Technology of kefir

Kefir is a dietary acidic dairy product of Caucasian origin. From a chemical point of view, kefir is the result, mainly, of a double fermentation: lactic fermentation and alcoholic fermentation as a result of the development of lactic bacteria (streptococci and lactobacilli), yeasts and acetic bacteria in milk, through the kefir granules .

Kefir granule is an agglomeration of cauliflower-like casein that contains in it and on its surface the microorganisms that participate in fermentation. The kefir granule has a diameter of about 1 cm, but as soon as they have been recovered from milk, its diameter is larger (2 - 5 cm), being white, with a spongy, elastic structure. The surface of the granule contains almost only lactococci and streptococci, while inside the granule lactobacilli and yeasts predominate.

The manufacture of kefir can be done by two processes:

the traditional (classical) process;

the valve process, which can be: valve process with kefir granules and valve process with starter cultures;

Milk reception, filtration and cleaning

Whole cow's milk intended for the production of kefir is first received, filtered and cleaned of the impurities contained, after which it is processed.

Normalization of milk

In order to obtain kefir with a content of 3.3% fat, whole milk is normalized by adding skimmed milk, an operation that is performed in the valve in which the pasteurization, sowing and fermentation of milk is to be done. Regarding the expected fat content of normalized milk, 3.3%, it is stated that it is set by the standard, but the product can also be manufactured with a lower fat content, even whole milk, if provided in Firm Standard approved by manufacturing license.

Pasteurization and cooling of milk

The pasteurization operation is performed in double-walled or spiral-channel valves and consists of heating the milk to a temperature of 85 - 87 ° C and keeping it for about 20 minutes. In sections equipped with plate pasteurization plants, milk heating can also be performed in these plants combined with heating in valves. After pasteurization and maintaining the expected temperature, the milk is cooled to the sowing temperature, which differs depending on the season, being 18 - 20 ° C in summer and 22 - 24 ° C in winter. For this purpose, mains water is introduced between the double walls or in the spiral channels of the valve, and the milk is stirred during cooling.

Sowing and fermenting milk

To ferment milk and obtain the product with specific properties, the milk is sown with a lyophilized culture consisting of strains of Lactococcus lactis, Lactococcus cremoris, Leuconostoc cremoris, Lactobacillus brevis and Saccharomyces cerevisiae.

In order to distribute the lyophilized culture or added mayonnaise as evenly as possible, the milk in the tub is stirred for 3-4 hours, during which time an increase in acidity of up to 35-40 ° T occurs, after which it is left to rest. , for further fermentation and coagulation. Due to the favorable conditions that are ensured, the microorganisms from the lyophilized cultures or the added mayonnaise, produce in milk a double fermentative process, respectively the lactic and alcoholic fermentation. Thus, the lactic acid bacteria contained in the first phase produce lactic fermentation, which causes an increase in acidity and coagulation of milk. Also, in this phase, specific flavoring substances are produced and a process of partial decomposition of proteins takes place, resulting in a higher proportion of soluble compounds. In the next phase, the yeasts present in crops that ferment lactose act, resulting in reduced amounts of alcohol and gases. Depending on the temperature and the duration of the fermentation processes that take place, the ratio between lactic and alcoholic fermentation can be modified, so that the product to be obtained has more characteristics of acidic dairy product or low-alcohol soda drink. . From this point of view, the manufactured kefir can fall into three types:

weak one-day kefir, having an acidity of not more than 90 ° T and not more than 0,2% alcohol;

the medium two-day kefir, having an acidity of not more than 105 ° T and not more than 0,5% alcohol;

hard kefir, three days old, having an acidity of not more than 120 ° T and not more than 0,8% alcohol;

Among these types of kefir, the product with the best dietary and nutritional properties is the weak kefir, with a short fermentation time (one day) and having a lower alcohol and gas content.

The fermentation of milk to obtain kefir is carried out as follows:

Fermentation I (lactic) - of milk is carried out at a temperature of 20 - 24 ° C for 8 - 12 hours, being considered completed when a well-formed curd is obtained, with an acidity of 80 - 90 ° T. When these conditions are met, the lactic fermentation process is interrupted by cooling the coagulated milk to a temperature of 12-14 ° C. For this purpose, cooled water is introduced between the double walls of the valve, and the curd is stirred throughout the cooling. Interruption of the fermentation process of the milk before the acidity reaches 80 - 90 ° T gives the product too fluid a consistency, and if this operation is performed later, when the acidity reaches 90 - 100 ° T, a too dense curd results and remove whey.

Fermentation II (alcoholic) - is made at a temperature of 12 - 14 ° C and lasts 6 - 12 hours, during which time the acidity of the curd should not increase by more than 5 ° T, instead the conditions are favorable for the activity of yeast from cultures that produce alcoholic fermentation. Periodic agitation of the curd is recommended during the second fermentation. From the above it appears that the fermentation of milk is one of the most important operations of the technological process of making kefir and that the quality and specific properties of the product obtained depend on the way in which it is made.

Product packaging

After the fermentation process is completed, the curd in the valve is shaken, thereby aiming to obtain the product with a uniform consistency throughout the mass, thus being prepared for packaging. In order to prevent the clumping of the curd from advancing too much, it is recommended that the food of the machines be made by free fall, avoiding the use of centrifugal pumps. For this purpose, the fermentation valve shall be placed on a platform at a sufficiently large level difference from the packing machine.

The packaging of kefir can be done in plastic cups, closed by heat-sealing with aluminum foil and closed bottles (PETs) with threaded lid. The packaging operation can be performed with semi-automatic or automatic machines. The labeling and marking of packaging shall be carried out in accordance with the specifications laid down in the Methodological Rules on food labeling and other legislation, which shall be printed directly on the packaging or on the label applied, except for the expiry date which shall be printed on the packaging.

Product storage

The manufactured kefir is stored in clean, disinfected refrigerated spaces, without foreign odors, at a temperature of 2 - 8 ° C, where it is stored at least 12 hours before delivery, in order to complete the maturation process. It is recommended that in order to obtain the best possible quality, the product be kept in the same conditions for up to 24 hours, after which it will be delivered. In addition to these conditions, the legal provisions in force will also be observed when storing the product.

The characteristics of the finished product

appearance and consistency - fine, homogeneous curd, creamy consistency (similar to sweet cream), but effervescent;

color - white-yellow, uniform;

sour taste - pleasant, slightly pungent and refreshing;

smell - of yeast, of alcohol;