Equipment, devices and technical facilities:

Cream with fat content of 20-25 %; cow milk; starter culture for sour cream, reagents and apparatus for determination of titratable acidity and the mass fraction of fat in milk and cream, centrifuge tubes, consistometer, thermometers, thermostats, valve homogenizer; measuring cups, cylinders, buckets, whorls, glass beakers with a capacity of 250 ml.

The work order

Syneresis properties – 10 ml of the investigated product is placed in a measuring tube and centrifuged for 30 min, determining every 5 min the volume of the evolved serum, constructing a graph characterizing the intensity of syneresis;

The consistency of sour cream assess consistometer method of spreading. To do this, in the centre of the consistometer install hollow metal cylinder, fill it with product. Then the cylinder is lifted above the surface of the consistometer, and after two minutes measure the diameter of the spreading of sour cream.

The efficiency of homogenization is determined by centrifugation in a special pipette. The pipette through the lower capillary end is filled with the sample of cream to the top mark. The upper end of the pipette is closed with the finger, and the lower end put on the rubber stopper. Filled pipette is inserted symmetrically in the cartridges are centrifuge tubes to the periphery. After centrifugation, the pipette is removed and put vertically on the tube in the lower end. Then pipette carefully, without turning and shaking, drained the lower part of the product to the lower level, which closed with a finger of the left hand the upper opening of the pipette, and the right to remove the rubber plug from the lower end of the pipette. The merged product will determine the fat content. Homogeneity is calculated by the formula:

Э_г = 100 Ж_н /Ж_пр,

where , Э_г is the degree of homogenization, %; Ж_н – mass fraction of fat in the lower layer of the product discharged from the pipette %; Ж_пр – fat content in product, %.

Study of the effect of mode of homogenization to the consistency of sour cream. Pasteurized cream is cooled to a temperature of 70 ºC and homogenize, divide into 3-4 pieces and homogenizer at a pressure of 5, 10, 15 MPa. One part cream not homogenizers. Take samples of cream and determine the efficiency of homogenization. Of homogenised at different pressures and negalogenizirovanny cream produced under the same conditions cream.

After homogenization the cream immediately cooled to the fermentation temperature of 25-27 ° C and make the leaven of pure cultures for sour cream in an amount of 5 %. The mixture was stirred and left to ripen in the thermostat to clot formation. The stirring was repeated after 1 h after fermentation.

Upon reaching the titratable acidity 60-65 ºТ fermented cream is stirred and cooled to 5-6 ° C and kept for ripening. In the finished sour cream determine the mass fraction of fat, acidity, sinergeticheskie properties, the diameter of the spreading. Assess sensory characteristics.

Study of the effect of prior physical ripening of cream to the consistency of sour cream. Pasteurized cream was cooled to 25-26 ° C and divided into two equal parts. One of them make a bacterial ferment in the amount of 5 %, mix and leave to ripen in the thermostat to clot formation.

The second portion of cream is cooled to low temperature tap water and placed in the freezer refrigerator. After an hour take out the cream from the refrigerator, measure their temperature, slowly heated to a temperature of 25-26 ° C, make the leaven in the amount of 5 %, mix and leave to ripen in the thermostat to clot formation.

In both samples, the mixing was repeated after 1 h after fermentation. Upon reaching the titratable acidity 60-65 ºТ sour cream stand in the refrigerator. After cooling to 6 ° C carried out the quality assessment of sour cream determine the mass fraction of fat, acidity, diameter spreading. Assess sensory characteristics.

Determination acidity of sour cream.

1. On technical scales weigh in a beaker 5 g of sour cream, add 40 ml of water, 3 drops of phenolphthalein, mix well with a glass rod.

2. The mixture in a glass of titrate burettes 0.1N. NaOH solution until not disappear within 1 minute weak-pink color.

3. Read off the amount of alkali (ml) that went to the titration. Multiply the result by 20, we get acidity in Turner degrees. The discrepancy between two parallel determinations should be no more than 2 ° T.

The report on the done work

Make the scheme of the technological process of production of sour cream. Perform the necessary calculations. The results of observations and analyses recorded in the form presented in table 10.4. Build a graph characterizing the intensity of syneresis. Make a conclusion about the effect of homogenization on the consistency of sour cream.

Table 10.4

Number of the sample	The mode of homogenization		The efficiency of homogenization,%	Indicators of sour cream
	Temperature, ° С	Pressure, МПа		Acidity, ºТ	Consistency in diameter spread mm	Taste and aroma	Appearance
1
2
3
4