Best ways to clean kitchen sponges.

At the Agricultural Research Service (ARS) Food Technology and Safety Laboratory in Beltsville, Maryland, scientists have tested several methods for reducing risks from harmful microbes hiding in reused sponges.

Microbiologists Manan Sharma and Cheryl Mudd and two student interns did the testing. First, they soaked sponges at room temperature for 48 hours in a solution made from ground beef and lab growth medium to obtain a high level of microbes (20 million per sponge) and simulate a very dirty sponge.

Then they treated each sponge in one of five ways: 1) soaked it for 3 minutes in a 10 percent chlorine bleach solution, 2) soaked it in lemon juice or deionized water for 1 minute, 3) heated it in a microwave for 1 minute, 4) placed it in a dishwasher operating with a drying cycle, or 5) left it untreated.

The scientists chose these methods because the methods are commonly used in household kitchens. They found that between 37 and 87 percent of bacteria were killed in the sponges soaked in 10 percent bleach solution, lemon juice, or deionized water--and in those left untreated. Enough bacteria remained to potentially cause disease.

Microwaving sponges killed 99.99999 percent of the bacteria, while dishwashing killed 99.9998 percent of the bacteria.

As for yeasts and molds, the sponges treated in the microwave oven or the dishwasher were found to retain less than 1 percent (0.00001 percent). Between 6.7 and 63 percent of yeasts and molds survived on sponges that were soaked in bleach, lemon juice, or deionized water or that were left untreated.

Thus, microwave heating and dishwashing with a drying cycle proved to be the most effective methods for inactivating bacteria, yeasts, and molds on sponges. These simple and convenient treatments can help ensure that contaminated sponges don't spread foodborne pathogens around the household kitchens of today's busy families.