Why sponges are the riskiest item in your kitchen

“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.

sponge-smallThat was true in the NSF International survey of U.S. homes, where 77 percent of the sponges and dish cloths contained coliform bacteria, 86 percent had yeast and mold, and 18 percent had Staph bacteria. (Coliform bacteria may indicate fecal contamination.)  NSF International is 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 left in damp areas in or near the sink, which are ideal conditions for germs to multiply.

“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.”

Restaurant sponges

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.

“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.

How to clean your sponges

“Just rinsing and squeezing out a sponge under running water is not going to do a whole lot,” says Sharma. “But microwaving your wet sponge for one minute gets rid of a significant portion of the bacteria.”

After Sharma and his colleagues at the USDA 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. Soaking them 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.

A recent study by the Good Housekeeping Institute found that soaking sponges for five minutes in bleach was the most effective way of cleaning sponges. However, what the Institute did— mixing three-quarters of a cup of bleach in a gallon of water—may be more than what most people are willing to do. Its study found that cleaning sponges in a microwave oven or in the dishwasher with dry heating was nearly as effective as the bleach.

Kitchen Sponge

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 that to keep your sponges clean, your best bet is to keep a supply of clean dish cloths handy. Start out each morning with a fresh, dry one and at the end of the day toss the used cloth into the laundry hamper.

Sources:  Dairy Food Environ. Sanitation 21: 997, 2001. Am. J. Infect. Control 17: 83, 1989.

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9 Replies to “Why sponges are the riskiest item in your kitchen”

  1. I have asked this question a few times and never received an answer. When sanitizing dish cloths or sponges in the microwave, is there any contamination residue left on microwave walls? In other words, do you then have to clean the microwave somehow?Seems to me it would be safer just to replace the cloth or sponge daily as you also suggest.

    1. I would think you don’t have to worry about germs in the microwave itself from the wet sponge and they would die also when being radiated. Microwaves move water molecules and that is how they heat food and also the germs die because bacteria are mostly water and they boil to death. This occurs to those on the surface of the microwave plate as well as in the sponge.

  2. I use one sponge for washing my dishes and another one for wiping my countertop. When I am done washing dishes I rinse both sponges with boiling hot water-I wear two pairs of rubber gloves when I do that. I am more concerned about food safety in my kitchen than I am my sponges, especially after getting meat and poultry ready to go in the oven or be cooked on the stove top or in the crockpot. I really want to be sure my sink and countertop are sanitized then.

  3. I have soaked my sponges in Clorox water and lots of soap suds..I’ll remember to put them in microwave after this.I like using a sponge with the scrubby back.

  4. I have a sponge and a dishcloth in my kitchen, but they have completely separate uses. the dishcloth is for wiping the counter, etc. and the sponge is strictly for wiping up spills from the floor. If they are put into the dishwasher, is there any contamination conveyed to the dishes or the inside of the dishwasher?

  5. when you get clorox if you buy splashless it says not for sanitizing , i called the company and was told that splashless and lemon are not for sanitizing but the others are.

  6. I use a Handi Wipe which I sanitize on a daily basis by microwaving the damp Handi Wipe in a silicone food storage bag for 1.5 minutes.

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