Vacuum Cooling: How does it work?

Vacuum Cooling


What is Vacuum Cooling?

Vacuum cooling is a rapid and more efficient alternative to traditional atmospheric or ambient cooling. It is a relatively new technology based on reducing the difference between ambient atmospheric pressure and water vapor pressure in a product.

  • By using a pump, the vacuum cooling system removes dry and humid air from the cooling environment to create vacuum.
  • This accelerates the vaporization of free moisture from the product.1,2
  • High speed bakeries benefit from this technology via reducing cycle times and efficient usage of production plant floor space.

Origin

Implementing vacuum cooling in the baking industry has emerged in response to bakeries’ need for reducing the time from the ingredients scaling step through product packaging.

Most high-speed bakeries use no-time dough systems which require about 3 hours to produce bread. Under vacuum cooling conditions, bakers can reduce the time it takes to produce bread down to about 2 hours.

How it works

In this process, loaves coming out of the oven at temperatures close to 205°F (96°C) are placed or conveyed directly into a vacuum chamber. It’s sized based on processing requirements, pieces per minute produced, and floor usage. Once the product is loaded, the vacuum chamber is then sealed to prevent gas exchange.

A vacuum pump starts working by removing air from the cooling chamber, hence decreasing the air (atmospheric) pressure in the chamber. The vacuum created inside the equipment (partial or total) lowers the boiling point of water in the product. Subsequently, the moisture present in the product starts to evaporate quickly and steadily. The boiling process requires latent heat of evaporation, which is withdrawn through the product crumb. This results in a temperature drop and allows the loaf to cool down.2,3

As the cooling process continues, the vacuum pump drains the water vapor through a condenser which collects moisture and channels it to a separate location.

Vacuum cooling parameters

  • Vacuum pressure of operation
  • Cooling time
  • Product load (lb/batch or lb/min)
  • Product temperature drop
  • Condensate amount

Application

The speed by which vacuum cooling works makes it an attractive technology for less stable bakery products that may be prone to collapse as they cool. This process allows bakeries to avoid the dependence on prevailing atmospheric conditions, thus achieving consistent results and uniform cooling at all times. Equipment required for this purpose must be isolated and sealed from the surrounding area and may be operated in batch or continuous modes.

Batch-mode vacuum coolers

In some cases, vacuum coolers are designed as batch-mode systems that have to be properly connected and synchronized to the continuous up- and down-stream operations in the bread production line. When such situations occur, several adjustments must be made in order to prevent the cooling equipment from becoming a production bottleneck, such as:

  • Cycle time management (timing of cooling, holding and transfer times)
  • Labor needs in case of semi-automated product handling
  • Product holding and transfer equipment
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