Vacuum cooling is an ideal way to cool specific fresh produce, such as leafy vegetables and flowers, quickly. A vacuum-cooler can cool produces down from field temperature to about 2°C in 15 minutes. Not only does this guarantee the quality, but it also allows for quick logistic processing and large quantities. A vacuum-cooler is not suited for larger produces such as beans or sugar snaps. For these types you are referred to the pre-cool room.
The technology of vacuum-cooling is based on two principles: water boils/evaporates at lower temperatures if the pressure drops. And when water evaporates the surface cools down dramatically. You might know that boiling a pot of tea takes less time on top of the Mont Blanc than at sea level. This is due to the lower air pressure at the top of a high mountain. For the second principle, please remind yourself of the times you went into the sea, only to find out that the water was so cold. That must have been an unpleasant experience, but as long as your were submerged, it was still okay. Once out of the water, you regretted it: the wind evaporates the water on your skin and that is why you cool down: towels, quickly!
A vacuum cooler consists of a large barrel, the kettle, often a container. In order to reach negative pressure, vacuum pumps that suck air out of the kettle have been installed. At some point during pumping, the water on or just below the surface of the fresh product will ‘suddenly’ evaporate: we have reached the pressure that makes the water boil at that respective temperature. This moment is called the flash point.
To dispose the water, a cooler has been placed inside the kettle. It is here that the water damp can condensate. The water will then be drained, as to properly boil it and avoid condensation on the fresh goods.
The difficulty of the technology behind vacuum cooling is the capacity one suddenly needs at the flash point, creating the precise negative pressure and selecting the right kettle. This kettle should be strong enough to withstand the negative pressure and be absolutely leak-proof. But logistics are likewise important: your wrapping should fit and easily be loaded and unloaded.