Why does my homemade coffee taste bitter?

For me it was the water temperature for the longest time - I'd just pour boiling water straight onto the beans and wonder why it tasted so bitter. If the water's too hot, you're extracting way too many bitter compounds. Try it around 90-95 degrees, that makes a huge difference.

Wait, I wouldn't just blame the usual suspects! Sure, overextraction and water that's too hot play a role, but often it's the coffee beans themselves. How old is your coffee? If it's been sitting around for a while or wasn't stored properly (so not airtight and protected from light), it oxidizes and gets bitter. Even the best brewing method won't save it then!

And one more thing: How fine are you grinding your beans? If the powder is too fine, you're massively increasing the surface area and the coffee extracts too quickly. That's also a kind of overextraction, just not because of time. Try making the grind a bit coarser - not quite as coarse as for a French press, but noticeably coarser than espresso powder. That makes a huge difference for me personally!

And try not using water that's boiling hot either. Around 85-90°C is just more pleasant for most coffees. If you only have hot water from the kettle, just let it cool for a minute before you pour it in. For me, that together with better beans and the right grind completely got rid of the bitterness!

Storage is often overlooked, but it plays a huge role. If your beans sit around too long or aren't sealed airtight, they oxidize and automatically get more bitter - and then even the perfect brew time won't help. I noticed this at home when I grabbed an opened package from the pantry and wondered why the coffee suddenly tasted totally different. Since then, I store my beans in an airtight container in the dark, and the difference is crazy.

The second thing the others mentioned is obviously right too - over-extraction and water temperature are real factors. But if you've already got those dialed in and the coffee still tastes bitter, I'd question how fresh your beans actually are. Check the roast date on the package? Ideally they shouldn't be older than two or three weeks. The older they get, the more bitter compounds come out, no matter how carefully you prepare them.

Are you using pre-ground coffee or grinding the beans yourself?

The bitterness is actually often coming from several factors at once - but one big point that's easy to overlook: a lot of people just use too much coffee powder per cup. That's not the same as over-extraction, it's more of a concentration thing. If you're putting too much coffee relative to the amount of water, of course it'll taste bitter. Try reducing the amount a bit and see if it tastes better. The water also shouldn't be boiling hot - more like 90-95°C if you can control it. And the brewing time depends on your method (filter coffee, espresso, French press?) - depending on that you should adjust things accordingly.

Another important point: have you cleaned your coffee machine or equipment recently? If oils and old coffee particles build up in the machine, every new coffee will taste bitter. That happens surprisingly fast with filter coffee machines. Just rinse it regularly with hot water or do a thorough cleaning every couple of weeks - that makes a huge difference.