Why does coffee taste sour?

Sour coffee comes down to two things: (1) bad beans and (2) bad brewing.

If the beans are under-roasted, they’ll taste grassy and sour. If they’re old and stale, they’ll have a really sharp lemony flavour. But, chances are, you’re beans are fine—which means you need to make a small adjustment or two to how you make your coffee.

Sour coffee is usually under-extracted coffee. Essentially, the beans didn’t get brewed enough… and so not all the flavours are there to balance out the acids.

We break why this happens and the stages of extraction (the acids come first) in this blog, if you’re curious.

Here’s how under-extraction tends to happen at home:


  • Your beans are ground too coarsely. Fine grounds extract quickly, but large ones take longer because the water needs more time to get into the center of each particle (you know, science). An overly coarse grind size could simply mean each particle isn’t getting the time it needs for a balanced extraction.


  • Your brew time was too short. You want to brew long enough to bring out the flavors that will calm down the acids and hit that sweet spot of flavor. With a french press, maybe you plunged the filter down too early. With a pour over cone, maybe you poured your water too fast and it drained too quickly.


  • Your water is on the cool side. It’s been proved that the best water for coffee is between 195 and 205 degrees. If it gets below that, it won’t extract the good stuff from the coffee as quickly as it needs to, which can lead to under-extraction.


  • You didn’t use enough water. Your coffee to water ratio matters a lot, and if you don’t give each ground the right amount of water it needs to extract a balanced brew, you’ll naturally end up with under-extracted coffee.

Note: If you normally buy dark roast coffee from the grocery store, you’ll probably find that most “specialty coffee” beans taste more acidic than you’re used to.

That’s by design—leaving some of that tang and zing helps enhance the other flavors.

We suggest giving a little time for your taste buds to adjust. Sometimes it takes a few cups, but your tongue will eventually realize that the extra acidity actually helps bring out good flavors that you can’t find in super-dark beans.

questions about drinking coffee