Reported August 2007

BACKGROUND: New research at The Ohio State University reveals some interesting insights into how clean dishes become using manual washing. Scientists found even when they washed dishes in cooler-than-recommended water, the bacteria levels on the dishware dropped to levels acceptable under current Food and Drug Administration regulations. This means restaurant employees can use a more comfortable dishwashing technique and still end up with clean dishes.

LATHER, RINSE, REPEAT: When restaurants manually wash dishes, they follow a three-step process. Dishes are washed and scrubbed in soapy water, rinsed with clean water, and finally soaked in water containing germ-killing sanitizers. Employees often use water cooler than 110-degrees Fahrenheit -- the minimum washing temperature recommended by the FDA -- because it is uncomfortably hot. The FDA also requires that washing cause a 100,000-fold drop in the amounts of bacteria on those dishes.

ABOUT THE EXPERIMENT: To investigate the effectiveness of lower-temperature dishwashing tactics, the OSU researchers coated dishes individually with cheese, eggs, jelly, lipstick and milk, and then added E-coli and Listeria innocua bacterial. Both these contaminants can survive for long periods of time if they make their way onto food dried onto dishes. If those dishes are not thoroughly washed, they can sometimes cause food-borne disease outbreaks. They let the food dry on the dishes for an hour, and then used different combinations of washing, rinsing and sanitizing before measuring the levels of microscopic organisms still clinging to the dishes, thereby determining the effectiveness of the cleaning.

WHAT THEY FOUND: The O.S.U. researchers found that washing dishes in hot dishwater, followed by soaking in extra sanitizers, eliminated almost all of the bacteria on them, even when coated with dried-on cheese. But dishes washed in soapy room-temperature water, rinsed, and then weakly sanitized with ammonium-based chemicals also achieved FDA-acceptable results. However, all dishes are not created equal. Compared to ceramic plates, steel knives, spoons and plastic trays, steel forks proved more stubborn about hanging onto bacterial contamination, largely because of the prongs. They recommended taking extra time to wash forks, especially those covered in sticky substances like cheese. Also, milk dried onto glasses protected bacteria more than any other food, although it is still unclear why that should be the case. Based on their findings, the OSU scientists recommend washing dishes right away before food dries, since otherwise bacteria will grow on them. It saves washing time and gets rid of problematic places where bacteria might be able to survive washing and drying.

The American Society for Microbiology contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Pam Frost Gorder
Public Information
The Ohio State University
(614) 292-9475
Gorder.1@osu.edu

For more information about bacteria and cleanliness:

American Society for Microbiology
Washington, DC 20036-2904
(202) 737-3600
http://asm.org

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