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Why does coffee taste sour?

Asked by Gregory V.

Topics: brew trouble, tasting coffee
Let's dig into some possible causes of the sour taste. One common cause is under extracting the coffee during the brewing process. This happens when not enough flavor is taken out of the coffee grounds while you are brewing. The longer coffee brews the more sugars are extracted from the grounds making the coffee taste sweeter. However, go too long and you end of with a bitter taste (over extraction). The second cause of a sour taste is more a matter of taste preference. If you are used to darker roasts, you might associate the fruit notes of a lighter roast as having a sour taste. I've even heard a coffee drinker refer to a fruity Ethiopian roast as tasting like someone poured orange juice in their coffee. If the sour taste is a matter of taste preference, I would recommend either sticking with darker roasts, or slowly working your way from darker roasts to medium and then Colombian/Brazilian coffees to Ethiopian. It's a great way to ease your palate into the full spectrum of coffee tastes. You don't have dive right into the deep end. If you think under extraction is the cause, here's a quick checklist of what can cause under extraction during the brewing process.

Causes of Under Extraction by Brewing Method
- Doing a pour over? Try a more medium grind size. If your grind size is too course, it can cause under extraction.

- Espresso or an AeroPress? Try a more fine grind size. Even a medium grind size can cause under extraction with a fast brewing method.

- French Press? You want a more course grind for a French Press since the grounds are steeping in water for a long time. A more common cause of under extraction is steeping the grounds for too short of a time. You should let the coffee steep for 4 minutes before pushing the plunger down and serving. 

I hope this checklist helps you diagnose the cause of your sour cup. If not, please shoot me an email at ryan@beanbox.co. We're happy to help!
Root out evil! Down with sourness in coffee! Our perception of sour taste in coffee has a number of roots: if coffee is over roasted (i.e. roasted too dark or roasted too fast); if the brew process leads to under extraction; if brewing happens too quickly after roasting (i.e. before it "settles"); if the water used has a pH of less than 7 (use pH neutral, filtered water); or if coffee remains in a heated state post extraction (think heat plates on drip brewers).

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