Why Does My Coffee Taste Sour?

Specialty coffee brewers like ourselves often get giddy at the prospect of having friends try our brew after we’ve practiced for days or even weeks. We get to that pivotal moment and brew coffee for our friends, only to have them look at us and say “oof, it’s quite sour”. Don’t let that comment get to you, it happens, but it does get you thinking about whether you’ve always been brewing sour coffee, if your coffee is just naturally sour, or if you just had a bad brew. Whichever the case, specialty coffee being “sour” is a common comment you’ll hear from first time specialty coffee drinkers who might be surprised by the acidity that comes from your new favorite beans, so we’re here to help you understand why your coffee could be tasting sour.

The Coffee Is Under-Extracted

Probably the most common reason why your coffee is sour has to do with the brew being under-extracted. There are 3 phases to coffee extraction, with the first part being where the sour notes of the coffee are extracted, so if your brew stops at this first phase, then you’re guaranteed a sour brew. It’s that crucial second phase where the sweet and complex notes of your coffee get extracted, so you’ll want to make sure you find this sweet spot during your brewing.

Your Coffee Was Ground Too Coarsely

Coffee that is ground finer extracts faster, so if your coffee is ground on the coarser side, it may take longer to get to that crucial second phase of extraction. As a result, your brew may come out on the sour side since the coffee hasn’t had enough time to really get extracted. Try a finer grind and it should help with getting out of that sour phase. Just make sure the coffee’s not ground too fine that the water isn’t able to interact with the coffee properly.

The Water’s Not Hot Enough

It goes without saying that the hotter the water, the quicker the extraction. What matters is you find the right temperature to brew your coffee where it isn’t too hot and causes over-extraction as a result (more on the bitter side). A temperature of 92-94 degrees Celsius is a good place to start. A good thing to note as well for water temperature is if the coffee is roasted darker, you can use a slightly lower temperature just to make sure you don’t over-extract.

The Coffee’s Too Fresh From Roast Date

During the roasting process, gasses but primarily carbon dioxide enter the roasted coffee bean. After the coffee is roasted, it begins a slow process known as degassing. It’s when the mostly carbon dioxide inside the bean is slowly released over time. When your coffee is too fresh from the roast date, say 1-6 days from the roast date, the coffee will still have too much carbon dioxide in it that it will push the water out, not allowing the coffee to be extracted properly as a result. This is partly why we ship out our coffees within that window of time when it is no longer too fresh from roast, so that you can begin brewing it without worrying about it tasting too fresh. It’s also when coffee is too fresh that it can taste sour because the gasses prevent the extraction from being properly done, so it’s mostly those sour notes that get extracted.