Sour Coffee? Read This…

Have you ever had a cup of sour coffee? It’s a pretty common problem, right up there with coffee tasting too bitter. Hint: it has something to do with extraction.

So why does coffee taste sour? In this article, I want to address the problem of sour coffee and offer a range of solutions to eliminate these unwelcome flavours.

What Makes Coffee Sour?

Sour coffee is a symptom of under-extraction during the brewing process. The good news is that this leaves the solution in your hands, as all you’ll need to do is make minor adjustments to how you’re brewing your coffee to avoid the unpleasantly sharp flavours of under-extracted coffee (1).

Sour vs Bitter Coffee: The Two Sides of the Extraction Coin

Coffee extraction occurs when the flavour compounds of the ground coffee beans are extracted with hot water.

Different compounds are extracted at different points of the brewing process, and in the same order every time (​3​​​).

First, the fats and acids are extracted, producing that oily, sour flavour. Next come the sugars, which serve to balance things out with their sweetness And finally, if you overdo it, the plant fibres will extract, allowing the bitter elements to come out to play.

The length of brew time is the major deciding factor here, with the two unwanted options ( sour and bitter) at opposite ends of the brewing spectrum.

Here’s a good visual of what over-extracted and under-extracted coffee can look like when using an espresso machine.

How to Fix Sour Coffee (Depending on your Brewing Method)

If you’re wondering what you can do to get rid of that awful taste in your coffee, it’s time to change up your grind size and brewing time to nail the perfect extraction.

Here is a great tip, tailored to some of the most common brewing methods (4):

The four primary ways you can influence extraction during coffee brewing are:

1 – Grind size: Finer grinds extract more flavour elements (including bitter components) than coarser grinds. Getting the coffee grinds just right for each bean, roast, and region is part of the art of coffee.

2 – Brewing time: Longer brewing time also enhances extraction. Note, though, that finer grinds in drip and pour over coffee methods will lengthen the extraction time, essentially doubling the effect. This can be critical if you’re using a Chemex, Hario, or another pour over coffee maker.

3 – Coffee-to-water ratio: While the coffee-to-water ratio mostly controls how much flavour is in the cup (whether the coffee tastes weak or strong), in some infusion methods the amount of coffee for the amount of water can affect sour/bitter balance.

4 – Water temperature: Nerd alert – chemical reactions double for every increase of 10 degrees Celsius, which means raising the water temperature will increase extraction. Be careful, though – too high a water temperature results in bitter or burned tasting coffee. Unless your kettle has a thermometer or a programmable heat setting, the rule of thumb is to take the kettle off the heat for 30 seconds before pouring – even the bloom, because too-hot water can start the over-extraction process even if it’s just during that initial pour. However, waiting too long will result in under-extracted coffee – which can taste, you guessed it, sour (5).

Here are our recommended solutions for fixing that sour flavour in several popular brewing methods. Where we offer more than one solution, the most likely culprit (and the easiest fix!) is listed first. Try that to start, and if you are still experiencing sour coffee, keep trying.

Don’t give up – coffee nirvana is in your grasp! With a little experimentation, you can brew coffee as good as you’ve ever tasted.

Problem: Sour French Press Coffee

SOLUTION 1:Brew longer for more extraction.

Make sure you’re giving the coffee at least 4 minutes of brew time. You can brew even longer than this (we’ve found some coffees that brew a perfect cup of French press after six minutes of steeping time), but eventually, you’re going to start getting that bitter flavour. It’s easy to over-extract coffee with a French press, so if you have leftover coffee after filling your cup(s), decanting is usually recommended. 

SOLUTION 2: Use a finer grind.

This is tricky with the French press, because too fine a grind is going to clog the mesh filter, or worse yet, fill your coffee cup with mud from the fine particles the mesh doesn’t capture. You may need to make a couple of experiments to find a “sweet spot” (see what we did there?) where the grinds are fine enough to produce a balanced brew, but coarse enough that you don’t end up chewing your morning mug. Download our coffee grind chart here.

SOLUTION 3:Try a different type of coffee.

Most French press lovers prefer the flavour of a dark roast – which tends to highlight the bitter elements more than a light roast does. If you’re using a light roast and coarse grind, you run the risk of under-extracting, which leads to that sour flavour dominating. Talk to your coffee roaster for suggestions.

Problem: Sour Cold Brew Coffee

SOLUTION 1: Use a finer grind.

Cold brew coffee is made similarly to French press (you can even make it in a French press!) and is steeped so long that it generally doesn’t have under-extraction issues. However, if you have sour cold brew coffee, chances are you’re not using a fine enough grind.

SOLUTION 2: Use a higher coffee-to-water ratio.

You might simply not be using enough coffee grounds. As a rule of thumb, you usually want between a 1:5 and 1:4 grounds-to-water ratio for cold brew. Remember that this is by weight, not by volume. If you’re not using a scale, check out our review of the five best coffee scales on the market.

Problem: Sour Drip or Pour Over Coffee

SOLUTION 1: Use a finer grind.

If you’re getting sour drip coffee, you may be using too coarse a grind. This can also lead to a sour taste in pour over coffee. Carefully increase the fineness of the grind until you achieve the balance of flavour that says you’ve got the extraction just so. Just remember, a finer grind also slows the drawdown, meaning it increases the extraction in two ways. You need to “sneak up on” the grind carefully.

SOLUTION 2: Increase your brew time.

This can be tricky on many pour overs, where the drawdown (the length of time it takes coffee to drain from the filter to the carafe) is an integral part of the design. In two of the most popular – the Chemex and the Hario – it’s easier to shorten the brew time than lengthen it, because once the coffee drains into the carafe, there’s no more water left for the extraction. If you have something like a Clever Dripper, try increasing your brew time in small increments – 15 to 30 seconds – and note the resulting flavour.

Problem: Sour Aeropress Coffee

SOLUTION 1: Use a finer grind.

​If your Aeropress coffee tastes sour or you keep pulling a sour espresso, again, try a finer grind size. Particularly with these methods, the extraction time can be mere seconds, which means the grind has to be fine enough to allow the extraction at a rapid pace.

SOLUTION 2: Use the Aeropress inverted method.

​What the heck does turning the Aeropress upside down have to do with sour coffee? A small amount of under-extracted coffee will dribble from the Aeropress brew chamber into your cup. To solve this, Aeropress fans have developed a way of brewing the coffee with the Aeropress upside down. When the brew cycle is over, you put your mug on top of the brew chamber, then flip the whole thing over (hopefully without showering yourself and your kitchen, office, or campsite with hot coffee and grounds). For all the details, check out our article here which walks you through the whole process.

One Last Note: On Sour Arabica Coffee

Another factor that can contribute to the perception of sourness is drinking lighter roasted, fruitier coffees – especially of the Arabica variety. If you are used to darker roasts but decide to try a light coffee, such as an Ethiopian or Kenyan single origin, the sharpness of the fruity flavours can be overwhelming. Not only that, but the fruity flavours can actually come across as sour, when really you are simply not used to fruitiness in coffee.

The easiest solution for this: turn your coffee grinder a few clicks towards the finer end of the grind scale. This will increase the extraction and provide a better-balanced cup. I like to move the grinder four clicks in the “new” direction because it gives a small range to back off if I’ve gone too far. Be sure to make notes on the setting you like best, so you can repeat it next time.

So, Why is my Coffee Sour?

Extraction, extraction, extraction. If your coffee is under-extracted, it’s going to taste sour.

Fortunately, it’s an easy problem to fix. Just tinker with your brewing method a bit and see if you can’t dial things in to get that perfect cup of joe! If you’re dealing with or have conquered this problem in the past, comment with your experience.  Also, please consider sharing the post so that we can save as many innocent sour coffee drinking victims as possible.