Almost everyone has opened a container of yogurt and found a pool of liquid floating at the top. The watery substance doesn’t reduce the yogurt’s quality, but many consumers think that the presence of surface whey means that the yogurt is spoiled. As a result, most yogurt makers add stabilizers, such as pectin, to help keep the liquid from separating.

However, adding ingredients increases yogurt makers’ costs and may decrease consumer perception of yogurt as a health food, thereby limiting its markets. Now, a University of Wisconsin-Madison scientist is finding new ways to improve the body and texture of yogurt and reduce the whey separation defect without adding extra ingredients.

“The dilemma is that in order to position a product as a health food, it is desirable to use the least amount of ingredients possible while maintaining appearance and texture properties,” says John Lucey, a food scientist with the College of Agricultural and Life Sciences. “That”s why it is important for manufacturers to understand how to reduce the amount of stabilizers they use-even though they don”t make the yogurt less healthy. Reducing ingredients will also reduce costs for manufacturers.”

In the United States yogurt is marketed mostly as a treat for children. However, Lucey predicts that in time producers in the United States will be better able to position yogurt as a health food, as is done in Europe and Japan. Elsewhere in the world, consumers are aware of possible health benefits-such as reducing cholesterol and aiding digestion-from cultures in yogurt and other fermented milk foods, Lucey says. The cultures, called probiotics, are used in the United States, but so far most American consumers don”t fully understand yogurt”s benefits.

Lucey”s research focuses on the causes of the surface whey defect, which is formed when the yogurt”s gel structure is unstable and shrinks, forcing liquid out. He found that certain manufacturing conditions-such as a high incubation temperature and fast acidification rates-cause the gel to be less stable. “Reducing the incubation temperature from 113 degrees Fahrenheit to 104 degrees will create fewer defects without sacrificing much on production time,” Lucey says.

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 stirred yogurt, according to Lucey.

To improve yogurt quality, Lucey and his graduate student Wonjae Lee are developing simple tests that will allow yogurt makers to determine how their manufacturing and fermentation processes affect gel texture. These tests will help yogurt makers study and alter their existing production methods. They can also probe the mechanisms involved in the surface whey defect using a variety of approaches including rheology, to follow gel formation, and microscopy, to characterize the type of gel structure.

Lucey was recently invited to speak to industry representatives at the annual Cultured Products Forum in Milwaukee. “Many of them didn”t realize how conditions during production of the original gel affected the structure and defects in the final stirred product,” he said. “They were very interested and are receptive to the idea of exploring new ways to improve their current practices.”

The research on yogurt texture is supported by the State of Wisconsin and a grant from the College of Agricultural and Life Sciences.