Farm cooling equipment
Spray or immersion coolers are commonly used on farms, which deliver
milk to the dairy in cans. In the spray cooler, circulating chilled water is
sprayed on the outsides of the cans to keep the milk cool. The immersion
cooler consists of a coil, which is lowered into the can. Chilled water is
circulated through the coil to keep the milk at the required temperature
(Figure 1.13 to 1.15).
Where milking machines are used, the milk is commonly collected in
special milk tanks at the farm (Figure 1.16). A wide range of milk tanks of
various sizes are available with built-in cooling equipment designed to
guarantee cooling to a specified temperature within a specified time. These
tanks are often in most cases equipped with equipment for automatic
cleaning to ensure uniform high standard of hygiene.
On large farms, and in collecting centres where large volumes of milk
(more than 5 000 litres) must be chilled quickly from 37 to 4 °C, the cooling
equipment of the bulk tanks may be inadequate. In these cases the tank is
mainly used to maintain the required storage temperature; a major part of
the cooling is carried out by means of a heat exchanger in line in the
delivery pipeline (Figure 1.17).
Frequency of delivery to the dairy
In former times, milk was delivered to the dairy twice a day, morning and
evening. In those days the dairy was close to the farm. But as dairies
became larger and fewer, their areas of collection increased and the
average distance from farm to processing increased. This meant longer
intervals between collections.
Collection on alternate days is common practice today in most of the
large dairy countries with modern milk production. Collection every three or
even four days is not entirely unknown.
Milk should preferably be handled in a closed system, to minimise the
risk of contamination. It must be cooled to 4 °C as soon as it is produced