Acid and acid-alcohol milks
Fermented milks and yoghurt are considered "SPECIAL LATTEE PREPARATIONS" (RD 1929). All the products obtained by coagulation, without serum subtraction, are included in the category due to the exclusive action of characteristic microorganisms, which must remain alive and vital until they are consumed.
Fermented milks differentiate into:
ACID MILK: yogurt, leben, gioddu ("homolactic" acid fermentation).
ACID-ALCOHOLIC MILK: Kefir, Koumis (acid and alcoholic fermentation, called "heterolactic").
The two categories of products differ on the basis of the microbial strains used; in the first case the bacteria operate a simple fermentation of lactose with the production of lactic acid (homolactic); in acid-alcohol milks, on the other hand, fermentation originates lactic acid and ethyl alcohol.
Among the acid milks, gioddu is a typical Sardinian product, a kind of yogurt made from sheep's or goat's milk; the leben is instead a traditional food of the Moslem countries facing the Mediterranean, in which the fermentation takes place inside skins obtained from the stomach of kids or lambs.
Among the acid-alcohol milks, kefir and koumis are more than anything else fermented and foaming milky drinks. Kefir is obtained from: torula yeast (alcoholic fermentation), Lactobacillus brevis, L. casei, Leuconostac mesenteroides and Saccharomyces cerevisiae, while Koumis is obtained from fermented milk with a pure Kumiss culture.
The Yogurt
Among all the fermented milks, yogurt is the most consumed food in our country; it is produced by exploiting the action of two microbial strains - the Lactobacillus bulgaricus and the Streptococcus thermophilus - in specific ratios, which can be 1/1 - and in this case you get a more acid yogurt - or 1/2, obtaining more velvety products . In fact Lactobacillus bulgaricus has a greater fermentative aptitude and as such determines a lowering of higher pH.
The raw material for the production of yoghurt is obviously milk, which can be skimmed, partially skimmed, or whole. After undergoing a heat treatment, the homolactic fermentation leads to the formation of lactic acid and a series of intermediate products (acetylmethylcarbinol, diacetyl, acetaldehyde, organic acids) which give the typical aroma of this food product. L. bulgaricus, for its part, produces viscous substances that give a velvety consistency to yogurt.
The preparation process depends on the type of yogurt you want to get. The initial phases are however somewhat identical for all the products; the preparation of the milk, in particular, provides for a standardization, therefore a normalization of its lipid content and dry residue (for a whole yogurt, for example, the lipid content must be higher than 3%; more generally the industrial product must always have the same composition even if starting from milks with different composition, then cream or cream will be added, to correct the lipid content, or an addition of milk powder to increase the quantity of proteins and sugars). The whole must naturally be homogenized and subjected to heat treatment, which is carried out in more drastic conditions with respect to milk pasteurization (either the temperature is increased or the exposure times to heat are lengthened); the heat has in fact the aim to denature proteins - facilitating the formulation of the clot - and to kill all the microorganisms present. After the thermal treatment the functional microbial strains are inoculated, which are precisely the Lactobacillus bulgaricus and the Streptococcus thermophilus .
Second part "
