What is Vacuum Cooling?

The process of vacuum cooling for fruits and vegetables is one of the most rapid and efficient compared to traditional atmospheric or ambient cooling methods. At the same time, vacuum cooling is relatively a new technology that reduces the difference between the ambient atmospheric pressure and water vapor pressure in the product.

With the help of the pump, the vacuum cooling system eliminates all the dry and humid air from the surroundings to develop a vacuum.

With this, the vaporization of free moisture accelerates from the products.

Why is vacuum cooling important?

●       To prevent wastage and keep the produced vegetables and fruits fresh, cooling is considered an important mechanism. Reducing the temperature of the fresh fruits and vegetables increases their shelf life, helps maintain the freshness and reduces the growth of bacteria that can spoil the vegetables and fruits.

●       The traditional cooling method either used water or air to eliminate the heat from the freshly produced vegetables and fruits through conduction and convection.

●       This method has been prevailing for decades now, but it has several drawbacks. They took hours to cool a pallet of vegetables by using the forced air circulation of water jets. And during this time, the bacteria starts developing and multiplying, and the cooling water can become contaminated with such harmful bacterias.

Whereas vacuum cooling has a principle of evaporation, where the water starts evaporating from the vegetables and fruits and the energy is removed and finally, the temperature drops.

The evaporation process begins as soon as the pressure of the chamber falls enough for water to boil, and the desired temperature is set by controlling the pressure in the vacuum chamber.

Advantages of vacuum cooling:

●       The process of vacuum cooling is as fast in comparison to the traditional cooling methods. For example, a palate of freshly produced fruits and vegetables takes only a few minutes to cool down with this process.

●       It is an efficient process as it only requires a quarter of the energy of the forced-air cooling method.

●       As the evaporation takes place on all the surfaces simultaneously, the spatial distribution of the cooling is uniform.

●       Provides vacuum cooling for vegetables a longer shelf-life.

●       Another important benefit is that it offers safety because air flow is entirely in one direction, from inside to outside. Therefore there is no chance of contaminated air. The speed of cooling also offers safety as there are likely to be fewer chances of bacterial development.

Conclusion

The quality of the products keeps on deteriorating upon harvesting and continues to keep

on getting worse after that. In the case of vegetables, quality results from the microbiological and physiological activity in the harvested product. The deterioration that takes place in the fresh produce happens due to time and temperature. In simple terms, we can say that the faster the harvested products are cooled, the better the quality and the longer shelf life it will have. To achieve this, the process of vacuum cooling is required as vacuum cooling is considered one of the best postharvest cooling methods. It helps to maintain the temperature of the product quickly and uniformly, making the products more efficient. 

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Not all foods are suitable for vacuum cooling. Because the process is based on evaporation, the product must contain sufficient water for cooling to be effective. In addition, leafy vegetables such as lettuce, which have a large surface area, can be cooled more efficiently than solid ones such as tomatoes. But neither of these requirements is as restrictive as you might expect. 

Many foods that feel relatively dry in the mouth, such as bread, nevertheless contain enough water to be vacuum cooled. And because vacuum cooling typically only removes a few per cent of the product’s water content, the loss of mass is less than you would get with forced-air cooling – minimizing the loss of revenue on foods sold by weight.

Advantages and challenges of vacuum cooling

Advantages

Challenges

●       Shorter cooling times (cooling from 212°F/100°C to 86°F/30°C can be achieved in only 3 to 6 min) ●       Lower risk of post-bake mold contamination ●       Product can be cooled in a 20 m2 equipment instead of a 250 m2 cooling tower ●       Superior crust appearance and better symmetry as product shrinkage is greatly reduced ●       Product remains crusty to reduce chance of collapse during slicing

●       Greater weight loss since cooling is carried out only through moisture evaporation ●       Higher initial investment costs ●       Scaling weight at divider and % absorption must be adjusted according to finished product moisture ●       Somewhat lower yield per dough batch since scaling weight is usually increased to meet declared product weight ●       Higher energy consumption at bakery ●       Accelerated staling may occur with higher cooling loss