Processing milk or it into butter, or for cream or lean cheeses, it requires the previous separation of fat from it in the form of cream.
Fat is separated from the milk:
1. spontaneously under the influence of gravity,
2. using centrifugal force, that is, using a centrifuge.
The release of cream under the influence of gravity is called a pod. One cannot do without it in cheese dairies making cheese from skim or partially harvested milk, primarily for this reason, that the centrifuged milk compared to the milk collected from the stand, fat content excluded, behaves worse during conversion. The impact of the shocks, infection on contact with the ducts, flat, difficult choice, etc.. are not irrelevant.
In the milk left undisturbed, fat globules rise up after some time under the influence of gravity and form a layer of cream. Not all fat passes into it. The degree of degreasing is at various standstill methods 75 do 85%, that is, it remains 0,5 do 0,8% fat in skim milk.
Standby methods. A common feature of almost all stackable methods except the Stuartz method is principle, to pour the milk into shallow dishes as soon as possible after milking and place it in a clean, airy place at 12 do 15°C na 12 do 24 hours. The old standstill methods have completely lost their importance in buttermaking, while in cheese making, some of them remain necessary to this day, and these are all we care about.
In more recent times, rude is used for two purposes:
1. to collect cream (stand),
2. to get the milk to a certain state of anger (standoff).
The Swiss method of serving is used to collect cream and obtain bad milk. Midday and evening milk are placed in shallow capacity bowls 8 do 10 1 on the shelves in the cold store. This cooler is cemented, often equipped with tanks, through which cold mountain water flows, it is usually on the north side, shaded and provided with louvered windows to the openings, so that the air current passes over the milk bowls. In winter, the temperature in the cold store should be kept below 15 ° C.
In the morning, the cream is collected with a perforated trowel, usually just for that, to melt it separately and mix it thoroughly with the milk in the cauldron again. In this case, it is only about proper milk storage and making it sufficiently angry. On the other hand, cream cannot be returned to the milk, when lean cheeses are made, or when it is intended to reduce the fat content of the processed milk, e.g.. With 3,7 on 3,2%, what else is enough, to obtain a cheese with a fat content in dry matter 45%.
Stand bowls are pressed from seamless sheet metal and thickly whitened in a bath. Wooden bowls are also used, usually fir. They are preserved and sealed in this way.
The bowls are scrubbed in hot short circuit, then rinsed with hot water and dried in the shade. This treatment is repeated from time to time, until they are covered with a thin layer of hard enamel, the so-called. milk stone. Such bowls are believed to have a more beneficial effect on contamination of milk than tin plates, what is possible, because they can contain beneficial bacteria in their pores.
The Stuartz method consists in storing milk in tall, flattened vessels. This method produces worse results than the previous method, possibly for this reason, that the high layer milk retains its original high temperature for too long.
Milk stored in cylindrical racks behaves in a similar way, and the bigger they are, so much the worse.
As for the degree of degreasing, the Siuartz method is sharper than the basin method with the use of bowls.
Frisian way. Big cheese factories in Friesland, avoiding the admixture of milk centrifuged in the production of lean cheeses, introduced at home in order to save dishes, place and time, a new way of standing up similar to the Siuartz method. Tanks with a capacity are used 2000 do 3000 1 milk, with bottoms inclined towards the drain cock. Some tanks have, apart from the lower one, an additional tap below the level of the overlying cream layer. The depth of the tank should not exceed 45 do 50 cm. Where there is no refrigeration unit, the milk is cooled with water 12 to 13 ° C and stand them by 10 hours. Of course, the shelf life of insecure milk may suffer at this temperature. So the described method was changed there, where are the refrigeration equipment, by doing so.
The supplied milk is heated to temperature 35 do 40°C. immediately cools to + 6° C and at this temperature it is kept in tanks for 10 hours. The cream is drained either with the top tap, or the lower one, having first drained the stale milk. In both cases, the sediment is retained on the strainer. The milk is led directly to the cheese tub through the gutter.
The latter method gives a sharper result than the first, for the residual fat is 0,6 do 0,8% depending on the season and lactation period.
The effect of heating and subsequent cooling on increased fat release has not yet been adequately explained. Contrary to the known laws of physics, fat globules concentrate rapidly and rise to the surface. It is not known yet, how does the heat that is released during the concentration of fat work here?.
The Normandy method used in some parts of northern France during the winter season is like this, that the milk is first heated to 50 – 55°C. Then they are poured into shallow bowls and placed in a cool and airy room. At this starting temperature, the release of cream is accelerated, and when it drops below 35 ° C, promotes the growth of lactic acid bacteria. This temperature does not hold, because the shallow layers of milk assume the ambient temperature, i.e.. around 12 ° C, which again has a positive effect on the selection of the right lactic acid bacteria. This method is very old, empirical, today finds scientific justification.
Separating cream by force from the middle. Various systems are used for this purpose. When choosing a centrifuge for cheese-making purposes, we give priority to these, which:
1. they draw in as little air as possible and create as little foam as possible,
2. they do not have too many rotor revolutions,
3. they do not clog easily; this is important in the centrifugation of whey containing spray cheesecake, whose sieve does not stop, unless special additional rotors or a separate centrifuge designed for this purpose are used.
Too long and strong spinning of the milk, drawing air and foaming reduces the value of the cheese spin milk. The milk froth must be carefully collected, because it is an obstacle in the clot.
One must also point out, that the milk is cleaned with at least a separate centrifuge, secretes cream slightly faster than strained. It was also noticed, that the agglomerates of bacteria break up during the spin cycle, to which is attributed some beneficial effect on the even distribution of the eyes in the cheese.
It's worth pointing out, that the milk separator retains approx 80 do 90% impurities not dissolved in milk, while wire strainers only 50%.