In these systems, the food puts in contact with a plate, a liquid or a metal band from which the thermal transmission by conduction will be carried out (contact between solids). These devices ensure a short freezing time provided that the product is a good heat transmitter and its thickness is not excessive (less than 50-60 mm). It is very important that throughout the freezing process a close contact is maintained between the product and the freezing surface. Three types of freezers are distinguished by direct contact: of plates, bands and rotating drum.

Air is the most common freezing system.

It should be made clear that a frozen preservation chamber should not be considered a freezing system. The freezing rates achieved in the chamber are very small, so the quality of the products obtained will always be low.

Air freezing in good conditions is carried out in equipment specially designed for this purpose, such as freezing tunnels, conveyor belt freezers and fluidized bed freezers. In all cases, evaporators are used through which a cooling medium circulates (such as ammonia), the air passes through the evaporators, cools and in this way passes through the product, carrying out the phenomenon of freezing.

These systems do not need to be connected to a mechanical cold production system. The heat transfer medium is generally liquid nitrogen, stored in the vicinity of the equipment.

The cryogenic alternative offers maximum advantages for small capacity installations or for the initial production of new products, since its high operating costs will not allow its use for most products.

Liquid nitrogen freezers can be found that work by immersion or by spraying the cryogenic liquid.