Vacuum conditioning utilises the fact that the boiling temperature of water depends on the ambient pressure. The pressure in the vacuum conditioning cell is lowered during vacuum cooling. By reducing the pressure, some of the water present in the baked goods evaporates and extracts heat from the hot baked goods, as energy is required to change the aggregate state from liquid to gaseous. This energy is also known as the enthalpy of vaporisation. The baked goods cool uniformly on the inside and the outside simultaneously.
Pressures of 50 – 300 mbar are used when cooling and stabilising baked goods. At a pressure of 50 mbar, the boiling point of water is around 33° C, at a pressure of 300 mbar it is around 69° C.
A pressure of over 300 mbar has hardly any significant effect on most types of baked goods. At a pressure of less than 50 mbar, the risk of baking faults increases (dry crumb, crumb cracks, hard and brittle baked goods). The required pressure and the duration of the cooling process in the vacuum chamber depend on the size and structure of the baked goods and the desired baked goods properties.