UT Researcher Makes Cider Safer

KNOXVILLE — A University of Tennessee researcher has developed a way to kill harmful bacteria that can contaminate fresh-pressed cider.

Dr. David Golden

Dr. David Golden

Dr. David Golden, a microbiologist in UT’s Agricultural Experiment Station, has developed an alternative to pasteurization that bubbles ozone through the cider to destroy E. coli and other microbes that can cause illness and death in humans.

“We’re treating the juices with ozone, which is just a form of oxygen. It’s basically bubbled through the juice while the juice is mixed,” Golden said. “We’ve had very good success in reducing very, very high numbers of E. coli and salmonella from cider and orange juice.”

The ozone method is expected to benefit small commercial producers of cider, who are facing new safety requirements from the U.S. Food and Drug Administration after contaminated cider killed a child and sickened more than 60 people in the Pacific Northwest in 1996, Golden said. In November 1999, the FDA began requiring all unpasteurized fruit juices to carry a label warning of the health dangers of drinking contaminated juices.

The new technology is a safe alternative to pasteurization, which involves heating a liquid until all the pathogens are killed, Golden said. In the case of cider, the heat of pasteurization destroys the fresh flavor of the juice. Ozone treatment is also much less expensive than pasteurization for cider mills and farmers markets, he said.

“Cider producers are very interested in our study,” Golden said. “Some in Indiana and Minnesota are already using an ozone treatment for their own protection.”

Researchers suspect that E. coli contamination results when apples that fall to the ground are contaminated with manure from cows grazing in the orchards, he said.

Ozone, a molecule made up of three oxygen atoms, purifies cider by breaking down fats in the cell membranes of harmful bacteria Golden said. The flavor of the apple juice is not affected by the process, he said.

Ozone breathed as a gas can be toxic, but when bubbled through juice it breaks down into a stable two-atom oxygen molecule, which is the usual state of the element, Golden said.

“The ozone very quickly dissipates and is gone,” he said.