Vacuum cooler & Hydro-vacuum cooler brief introduce
Vacuum cooling involves reducing pressure inside a air-tight chamber. Water inside the vegetables turns to vapor, absorbing heat energy. Vacuum cooling works best for products that lose water easily, such as lettuce and baby leaf crops.
Hydro-vacuum coolers add a misting system to avoid moisture loss from the product. In the same time, hydro cooling can help cool down more quickly, and make some compact vegetables suitable for vacuum cooling process.
Vacuum cooling is a fast and energy efficient fresh-keeping method.
What is vacuum cooling? (In detail)
Vacuum cooling removes heat from vegetables by boiling off some of the water they contain.
Produce is loaded into a sealed strong vacuum chamber and the air is pumped out. This reduces the pressure from normal air to a virtual vacuum (<1KPa). Under these conditions, water boils at <7°C.
As water in the vegetables changes from liquid into gas it absorbs heat energy from the product, cooling it. This vapor is removed by drawing it past refrigeration coils, which condenses it back into liquid water.
For vacuum cooling to cool vegetables quickly, they must be able to lose moisture easily. For this reason vacuum cooling is very well suited to leafy products, such as lettuces, Asian greens and fresh-cut flowers. Products such as broccoli, celery and sweet corn can also be cooled effectively by this method. Vacuum cooling is not suitable for products with waxy skins, or low surface / volume rate, e.g. carrots, potatoes, tomatoes or zucchini.
For every 5°C reduction in temperature, approximately 1% of the produce weight needs to be turned into water vapor. However, modern hydro-vacuum coolers address this issue by spraying water over the produce during the vacuum process. This can reduce moisture loss to negligible levels.
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