature and maintaining the pasta at said set temperature for a set interval of time;
- extracting said dried pasta (P) from said dryer (<NUM>, <NUM>);
characterized in that said heating is obtained by passing said pasta (P) inside an oscillating electromagnetic field having a frequency comprised between <NUM> and <NUM>.