Milk - a valuable food product.No wonder our ancestors called home cow "nurse."Thanks to its unique properties, it is a source of many nutrients and as a basis for the production of a large group of dairy and dairy products.Such production is possible because of the tendency to drink fermentation.To understand why the milk sours, let's see what it consists of.
What substances are contained in milk
milk intended for feeding young mammals.It contains a full range of nutrients necessary for the growth and development of infants.Digestibility of nutrients is very high and close to 95%.
And the milk of animals of different species differs greatly in caloric content and a quantitative biological substances.Let us dwell on cow's milk.It contains the following substances:
- Water - 87.5%.
- Fat - 3.5%.
- proteins - casein, albumin, globulin - 3.3%.
- milk sugar - lactose - 4.7%.
- macro- and micronutrients (mineral part) - 1%.
- Vitamins.
- enzymes.
- antibodies that protect infants from infectious diseases.
milk also has a certain amount of bacteria that belong to the normal microflora.They are the answer to the question "why sour milk?".Biology of microbes and consequently, the type of fermentation caused by them differ.
bacteria that cause the desired fermentation
"useful" fermenting milk involved lactic acid, propionic acid bacteria, kefir grains and dairy yeast.
lactic acid bacteria contained in the milk in vivo and are the main "culprits" of why the sour milk.Biology bacteria based on the processing of the lactose into lactic acid.As a result, increases the acidity of the beverage, and the protein casein minimized.Some species of lactic acid bacteria introduced into milk specifically for yogurt, cottage cheese, sour milk cheese, sour cream and acidophilus.This group includes: acidophilic, Bulgarian cheese, and lactic acid bacillus;lactic streptococci.
propionic acid bacteria introduced into milk in cheese production.As a result of the processing of milk sugar formed propionic and acetic acid and carbon dioxide is released.
Together with lactic acid fermentation of milk can flow and alcoholic fermentation.It called it the specific yeast and used in the production of yogurt.
For curdled whole milk is enough to leave in a warm place for 1-2 days.But for the manufacture of other products need to introduce microorganisms into the prepared substrate.This explains why the sour milk with a particular result.
tasteless yogurt
addition to the desired fermentation, some microorganisms produce butyric acid fermentation.That's why the milk turned sour - bitter.Spore-butyric acid bacteria convert lactose into carbon dioxide, butyric acid and hydrogen.As a result, the milk becomes bitter taste and unpleasant smell.Such fermentation occurs mainly in a sterilized and pasteurized milk and in the cheeses.The fact that microbes transferred butyric boiling temperature for a long time (30 minutes) and remain only inhabitants capable skvasit product.
Another reason why milk gets sour and unpleasant taste may be putrid bacteria developing in the fresh milk in the event of contamination and violation of storage conditions.Putrefactive bacteria exert their effect on the product at a temperature below 10 ° C, viable lactic acid at + 10 ° C - + 20 ° C.In contrast to the lactic acid, putrefactive microbes are killed by pasteurization, so the milk out of the package often "become rotten," and not skvashivaetsya.In this case, the microorganisms break down proteins and fat of milk, which leads to products with a characteristic decay or rotten rancid odor.
Why milk sours quickly
speed ripening of milk depends on several factors.
- The optimum temperature for the development of lactic acid bacteria is from 30 ° C to + 40 ° C.At this temperature, the milk turns sour very quickly.So keep in the refrigerator at 4 ° C.
- milk bought in the shop, quickly turns sour, even when stored in the refrigerator due to violation of production technology.These may include: failure to comply with sanitary regime at the farm during milking and transportation, failure in the sterilization process of the product, violation of the integrity of the packaging, poor quality packaging materials and so on.
should be noted that for the souring fresh milk - a natural process at room temperature, it starts after about 12-24 hours after milking a cow.Mixed milk sours quickly.To prolong the shelf life using such technological methods like pasteurization and sterilization.They are based on the heat treatment of the product, but different exposure regime.
Pasteurization Pasteurization of milk carried out in several ways:
- kept for 30 minutes at 65 ° C.
- at + 75 ° C for 15 to 40 seconds.
- temperature of 85 ° C, the processing time of 8-10 seconds.
Such milk retains a significant portion of vitamins and enzymes, and the majority of the bacteria are killed."The Story" are only heat-resistant microbes.This explains why the milk long sours.Pasteurized milk is stored in a refrigerator for 2 weeks.Also such a product is used for making various microorganisms and produce directed fermentation.
the best way to preserve the maximum of useful substances - ultra-pasteurization.With this technique the milk is exposed to a high temperature (+ 135 ° C) for 3-4 seconds.The product is then cooled to + 4 ° C and packaged in sterile packaging.Unlike conventional pasteurisation resistant spore form (including putrefactive bacteria) die.UHT milk can be stored in refrigerator for up to two months.
Sterilization Sterilization kills all microorganisms.Such sterile milk, packed in aseptic packaging, it has a shelf life up to 12 months.Everybody knows why not sour homemade milk after boiling - because the bacteria are killed.But at home not possible to conduct high-temperature treatment and to provide a free working area of bacteria and aseptic packaging.But in industrial conditions milk is sterilized at a temperature of 120 - 150 ° C for 20-30 minutes.Such a product has a lower value, because the majority of vitamins and enzymes destroyed.Also because it is impossible to prepare a lactic acid derivatives.
not sour milk from cows home?
Another reason why not sour cow's milk, may be a violation of metabolism Cows.Improper ratio in the feed sugar and protein, with protein overfeeding occurs condition called "ketosis."Ketone milk is very harmful to the human body, almost skvashivaetsya and of the separated cream turns sour with a bitter aftertaste.
Products fermenting milk
Dairy products are known since ancient times.Every culture has its own ways of preparing this wonderful and wholesome food.They differ mainly in the initial composition of milk and introduced sourdough.
- yogurt is easy to prepare at home.To do this, add the warm boiled milk ferment - a spoonful of yogurt or sour cream.Soaking in a warm place for about a day.Kefir - a Ukrainian of warm milk yogurt.
- acidophilus is recommended for people with diseases of the intestine.The product is perfectly restores the microflora of the gastrointestinal tract.
- often added to yogurt, fruit and berry fillings.
- Kefir can be of different varieties.Kefir fungi, introduced in the original product, cause lactic and alcoholic fermentation.The alcohol content of the beverage ranges from 0.2% to 0.6%, depending on the duration of ripening.Prepare the yogurt can be at home, but for that you need to get the culture of the fungus.In ancient times, kefir is so prized that leaven vigilantly guarded from prying eyes and passed from mother to daughter as a dowry.
- Kumiss prepared the peoples of Central Asia from the mare's or camel's milk.It has curative properties in diseases of the stomach and intestines, tuberculosis.
- cheese, cottage cheese, butter kisloslivochnoe also prepared with a variety of starters.
Store milk and milk products in a clean sealed container, observing the temperature and time specified on the packaging by the manufacturer.Follow the recommendations, and the question "why quickly sour milk?" Does not arise.If there is no clear guidance on the storage mode, guided by a temperature of + 4 ° C - it is suitable for almost all dairy products.Remember that dairy foods requires careful attention and spoiled food can cause serious poisoning.
