Yoghurt Manufature

YOGHURT MANUFACTURE
INTRODUCTION
Fermented milk products are made from high quality milk that has been heated to appropriate temperatures and cooled, then inoculated with Lactobacillus bulgarieus and Streptococcus thermophilus bacteria that produce lactic acid and the characteristic yoghurt flavor. Normally skimmed milk is added to obtain heavy bodied yoghurt.
During the inoculation process, acetylaldehyde is produced during their synergistic growth and the mother culture has a ratio of cocci to bacillus of 1:1 or 2:1.This balance can be maintained with the control of inoculation quantities, time of innoculation and temperatures.
Raw materials
Whole milk
Skim milk powder-2.5%
Sugar-6.5%
Starter Culture
Flavor/Colour
Procedure
1. Weigh the ingredients in the required proportions.
2. Mix skim milk powder wit h sugar thoroughly to increase dispersability.
3. Add the skim milk powder(SMP) and sugar mix to the raw milk and stir well
4. Sieve and pasteurize at a temperature of 90°c
5. Remove and hold for 30 minutes
6. Cool to 45°c in a water bath
7. Innoculate with culture(DVS-Thermophilic lactic culture)
8. Incubate at 45°c for 6 hours
9. Remove and put in the cold room overnight
10. Stir, add flavor and pack

Results
The yoghurt should have a pleasant aroma, the colour should be shiny ((attractive) and the taste good. The texture should be smooth, viscosity-thick and the flavor; slightly acidic.
Discussion
Yoghurt has pleasant sour as a result of bacteria action which leads to the breakdown of lactose into lactic acid. In yoghurt making, the product should have a firm, solid and uniform body and texture prior to stirring and only a few drops of whey on the surface should be allowed. Any presence of lumps or particles signifies poor stirring at the wrong time at the wrong time, more so, addition of milk powder and starch without pre-mixing can result into poor solution hence giving particles in the final product.Wheying off, may result from over heating and lack of enough or no starch to bind up water molecules.
Over heating may also bring about excessive destruction of proteins hence wheying off. Starch contributes to viscosity, thus viscosity can be affected both by starch and stirring process during incomplete fermentation process hence making the product less viscous. Over fermentation, leads to production of excess acids thus the sharp tastes cases. Normally, after incubation period, cooling is done to control the level of lactic acid in the product.
In the flavor production process ,starter cultures are composed of 2 types of bacteria, one type fermenting lactose into lactic acid and the other ferments citric acid to diacetyl volatile acids and carbon-dioxide in which diacetyl is responsible for flavor, thus citric acid, acetic acid and diacetyl are important for aroma compounds, citric acid is the raw materials for the diacetyl flavor. Hence in the process of flavor production, the lactic acid bacteria produces lactic acid which creates a better environment for the growth of the flavor producing bacteria, hence the flavor bacteria converts the citric acid to acetic acid which is converted to acetyl-methyl carbinol(AMC) and diacetyl-acetic acid, which is odorless but an ideal source of diacetyl that is responsible for desirable flavor and aroma. However the conversion process occurs if only considerable acid is present, failure to which AMC is converted to butylenes glycol. The SMP is first mixed with sugar to disperse the particles which facilitates dissolving in the raw milk, however the solubility of the skimmed milk powder may be enhanced by raising the temperature of the raw milk by heating.
Also, the SMP increases the total protein particles formation of the yoghurt and also increases the viscosity and the total soluble solids in the product; this also enhances the mouth feel of yoghurt increasing its acceptability.
Sugar is mainly added as a sweetener, but it also increases the total soluble solids.
During processing, the milk is heated to 90°c and held for 30 minutes. Heating or past or pasteurization is important as the pathogenic and spoilage bacteria are destroyed
Conclusion
Yoghurt can be improved by addition of herbal extracts.
In contrast to milk whose consumption is related with a variety of cancers, yoghurt protects against this disease, particularly breast cancer. Its content of active bacteria cultures and lactic acid partially explains this protective effect

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The writer is a graduate of Bsc.Food Science and Nutrition from JKUAT