Vacuum cooling systems are the preferred system for leafy greens and other products with a large surface to mass ratio. Systems can cool 3 to 20 tons in 30 minutes cycles. Sizes from 2 pallets (about 1.5 MT) to 8 pallets (6 MT) designs offer mobility, wet and dry operation, and a variety of shuttles and door configurations. The best are made with T304 stainless steel to meet stringent export sanitation standards and food safety regulations. Equipment capable of handling 24 pallets (18 MT) are in use in some regions.

The principle of Vacuum Cooling is based on the reduction in the boiling point of water at reduced pressure, a phenomenon well-known to those who live at higher elevations. At 6 millibar, or 0.6% of an atmosphere, the boiling point is lowered to 1 deg C. Precise control is required of the pressure in this region, for a drop to 5 millibar may freeze some products. While the end point can be touchy, systems can be automated for consistent and failure-safe cooling.

Vacuum cooling works by forcing a portion of the water found in the produce to evaporate at a low temperature, simply by lowering the atmospheric pressure around the produce. The energy required to evaporate the water comes from the produce itself, resulting in evaporative cooling.

As mentioned, vacuum cooling is particularly well suited to pre-cooling vegetables with a high surface to volume ratio, in particular leafy vegetables such as lettuce, endive, and spinach. Produce with high permeability to water vapour such as sweet corn and cauliflower may also be successfully vacuum cooled since the water vapour can escape rapidly as it forms.

Vacuum Cooling features

Advantages
●　Cools large volumes and weights of produce rapidly
●　Uniform temperature easily obtained
●　Optional moisture enhancement systems can reduce weight loss
●　Sanitizing agents can be incorporated in moisture enhancement systems
●　High volume users can achieve low unit costs with correctly matched equipment

Disadvantages
●　Larger sizes (over 6 tons) can present challenges in relocation
●　Initial cost can be high
●　Moisture enhancement systems cannot be used on some packaged products
●　Not suitable for dense produce

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