Why Is My Coffee Sour?

Why Is My Coffee Sour?

Sour coffee is caused by an excess amount of carbon dioxide in your beans. Good news though – it’s relatively easy to combat.


The first way to get rid of the sour-tasting coffee is to start with good quality, medium roast beans. Light roasted beans will always be on the sour side, while dark roasted beans will taste bitter.

Next, you want to allow your beans enough time to de-gas. De-gassing is a process that your bean goes through where the trapped carbon dioxide is slowly released. The carbon dioxide is actually what makes the coffee sour-tasting so it’s important to give the beans enough time to go through this process. Generally, 2 weeks after the roast date should be enough time for the beans to de-gas and your beans shouldn’t be sour. You may need to wait longer if it’s cooler weather – as a colder temperature slows down this process.

This leads us to two common misconceptions that are in the coffee industry;

  1. Fresh beans, right out of the roastery is the best to use.
  2. Store your beans in a refrigerator

Using fresh beans eliminates the de-gassing process so you are bound to get sour coffee, and cold temperatures slow down the process so you’ll be waiting much longer than 2 weeks to get nice tasting beans. Storing them in an airtight container in a cool cupboard is the way to go.

Run Your Shot

Another way to know that your beans are too fresh is by looking at the shot itself when you run it. There are some characteristics you can look out for that are a dead giveaway that your beans are still too fresh.

Sour/Fresh Shot

  • Uneven flow
  • Billowing
  • Bubbles
  • Blonde Colouring

A Good Shot

  • Even flow
  • Rich honey colour

For side by side videos of a good shot and a bad, fresh one, check out our ‘Why is my coffee sour?’ video on our YouTube channel; Coffee Beans Delivered.

Watch Here

Too little coffee

Another reason for your shot being sour is because there’s not enough coffee in your basket. A general guide to go by is that your basket should have 1-2g more coffee than your basket size. e.g. for a 22g basket, aim for 23-24g of coffee. (This is why it’s great to invest in scales to get this level of accuracy!) An underfilled basket causes sourness because there’s way too much pressure being applied to such a small amount of coffee.

Tamping too lightly

Tamping too lightly is also a factor which contributes to a sour shot. This is because, when tamping your coffee firmly and evenly, you interlock your shot which will create a strong barrier of coffee for the water to push against when running the shot. The resistance of the coffee from the water is what extracts the great coffee flavours you want. But- if there’s not enough resistance because there’s no strong barrier, the water will just easily run through the coffee and not extract any of those flavours, and hence, a sour shot. So always remember to tamp with a firm, even pressure. We have some great tamping blog posts you can check our below!

image of portafilter in background with overlay and text why you should never tap the side of your portafilter for title image

Coffee is too course

One other reason is that your coffee is simply too course! When adjusting your grinder, remember to only make small adjustments and keep troubleshooting until you get the shot right. For a more in-depth guide on how to dial your grinder, check out our blog post below!

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