Most coffee makers are crawling with germs and growing mold, experts say. Here's why

Adrianna Rodriguez | USA TODAY

Show Caption Hide Caption Simple tips for cleaning your coffee maker Are you an avid coffee drinker? Make sure you've got a clean coffee machine.

If you're an avid coffee drinker, you’re probably making multiple trips to the kitchen to get your fix. But have you ever thought about how dirty your home or office coffee maker can get after all those uses?

Whether it’s the single-serve Keurig, espresso Nespresso machine or a traditional coffee maker, it’s important to keep these appliances clean to prevent the growth of bacteria, yeast or even mold.

Lisa Yakas, senior product manager of Consumer Products at NSF International, formerly known as the National Sanitation Foundation, says that these appliances are relatively harmless as long as clients follow the manufacturer’s cleaning directions.

However, without routine cleaning, they can get pretty grimy.

Mold and yeast like to grow in your coffee maker

Yakas points to the water reservoir – the part of the coffee maker that stores water – as one of the dirtiest parts of the kitchen if not cleaned on a regular basis.

A NSF International study of kitchen products in 2011 found that 50% of the sampled reservoirs in coffee makers had mold or yeast.

“It wasn’t on their radar,” Yakas said of the families involved in the study.

According to the U.S. Food and Drug Administration, food borne yeast and mold can be a source of sensitivity for people with allergies and may even cause infections.

Yakas recommends to always empty out the unused water in the reservoir and leave the lid off to let it dry out.

“Some of these organisms like these moist and damp places, that’s where they like to grow,” Yakas said. “If you eliminate that moisture altogether… then you eliminate their conditions to grow.”

Her motto is “keep it dry and keep it clean.”

Other places germs appear in and around your coffee maker

Chuck Gerba, professor of microbiology at the University of Arizona, said coffee break rooms have more bacteria than restrooms in most office buildings.

If the office has a coffee pot, Gerba says the first thing that gets germiest is the coffee pot handle. However, on a single-use machine, he says the top of the machine where the people place the plastic pod has the most germs.

“When you use the machine, it could get in your coffee,” he said.

Gerba also said that another big source of germs are coffee cups, especially if they’re shared amongst co-workers. A 1997 study he co-authored examining office coffee cups found that E. coli and even fecal matter were found in some of the cups.

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According to Gerba, the sponges that people were using to clean out their cups were actually contaminating them. If the office has a dishwasher, he recommends using it.

“Dishwashers work great because you have a high temperature and it dries out,” he said.

However, if the sponge can’t be avoided, Gerba says it’s important to wipe the coffee cup dry with a paper towel instead of using a cloth or letting it dry out on a rack.

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How to clean your coffee maker: Keurig, Nespresso, Black & Decker, Mr. Coffee

Both Gerba and Yakas say that the heat from the coffee maker can kill most germs, but it shouldn't replace ritual cleaning or descaling, which should happen every one to six months depending on the manufacturer's recommendations.

“While it’s possible the heat of coffee brewing might kill some microbes, why take a chance?" Yakas said. "We think it’s best to go to the source and keep the coffee maker clean."

So, here's how to properly clean your coffee maker according to the product's manufacturer:

Keurig: Turn off the Keurig and empty out the water reservoir, removing the filter. Pour Keurig descaling solution into the reservoir. After pouring the entire solution in, fill the empty bottle with water and add that into the reservoir. Power the Keurig back on, place a mug, perform a cleansing brew using 10 oz. brew size and then pour out the contents of the mug. Repeat until the "add water" light comes on. Let the Keurig sit for about 30 minutes (with the power still on) and then rinse out the reservoir thoroughly. Fill the reservoir with fresh water and perform at least 12 cleansing brews.

Nespresso: Rinse and clean the water tank before filling it with fresh water and then put the water tank in place. Rinse the cup support and place a container of at least 0.5 liters under under the coffee outlet. Then open the machine head, let the used capsule be ejected, and empty and rinse the capsule container. Close the head and turn lever until in the "locked" position. Push the button three times within two seconds, the button should start blinking quickly. It will take less than two minutes for a flow to come out, then the cleaning procedure will run automatically for five minutes for three cycles. The company urges that consumers to not use any cleaning agents or vinegar in the process. The company offers their own descaling products to use instead.

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Black & Decker: The coffee maker will indicate when it's time for a cleaning cycle. Fill the reservoir with equal parts white vinegar and cold water, then place a paper filter into the filter basket and close the cover. Press the auto clean button on the control panel. About half of the liquid will pour into the pot right away, but the second half will take about 30 minutes. When the process is done, the pot should be full and the coffee maker will automatically shut off. Before brewing coffee again, run another cycle with just cold water.

Mr. Coffee: Some traditional coffee makers aren't programmable with a cleaning cycle, in which it's recommended to clean your coffee maker with the vinegar solution every 40 to 80 uses. Instead of using the auto clean button, turn on the coffee maker until the carafe is three cups full. Turn if off and wait 30 minutes, then turn it back on and brew the rest.

Gerba said that vinegar will clear out most of the mold and yeast, but it’s not considered to be a disinfectant by the U.S. Environmental and Protection Agency and doesn’t get rid of all the bacteria that can make a person sick.

That’s why Yakas recommends taking out each removable piece of the coffee maker and cleaning it by hand. Some coffee maker parts are dishwasher safe.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.