The products, which are put in hang

The products, which are put in hanging meshed boxes, are transported along a cool bath. In the method of Fig. 9-17b the product is immersed in a
bath, while water circulates through the product. In the method of Fig. 9-17 c,
the relative motion between the product and the cool water is achieved by the
rotation of a drum, which is partially immersed in cool water. Inside of the perforated
drum, there are helical baffles, forwarding the product during the drum
rotation. At the same time, the product is lifted by the rotating drum up a certain
height, and it falls back to the water (tumbling). This type of equipment is often
used for leafy vegetables (e.g., spinach). The method can be continuous, or
batch (if there are no screw baffles in the drum). This kind of equipment is also
preferably used in chilling of poultry because, in comparison to air cooling, less
weight is lost. For poultry chilling, one to three drums may be used (two or
three drums, in series), in which poultry rotates in a counterflowing ice-water
mixture, for 20--30 min. The consumption of ice is 0.6--0.9 kglkg poultry. Such
equipment requires a surface area of 18-20 m2• The capacity of such drums is
up to 6000 birdslh (de Fremery et aI., 1977). Poultry, immersed in water for
washing, precooling, and chilling, gains a significant amount of water, especially
in its skin and in its fatty tissue (about 8%). USDA-established tolerances
and an EU legislation (Regulation 2967/76) restrict the maximum water gain
(James and Bailey, 1990a).
The equipment in Fig. 9-17 d,e is used for cooling meat. The method is called
evaporative air chilling or spray chilling. The water activity of the surface of the
product is maintained very high by wetting it with water sprayed through nozzles
on both sides of the product. At the same time, cool air is blown on the food. In
poultry, the carcasses can be sprayed with cold water (about 5°C), seven to eight
times in short burst intervals for about 1 h. This, together with cool air (T < 8°C),
reduces the temperature of the carcass from about 30°C down to 4°C. The quantity
of water used is 0.5 Llcarcass (Mulder et aI., 1990). This method was also
tried in chilling pork and beef carcasses. The chilling of beef lasted more than 8 h
(James and Bailey, 1990a). Water of 2-3°C was sprayed repeatedly from 11 nozzles.
Each time, 1 Llnozzle was sprayed for 30 seconds (James and Bailey,
1990b). In the case of fruits (Fig. 9-16e), up to 3 stacked pallet boxes move on
rails. through a tunnel, in which nozzles spray cold water, containing a protective
fungicide. The capacity of a unit of 12 X 2 X 4 m, cooling apples with water of
about 7°C, can be 200--220 pallet boxeslh. The required energy for the pumping
system is 8-12 kW. The equipment of Fig. 9-16f can be used as part of immediate
further processing of products that are sensitive to mechanical stresses. In comparison
to the immersion method, advantages of spray chilling are the reduced
water consumption and water product absorption. Disadvantages are the inducement
of microbial growth, due to high water concentration on the surface of the
carcasses, and the relatively higher total energy requirement. The equipment in
Fig. 9-17h is similar to that in Fig. 9-17 g. They differ in the additional spraying,
occurring during the rotation. These machines are combination equipment, in
which the product is immersed in cool water, and sprayed. They are mainly used
for fruits and vegetables. Water is cooled in a heat exchanger and recirculated.