“Sponges are usually the dirtiest thing in the kitchen and difficult to keep clean,” says microbiologist Manan Sharma of the United States Department of Agriculture’s Food Safety Laboratory in Beltsville, Maryland.
That’s a bold statement considering how much potential for mess there is in a kitchen.
A recent survey of U.S. homes found 77 percent of the sponges and dish cloths contained coliform bacteria, 86 percent had yeast and mold, and 18 percent had Staph bacteria. The survey was conducted by NSF International, a non-profit agency that sets safety standards for water filters and other equipment.
Why are sponges so dirty? “They come into contact with food residues that can build up in them and that provide nutrients for bacteria and other microorganisms to grow,” explains Sharma.
What’s more, sponges are often wet and are left in damp areas in or near the sink, which are ideal conditions for germs to multiply. In such ideal conditions, bacteria can double at a rate of every 10 to 30 minutes.
“They also have many nooks and crannies, which can be great places for germs to multiply,” notes NSF microbiologist Rob Donofrio, who adds that “sponges are typically not properly — or regularly — sanitized before their next use.”
That’s why the Food and Drug Administration’s Food Code prohibits restaurants from using sponges to make the final wipe of surfaces that come into contact with food.
Even though they know how to sanitize a sponge and are generally well equipped for sanitizing food contact surfaces, restaurants have to use a clean cloth rather than a sponge.
“A safe kitchen is a dry kitchen where there are no wet sponges and no wet towels for bacteria to grow overnight,” says O. Peter Snyder, whose Hospitality Institute of Technology and Management in St. Paul, Minnesota, provides training for the food and restaurant industries in sound food-safety practices.
Keep your kitchen safe with these simple tips
“Microwaving your wet sponge for one minute gets rid of a significant portion of the bacteria,” USDA’s Manan Sharma suggests.
After Sharma and his colleagues soaked sponges for two days in a slurry of ground beef and soy broth, microwaving at full power for one minute was the most effective way of killing the bacteria in the sponges. Running them through the dishwasher killed almost as many bugs.
What doesn’t work to sanitize sponges
“Just rinsing and squeezing out a sponge under running water is not going to do a whole lot,” according to Sharma. And soaking sponges in 10 percent bleach (about twice as concentrated as household bleach) for three minutes or in lemon juice or water for one minute wasn’t much better than doing nothing in USDA’s study.
Don’t try to microwave sponges that have metal in them, cautions Sharma. “And make sure the sponge is wet so it won’t catch fire.”
If you don’t want to go through all of this to keep your sponges clean, keep a supply of clean dish cloths handy. Start out each morning with a fresh, dry one. At the end of the day, toss the used cloth into the laundry hamper.
Want to learn more about keeping your kitchen safe?
- Watch out for bacteria in your sponges. See: The Dangers of Sponges and Dish Cloths
- Follow these food safety tips to keep your family healthy. See: Food Safety Tips for Packing and Unpacking Your Food
- How to clean and reorganize your refrigerator. See: Read These Important Food Safety Tips for Cleaning Your Refrigerator
Do you use sponges in your kitchen? Please share in the comments if you have tips on how to sanitize a sponge.
This post was originally published in 2012, and is updated regularly.