Yogurt

Yogurt Characteristicts and Processing
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JelekBagus
Ditulis oleh Administrator
Rabu, 30 Januari 2008
Yogurt in one of a family of cultured dairy products that include buttermilk, culture cream, dips, Kefir, Koumis and Acidophilus milk. All require good quality milk, high heat treatment of the milk, active & suitable bacterial cultures and good manufacturing practices.

All of these products are dependent upon the fact that casein (the major protein of milk) is insoluble at its isoelectric point (pH 4.6, where the net charge of the casein is 0.) Lactic acid bacteria product lactic acid which reduces the pH from the natural pH of milk (pH 6.5-6.6) to pH 4.6 and lower.
Some of the cultured milk products (buttermilk and sour cream and dips) utilized mesophillic lactic acid bacteria (Lactococcus lactis), whereas yogurt, Koumis, Kefir and acidophilus milk utilize lactic acid bacteria that grow best at about 40oC.

For Yogurt the fat content is generally reduced to about 1-2% and the milk solids increased by 1-4%. The milk is heated to temperatures well above standard pasteurization to:

* Destroy indigenous bacteria
* Improve the milk as a growth medium by reducing the oxidation/reduction potential
* Make a smoother bodied product which is smoother and with more resistance to "wheying-off" (syneresis)

Homogenization also provides for an improved body in the finished product. During homgenization, casein is attached to the surface of the fat globule. When the casein coagulated after acid production, the fat is a part of the continuous gel structure.
The cultures used for Yogurt are a !:1 blend of Lactobacillus bulgaricus and Lactococcus thermophilus. The organisms are synergistic, with each producing products required for the growth of the other. Plain yogurt has a "walnut" like flavor that is the result of formation of acetaldehyde during fermentation.

The majority of people do not like the taste of plain yogurt. The addition of sugar and fruit made a tremendous difference in the acceptance of Yogurt. Two style of fruit yogurt are the "Sundae" style where the fruit is on the bottom of the cup and "Swiss" style where the fruit is uniformly distributed through the product. The ingredients and processing of these two styles is different, as are the characteristics of the product.

After formulation, pasteurization and homogenization, the milk is cooled to the proper incubation temperature (about 40oC) and inoculated with 1- 1.5% starter culture. Incubation then proceeds until the desired acidity is reached. Different manufacturers use different pH end-points. The range is generally between pH 4.1 and 4.6.

Since the "Sundae" style Yogurt is incubated in the final package, the gel formed during coagulation is not disturbed and this product is firmer than the "Swiss" style Yogurt. Still care must be taken to avoid a lot of agitation of the package that would cause a break-down of the body.

"Swiss" style Yogurt is incubated in large vats (preferable cone shaped) and the curd must be broken for addition of the fruit and for packaging. The viscosity of Yogurt becomes less with mixing (non-Newtonian behavior) and generally stabilizers are added to provide for a heavier bodied product. Originally 0.5% gelatin was used as the stabilizer. Today, a number of stabilizer blends are available on the market.