ABSTRACT
Vacuum cooling is proven to be an effective precooling
method for porous and large surface-to-mass ratio pro-
ducts. The energy required for cooling is provided by the
product itself with the evaporation of water during applica-
tion of vacuum on the product. Vacuum cooling provides a
uniform, fast, and economical cooling compared to con-
ventional cooling methods. Although it might cause water
loss from the product during cooling, vacuum cooling
found applications in the food industry to cool specific
products such as lettuce, bakery products, and some meat
products. It is also being used for prechilling of floricul-
tural products for shelf life extension. A recent review
paper discusses principles, equipment, and development
of this technology for the agri-food industry.[1]
PRINCIPLES AND EQUIPMENT
Vacuum cooling is based on the principle that the boiling
point of water changes with pressure. As the pressure
decreases, boiling point temperature also drops as illustrated
in Fig. 1. Vacuum cooling is achieved by evaporation of water
from the product at very low air pressure, and the energy
required to evaporate the water (latent heat of vaporization) is
provided by the heat available in the product itself. This
allows uniform cooling of even tightly packed produce.[2]
The quantity of heat given off by the product, indicated by
(kcal hr-1), during cooling could be expressed by[3]
¼ W C ðT2 T1Þ t
(1)
where W is the weight of the product (kg), C is the specific
heat of the product (kcal kg-1 C-1), T1 is the product’s entering temperature (C), T2 is the product’s leaving temperature (C), and t is the time of cooling (hr).
