In conventional cooling, the cold acts on food from the outside,which happens very slowly. With vacuum cooling, the cooling process is transferred to the inside of the chilled food and is thus greatly accelerated. Pastries and vegetables stay fresh longer and the process becomes much more efficient.
Our refrigerators and cold-storage rooms in the food industry works according to the principle of extraction of heat through evaporation. In refrigeration machinery, a gaseous coolant is first transformed into its liquid state in a compressor using overpressure. Under normal atmospheric pressure it evaporates again and pulls heat from the refrigerator compartment. Anything placed inside then takes on the cold temperature of the refrigerator over time. This initially happens on the surface of the chilled food and the cold slowly makes its way deeper inside.
Cooling process directly within chilled goods
More and more bakeries are putting this effect to use to accelerate the cooling of their oven-fresh baked goods. What would otherwise take up to one and a half hours is achieved in a matter of minutes in a vacuum chamber. The baked goods are immediately transported to the vacuum chamber after the baking process. Once the door is closed, the pressure there is reduced to 30 to 50 mbar. The bread and pieces of cake usually reach the desired temperature of approximately 86 degrees in under three minutes. Afterwards they can be removed and almost immediately eaten or processed further. Vacuum also helps when preparing frozen foods: compared with shock frosting, only a fraction of the energy is required.