Nearly every bad cup of home coffee is one of two problems, and they’re opposites. Once you can tell them apart you can fix almost anything.
Water pulls flavor out of coffee in an order. The sweet, bright things come out first. The heavy, bitter things come out last. So you can stop too early, or you can carry on too long, and each tastes wrong in its own particular way.
Bitter, harsh, drying
You went too far. The water kept working after it had taken all the good things and started on the ones you didn’t want. It tastes heavy, slightly burnt, and leaves your mouth feeling dried out.
Fix it by giving the water less to work with, or less time to do it:
- Grind coarser. This is the big one.
- Brew for less time.
- Use slightly cooler water — off the boil, not boiling.
- Use a bit less coffee for the same water.
Sour, thin, sharp
You stopped too soon. Only the bright acidic things made it into the cup and none of the sweetness that balances them. It tastes lemony in a bad way, and watery underneath.
People almost always read this as “too strong” and add water, which makes it worse. Do the opposite:
- Grind finer.
- Brew for longer.
- Use hotter water.
- Make sure all the grounds actually got wet.
Change one thing at a time
The temptation is to change everything at once and hope. Then when it works you don’t know why, and when it doesn’t you know even less. Grind is the most powerful lever, so start there, move it one notch, and drink the result before touching anything else.
If it’s somehow both
Bitter andsour at the same time usually means your grounds aren’t all the same size — the small ones are giving everything up at once and going bitter while the big ones never really get started and stay sour. You are drinking both problems out of the same cup.
That’s a grinder problem rather than a technique problem, and it’s the reason we bang on about buying the grinder first.
Before you blame yourself
Check the coffee isn’t stale — nothing you do to a six-month-old bag will rescue it, and it goes off faster than you think. Check your ratio is roughly right, which is about two tablespoons per cup. And taste your tap water on its own. If it isn’t nice to drink, it won’t make nice coffee, which we wrote about in 2013.