Sourness in coffee isn't a safety issue—it's a flavor problem. You don't need to toss the batch, but you might want to brew a fresh cup if it's really unpleasant. The cause is under-extraction: your water didn't dissolve enough of the sugars and oils from the beans. That leaves you with sharp, acidic notes instead of balanced sweetness.

Common culprits are a grind that's too coarse, water that's too cool, a brew that finishes too fast, or a coffee-to-water ratio that's too weak. The good news? All of these are easy to fix without buying new gear.