You took the time to buy great beans, you have the fancy kettle, but the first sip makes you wince. It’s either unpleasantly sharp or harshly dry. Before you blame the beans, let’s look at extraction. Extraction is the process of pulling flavor out of the coffee grounds. If you pull too much, it's "over-extracted." Too little, and it's "under-extracted."
1. Why is my coffee sour? (Under-extraction)
If your coffee tastes salty, thin, or unpleasantly acidic (like a lemon with no sweetness), you haven't pulled enough flavor out.
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The Fix: Your grind might be too coarse. Try a finer setting to slow down the water. Alternatively, make sure your water is hot enough. Aim for 195°F to 205°F.
2. Why is my coffee bitter? (Over-extraction)
If your coffee leaves a dry, "ashy" feeling on your tongue or tastes like burnt toast, you’ve pulled out the bad stuff.
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The Fix: Your grind is likely too fine, causing the water to sit in the grounds too long. Coarsen it up. You might also be using water that is boiling ($212^\circ F$), which "scorches" the delicate flavor compounds.
3. The Water Quality Factor
Coffee is 98% water. If your tap water tastes like chlorine or has high mineral "hardness," your coffee will never taste like the roaster intended.
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The Pro-Tip: Use filtered water. You don't need a lab-grade system; a simple charcoal filter pitcher will dramatically "clean up" the flavor profile of your cup.
4. Clean Your Gear
Coffee oils are sticky. If you haven't deep-cleaned your French Press or your drip machine’s carafe lately, you’re tasting last week’s stale oils mixed with today’s fresh brew. A quick scrub with scentless soap makes a world of difference.