The final cooling temperature plays an important role in the time to cool. The first stage of cooling, down to around 5⁰C, is always very fast (providing the vacuum cooler is fast enough), but cooling down to around freezing temperatures requires much more time, as the graph shows.

Other advantages of vacuum cooling methods include that paper and plastic packaging materials in the boxes do not affect the efficiency of cooling, free water is removed, boxes can be packed tightly and stacked in any manner in the pre-cooler.

Vacuum Cooling Technology Explained

Vacuum works with pressure. There is a relation between the pressure level and the boiling point of water. The lower the pressure, the lower the boiling point of water. When introducing a product recently harvested into the vacuum room, vacuum pumps start evacuating much of the air lowering the pressure inside the room. When the pressure level reaches the product’s temperature, a fraction (0,8 – 2%) of the moisture inside the product is being forced to evaporate. This evaporation process extracts energy (=heat) from the product, cooling the in- and outside of the product evenly, from the core. Because of the created vacuum, not only the outside is cooled down, but the product’s core as well, as cooling takes place from inside the product.

Vapor flow at final pressure is huge and would require very big vacuum pumps. Using a condenser to trap the vapor flow is more economical!  vacuum coolers operate with very efficient condensers using glycol/water coolant (-5 to -0°C) for a fast cooling. The hot vapor passes through the heat exchanger through which it is re-condensed and drained out of the room. When the cycle is finished, vacuum pumps pump air into the room and the door can be opened again.