Churning

The cream (emulsion of fat in water) is subjected to buttering, that is to say to a set of operations that transform it into butter (emulsion of water in fat). As mentioned, the cream must first be pasteurized at 90-95 ° C for 15-20 seconds; for creams of poor quality, higher temperatures are used (105-110 ° C). those used to pasteurize the milk (65-85 degrees), necessary first of all for the higher density of the cream, which hinders the achievement of the thermal equilibrium in all its parts, secondly for the abundant lipid fraction, which acts as an insulator thermal protecting microorganisms from heat, and finally because cream has a higher microbial load than milk.

The preventive standardization processes - necessary to adjust the lipid content of the cream - of neutralization - in which the acidity is corrected to avoid problems during pasteurization - and deodorization are also very important.

After all these treatments have been carried out, the cream is quickly cooled; in a short time it goes from 90-95 ° C, reached during pasteurization, to a temperature of 6-7 ° C, at which the cream is left for about two hours; this step is called crystallization, because the sudden decrease in temperature causes the triglycerides to solidify. This step must take place as quickly as possible, because only in this way abundant and above all small crystals are formed; if, on the other hand, the cooling process is slow, few large crystals are formed (with a decrease in the spreadability of the butter).

At the end of the crystallization process, the cream still appears as an "oil-in-water emulsion", since the phase inversion has not yet occurred; if it is sweet, it is also devoid of aroma, which is conferred on it only by the subsequent inoculation of selected bacterial cultures (acidifying bacteria: Streptococcus lactis And cremoris; flavoring bacteria: S. diacetalactis And Betacoccus citrovorus). This phase is superfluous for butters produced from sour cream, which unlike that obtained by centrifugation (sweet cream) already possesses the organoleptic characteristics typical of butter (the main compound that gives the product its typical aroma is diacetyl, a which are associated with substances such as acetylmethylcarbinol, 2-3 butanediol and acetoin).

In the subsequent maturation phase the bacteria are left with all the time necessary to carry out the aforementioned transformations; this phase takes place in closed steel tanks (tanks), containing a blade inside them, which keeps the mass in motion, and covered with a jacket in which water circulates; in this way it is possible to keep the temperature of the cream relatively constant (16-21 ° C) for 10 hours or a little less.

When the cream reaches acidity values close to pH 5, the maturation process is interrupted by passing cold water through the jacket of the tanks. It is necessary to reach slightly acidic pH values to allow the denaturation of the lipoprotein membrane (which surrounds the fat globules) and to facilitate the subsequent steps.

When maturation is complete, churning is carried out, which consists in the rapid whipping of the milk cream (about 60 rpm) in special machines called churns; this determines the collision between the fat globules and the coalescence of the lipidic material contained in them, whose escape is facilitated by the denaturation of the membrane that surrounds them (thanks to the acid pH acquired in the previous phase of maturation, to the mechanical action of whipping and at the low temperature at which the churning is carried out). The triglycerides escaping from the globules thicken into a solid mass that also envelops intact globules (coalescence) giving rise to lumps of butter the size of a grain of rice or corn that separate from the buttermilk.

The whole operation, carried out at 8-13 ° C, takes about 30 minutes. During this phase there is the inversion of the emulsion, as fat globules are formed (small lipid clusters similar in size to grains of rice or corn, which collectively take the name of raw butter) from which the buttermilk is expelled. The latter is removed by frequent washing with cold water; this operation is important - among other things - to increase the shelf life of the butter, as buttermilk is an excellent breeding ground for bacteria.

At the end of this phase the product appears as a non-compact mass, formed by many small grains; it must therefore be kneaded, formed into loaves and sent for packaging.

The one just illustrated is the traditional process for the preparation of butter and is a discontinuous method. In addition to it, there is an alternative production technique, called NIZO; the steps are the same, but the moment in which the inoculation of bacterial cultures is carried out changes; while in the traditional process it is performed before churning, in the NIZO one it is done after the conversion of the sweet cream into raw butter. the two methods have the same nutritional and organoleptic characteristics; however, while in the first case we obtain an acid buttermilk, in the second we obtain a sweet buttermilk, therefore without aromas; the NIZO process also allows better control of fermentation.

The choice of one process over the other depends on the uses to which the buttermilk is destined; it is clear that when the cream is obtained from whey, therefore from a "waste" product from the manufacture of cheese, the buttermilk will now be free. of nutritional substances; on the other hand, if you start from milk you get a whey richer in nutritional substances, such as mineral salts and proteins, therefore suitable for the production of other milk derivatives. type of derivative to be obtained (depending on the product it may be useful to have a more or less aromatic whey).

In addition to discontinuous churning, there is also a continuous type of churning, which is carried out to produce butter on a large scale. The processes and phases are always the same, with the only difference that all the steps take place within the same plant.

The processes most used in butter-producing EU countries are based on the FRITZ method, which follows the same principles as batch buttermaking. The butter obtained with the Fritz method, from the chemical and organoleptic point of view, is indistinguishable from that of churn, but the yield is slightly lower and the percentage of globular fat is also lower.