How to Sanitize a Sponge: Are Your Kitchen Sponges Safe?

how to sanitize a sponge“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.

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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?

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.

4 Replies to “How to Sanitize a Sponge: Are Your Kitchen Sponges Safe?”

  1. I have done this for years. Tip from a magazine. Soak sponge in 1 cup of water with 1 tsp lemon juice for a few seconds. Heat in microwave for 1 minute. Let cool for 5 minutes before removing. The acid in the juice works with the heat to kill bacteria. Leaves your sponge germ free ( almost ) and smelling great !

    1. From Nutrition Action Healthletter: As the article explained, lemon juice doesn’t do much to destroy germs in sponges. It’s the microwaving that does the job. But lemon juice may be why your sponges smell great!

  2. I often put a sponge in my steel sink and pour water that’s boiling or just below boiling point slowly over it. I let it sit in my sink till I can handle it, squeeze it as dry as possible, and put it somewhere where the whole surface is exposed to air so it dries the rest of the way and avoids smelling sour. Hope this is effective, but perhaps I should try the method mentioned above instead.

  3. I put my kitchen sponge in with a load in the clothes washer, along with some oxygen bleach (which I use anyway. No research to support this, but sponge come out clean and odor-free. This could be better than the microwave method, since it removes deposits from the sponge.

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