We have some problems with the “trabatto” (pre-dryer) that we use at the pasteurizer exit both for fresh and dry pasta. Even if the operational temperature is 60° C and pasta remains in it as long as possible, when it comes out it’s still very moist. As a consequence, fresh pasta sticks to trays and to solve the problem we need to partially dry it in the dryer.The pre-dryer belongs to a technician we consulted to understand how to prevent pasta from remaining wet. He said it’s our fault, because our dough is too moist. But immediately after drawing, our pasta looks fine, and when we tried to make dough with less water, the results have been very poor, because the pasta surface was scratched and not uniform as it should be.
How can we solve this problem?
E.Z., Naples
It would have been useful to have some more information to better focus the problem and its causes. Such situations are quite common, so the answer, independently from E.Z.’ production strategy (e.g.: we do not know their machines capacity, the type of pasteurization or the actual transit time of pasta inside the pre-dryer) can be very interesting.
We can deduce how the pre-dryer is made from its type and brand – which obviously we will not mention – and this is the starting point to explain the origin of the problem.
At the start of the processing, the environment inside the pre-dryer is hot and dry because during the preheating with no load (we hope this step is always performed…) the ventilation with increasingly hot air reduced both the absolute and the relative humidity of the environment inside the machine.
When pasta enters the pre-dryer to be ventilated and heated, some of the water on its surface evaporates, thus increasing the humidity inside the machine. But how much? That’s the heart of the matter.
E.Z.’ pre-dryer is not equipped with a system for the extraction of moist air in excess, as it is completely closed except for the two windows for letting past in and out. Because of this kind of structure, moisture released by pasta doesn’t find an adequate way out and the internal atmosphere becomes more and more humid, until reaching the saturation point.
What does this mean? It means that when we reach this point, the evaporation of pasta – independently from the operational temperature of the pre-dryer – is completely interrupted. Therefore pasta comes out as moist as it was at the entry and, in case of further complications, it may exit even moister and wetter or tend to pile up or make blocks on the vibrating shelves of the pre-dryer.
What’s the solution? Manufacturers of pre-dryers who know how pasta has to be properly produced, equip their machines with windows provided with adjustable shutters allowing the modification of the vents through which the humid air that is inside the machine – having a higher pressure than the air of the pasta factory because the heat exchanger fans are working inside the pre-dryer – is sent out, thus keeping both the absolute and relative humidity levels stable.
This way, acting on the regulation shutters, the pasta maker can intervene on the process taking place inside the pre-dryer and obtain a packaging that meets his needs.
In addition to windows with adjustable shutters, bigger pre-dryers (for machines with capacities exceeding 150 – 200 kg/hour) are equipped with a forced extractor of moist air, because the more pasta you have, the more steam is released inside the pre-dryer; therefore only windows for the exhaust of moist air may not be enough to keep the proper balance of air relative humidity.
Obviously, windows with shutters and the extractor must be correctly positioned: the standard location is in the lower part of the machine, because it is the area where moist – and therefore heavier – air tends to concentrate.
In short, this is the adequate functional structure of a real pre-dryer, able to remove the surface humidity of pasta, at the well-known “wrapping”.
E.Z.’ pre-dryer is not equipped either with windows or with an extractor. Therefore its functionality is no doubt compromised, and is even more critical because pasta coming out of the pasteurizer can feature very high surface moisture.
So the solution in such cases is to do what the manufacturer has not: open windows with adjustable shutters or – and this is what we suggest to E.Z. because this is the most efficient solution – install an extractor of moist air outside the pre-dryer by means of a through tube in the side cover panel. The vent must be positioned inside in the lower part, next to the bottom and – most importantly – in an area where the air turbulence caused by the heat exchanger is lower. Normally this area is located at the opposite side of the exchanger, but it can be easily identified with an anemometer or with the old and simple method of the “moist hand”, to feel on the skin where the air is slower or even nearly still.
In the meantime, I suggest to E.Z. an emergency solution: loosen the fixing bolts of the side panels of the pre-dryer and leave an open space at the bottom, between the pre-dryer structure and the bottom of the panel, to create an opening for the exhaust of moist air that has not been provided for by the manufacturer. Surely, this is a “half solution” and a temporary one, but it will be enough to show what results can be achieved making the pre-dryer work properly. Good luck with your work.
