Hot air has a far greater capacity to absorb moisture than cold air, which is why the drying process of fruit and vegetables, as natural as it is, takes place best at temperatures that are warm but below those that would lead to the cooking of food (i.e. between 40 and 60 degrees, on average). The heat pump is a very advantageous system, in energy terms, for producing hot air, but it is most advantageous when a very high temperature difference is not required. In the case of drying, where a temperature close to 60 degrees optimises the process by greatly limiting oxidative and enzymatic processes, the heat pump alone is often not sufficient and an additional heating element is required. In addition, the heat pump is a very expensive device, requiring much more maintenance than the electric heating element, and more delicate. It can only be cost-effective, at a much higher purchase price all other things being equal, for particular, very delicate products that require very low drying temperatures, lower even than ambient temperatures. It should also be considered that both heat pump dryers with a dehumidification process, which work at temperatures below 20 degrees or even close to zero, and generically all those that do not reach cooking temperatures (to distinguish them from industrial processes in which even 100 degrees are exceeded and the product is, in fact, cooked) are often referred to as 'cold dryers'.

The actual loading capacity of a dryer is affected by many factors. The overall volume of the drying chamber, which is sometimes quoted, is perhaps the least important, because very few products can be loaded, when fresh, by filling the volume evenly without creating preferential air paths. It is therefore better, even in the case of herbs and medicinal plants, to have the possibility of arranging the products in boxes for better and safer distribution and more uniform air passage. All other products such as fruit, vegetables, but also meat and the like, on the other hand, require large surfaces in which to distribute a layer (slices, pieces or puree) that is as even and not too thick as possible. It is therefore much more important to evaluate the overall drying surface than the volume. But surface area and volume tell us how much we can load, not how much the dryer will be able to handle. In fact, drying capacity depends on power and the ability to process and dispose of moisture. This is why it is important to understand the power and disposal operation, otherwise the dryer will not be able to handle the moment of maximum humidity, in the first hours of the process, greatly increasing the risk of mould and contamination. This is why two dryers in the Tauro catalogue that have equal volume and equal surface area (B.Master Plus and P.Master Plus Twin) have such different capacities. In the case of mushrooms and aromatic herbs, the power is sufficient for both, and therefore the drying capacity depends only on the volume and surface area; in the case of heavier, water-rich products such as tomatoes, it can be seen how the Twin model's double power and disposal capacity leads to a much higher capacity.

Consumption depends on various parameters, and not only on the product to be dried. Certainly, however, the more water-rich a product is, the more energy it will need to be dried, because water needs large amounts of energy to evaporate. A good management of humid air, able to dispose of a lot of it when the product is fresh and less later, is certainly a good basis for optimising consumption while maintaining a good result. Air recirculation, with the possibility of disposing of the humid air only when necessary and keeping the still fairly dry air in circulation instead, is the device that saves the most. Other heat recovery systems (recuperators, or closed circuit heat pumps) can have even better efficiencies but at a much higher cost and a much more complex machine, also in terms of maintenance.

For the water to evaporate from the surface of the products, it must be lapped by dry moving air. If I overlap the slices, I create a plug that does not allow drying except in a much longer time, jeopardising the good quality of drying. Overlapping the slices without spacing them properly is a mistake. Some types of product can be dried in several layers (doubling or sometimes even tripling the surface area of the dryer) using special non-stick nets, as long as they are structured in such a way as to always guarantee a minimum exchange of air.

Dehumidifying humid air, keeping it circulating or not, can be achieved by using a heat pump or other systems (e.g. with hygroscopic salts). These are almost always delicate and very expensive systems, which also entail problems related to the risk of contamination and proliferation of micro-organisms on the exchangers where condensation takes place (which should therefore be made of stainless steel, and therefore less efficient than aluminium ones, and sanitised almost daily).

Cold drying is a term used in various contexts with often different meanings. While in scientific and laboratory environments there are certainly cold dryers that work at temperatures close to zero, and for some pharmaceutical products this can be an advantage, it is also true that in general, considering the very low efficiency of such cold air in absorbing moisture, processes in which one works at room temperature or within 40 degrees are also considered 'cold'. Similarly, 'low-temperature drying' and 'hot-air drying' often have various meanings. Certainly, drying systems at temperatures of even more than 100 degrees are used in industry, and therefore all those working indicatively between 40 and 60 degrees can be considered 'low-temperature dryers'. But more generally than temperature, it would make sense to consider the result. A lower temperature does not always lead to a better result, in fact due to higher enzyme activity the opposite is often true! We at Tauro have dried hundreds of different products, receiving feedback not only from the many professionals, but also from the tens of thousands of customers who use our dryers for domestic use.