Yogurt occupies a large space in the refrigerated counters of shops and supermarkets, in fact we find a great choice of different tastes and brands.
The discovery of yoghurt by consumers is recent, as its spread as a food has gone hand in hand with that of refrigerators. But the birth of yogurt was lost in antiquity, when nomadic shepherds of the Middle East discovered that the milk that suffered a particular fermentation was tasteful and can be stored for many more days than raw milk.
BUT HOW DOES YOGHURT BE PRODUCED?
Yogurt is a milk fermented by specific lactic bacteria such as Lactobacillus bulgaricus and Streptococcusthermophilus. Milk inoculated with these bacteria is brought to a temperature of 40-45°C, which is necessary for their proliferation.
When the milk begins to coagulate and take the consistency of a gel, other ingredients are added (e.g. sugar and fruit, aromas), and then it is homogenized and invested. With this process the starting milk is somewhat transformed, starting from the consistency, becoming from a liquid substance to a gel, the composition of the nutrients also changes in part.
Lactose, which is the sugar naturally present in yogurt, is fermented with the production of lactic acid responsible for the characteristic aroma. Lactic bacteria slightly enrich yoghurt with essential amino acids and B vitamins, and calcium is made more bio-available to be absorbed at the intestinal level.
These lactic bacteria, when the yogurt is fresh, are found in amounts of 10 million per gram and manage to keep alive and vital for a long time (35-45 days) if the jar is stored keeping the cold chain, after the expiration date these bacteria begin to decrease in number, then to die. It is normal for these bacteria to die, since the jar has a limited space that, at the same time, contains a limited amount of the product.
Bacteria slowly finish lactose being their food. But the product still remains edible, for a few more days.
The only precautions to be taken are to observe that the jar has not swelled, and that at the opening there are no strange colors or the presence of mold on the surface, that there is no characteristic smell a little acidic; in these cases its consumption is better avoided in order not to encounter unnecessary food poisoning.
Have a good snack!
Dr. Andrea Riva