Improve yogurt's texture without adding ingredients.

Most of us have opened a container of yogurt to find a pool of liquid floating at the top. Many consumers think that the presence of surface whey means that the yogurt is spoiled. As a result, most makers of yogurt add stabilizers, such as pectin, to help keep the liquid from separating.

However, adding ingredients increases the costs for yogurt makers, and may decrease consumer perception of yogurt as a health food. Now scientists at the University of Wisconsin-Madison are finding ways to improve the body and texture of yogurt and reduce the whey separation without adding extra ingredients.

The dilemma is that to position yogurt as a health food, it is desirable to use the least amount of ingredients possible while maintaining the product's appearance and texture properties. While for the most part yogurt is marketed in the United States as a children's treat, eventually producers will position the product as a health food, as is done in Europe and Japan.

The Wisconsin research is focusing on the causes of the surface whey defect, which occurs when the yogurt's gel structure is unstable and shrinks, forcing liquid out. Certain manufacturing conditions, such as high incubation temperatures and fast acidification rates, cause the gel to become less stable. Reducing the incubation temperature from 113 F to 104 F will create fewer defects without sacrificing much on production time.

Another challenge to U.S. yogurt makers is that their product is fermented and stirred in a large tank and then dispensed, along with fruit, into smaller containers for distribution. Yogurt makers are less aware of the important influence the original gel has on the final texture of the stirred yogurt.

To improve the quality of the yogurt, researchers have been developing simple tests that allow producers to determine how their manufacturing and fermentation processes affect gel texture. These tests help producers study and alter their existing production methodologies. They can also probe the mechanisms involved in the surface whey defect using a variety of approaches that involve rheology for following gel formation and microscopy for characterizing the type of gel structure. The scientists share their tests with industry through short courses.

Many manufacturers may not realize how conditions during production of the original gel affect the structure and defects in the final stirred product.

Further information. John Lucey, University of Wisconsin-Madison, Department of Food Science, 1605 Linden Dr., Madison, WI 53706; phone: [phone]; fax: [phone]; email: [e-mail].