How to Descale a Coffee Maker

Pour out any leftover water in the reservoir, dump used grounds and the paper filter from the basket on a drip machine, and remove the K-Cup pod and pod holder on a Keurig. Wash the carafe, filter basket, and drip tray in hot soapy water — this removes coffee oils that would otherwise mix with the descaler and create a sticky brown residue inside the lines. Rinse everything well and air-dry while you mix the descaler in step 2.

For a 12-cup drip maker, mix 4 cups (1 quart) distilled white vinegar with 4 cups water in a glass measuring cup — that is the standard 1:1 ratio. For a Keurig, fill the removable water reservoir halfway with vinegar, then top off to the MAX line with water. If you prefer citric acid, dissolve 2-3 teaspoons of food-grade citric acid powder per quart of warm water and stir until completely dissolved (about 30 seconds). Citric acid is the smarter choice for espresso machines and any model with an aluminum boiler.

Pour the mixed solution into the water reservoir up to the maximum fill line — do not exceed it, since the descaler expands slightly as it heats. Place an empty paper filter in the basket of a drip maker (this catches any loose scale flakes that flush out of the showerhead). On a Keurig, leave the K-Cup holder empty and put a large mug on the drip tray to catch the output.

Press the brew button and let the machine run until about half the reservoir has cycled through into the carafe (or mug for a Keurig). On a 12-cup drip, that is roughly 6 cups of liquid through; on a Keurig, two or three large 10-oz brews. Then turn the machine off — but leave the partially full carafe and the half-empty reservoir in place. The hot solution sitting inside the heating element and tubing is what does the actual descaling work.

Walk away for at least 30 minutes — an hour is better, especially if you have not descaled in a year or longer. The acid needs contact time to break down the mineral deposits; rushing this step is the most common reason a "descale" only restores half the lost performance. Set a kitchen timer or phone alarm so you do not forget. The longer the soak, the more scale comes free in step 6.

Turn the machine back on and let it run until the reservoir is empty. The output will be cloudy or have small white flakes — that is dissolved scale, and seeing it means the descaler worked. Pour the contents of the carafe down the drain (the diluted vinegar is also a fine drain cleaner), and dump out the catch mug for a Keurig. Do not drink any of this output even if it looks clear.

Empty the carafe back into the sink, then refill the reservoir to the MAX line with filtered or distilled water — never tap water, since municipal water is the source of the scale you just removed. Run a complete brew cycle with the empty paper filter still in place. Pour out the rinse water and repeat with another full reservoir. The second pass is critical: vinegar absorbs into rubber gaskets and plastic, and one rinse rarely flushes it all out.

Run one more full reservoir of fresh water through the machine. After the cycle ends, pour a small amount of the rinse water into a clean cup and smell it — there should be no detectable vinegar or sour scent. If you can still smell vinegar, run a fourth and even fifth rinse cycle. Citric acid users typically only need 2 rinse cycles; vinegar users often need 3-4.