Unveiling the secrets lurking in your coffee maker

The hidden truth

The concern is not just an unpleasant smell or an old coffee taste. In its household germ research, NSF identified coffee reservoirs as one of the places where microorganisms could build up.

Moisture and overlooked surfaces help explain why. Still, a finding in a household study does not tell you what is inside your own machine, and detecting microorganisms is not the same as proving that a cup will make someone ill. The useful lesson is less dramatic: the parts that hold water need cleaning too, even when the appliance heats water during brewing.