Single-cup coffee brewers are as popular as ever, but if you’re not doing this important step regularly, you could be brewing trouble.
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Coffee hasn’t been the same since single-serve machines like Keurig hit the scene, and they’re still hugely popular. Forty-one percent of java drinkers own one, according to a 2018 National Coffee Association survey, and that number is on the rise. Now that Keurig, one of the top manufacturers of the machines, is designing an eco-friendly k-cup there’s really no reason not to use one. Compared to old-fashioned pots, they’re a faster and more convenient way to get your caffeine fix—no hot water or filters to discard, no carafe to wash.

In fact, they may be a little too convenient, because people often don’t realize that they need to clean them at all. But when microbiologists working for NSF International (formerly the National Sanitation Foundation), a public health and safety organization, swabbed different items in home kitchens and tested them for germs, coffee makers with water reservoirs had among the highest concentrations. “Water reservoirs are dark and damp, making them a prime location for mold or mildew to grow,” says Lisa Yakas, a microbiologist with NSF.

Changing the water regularly and rinsing or scrubbing the reservoir when you do is an easy way to prevent the growth of mold or mildew. However, in addition to regular cleaning, manufacturers like Keurig recommend a deep cleaning process known as descaling every three to six months. (Yakas suggests cleaning your coffeemaker monthly, or every 40-80 brew cycles if you’re more than a cup-a-day person or using a shared machine, as in an office). 

Why is descaling so important? In addition to mold and mildew, the other major issue with single-serve machines is that minerals naturally found in water—called "limescale" or just "scale"—can build up on the machine’s parts over time and hamper its performance. Descaling your Keurig prevents the buildup of scale and it also helps maintain the flavor quality of your coffee.

How to Descale a Keurig

Descaling your Keurig is pretty simple, really: Just fill the reservoir of your machine with descaling solution (available from Amazon, $8.73), then “brew” without using a k-cup. Use a mug to catch and discard the "brewed" water. Keurig recommends doing this twice, and then rinsing with regular tap water to remove any trace of the descaling solution. Don't have descaling solution? You can also use a diluted vinegar solution (equal parts water and distilled white vinegar) to descale your Keurig.

Some Keurig models (the Mini/Mini Plus and B/K130 brewers) have different instructions, which you can find here. In general, Yakas says it’s best to follow whatever maintenance and cleaning instructions the manufacturer recommends, since they have a vested interest in keeping their products working. But overall, that’s not much effort to put in for the reward of a perfectly brewed cup of coffee.