Sour espresso: why it happens and how to fix it

Sour espresso is one of the most common complaints we hear from customers. Very often the beans are not to blame: the shot is simply under-extracted, so the water has not pulled enough sweetness and depth out of the coffee. Roast level, the coffee itself and the state of your machine matter too. Here is how to tell what is going on and what to change on an espresso machine or a bean-to-cup machine.

Pleasant acidity and sour coffee are not the same thing

Good acidity tastes like fruit: apple, citrus, redcurrant. It is bright but clean, and balanced by sweetness. You will find it in light-roasted coffees from Kenya or Ethiopia.

Sour coffee is different. The acidity is sharp and takes over the cup, sweetness is hard to find and the aroma feels flat. Sometimes there is also some astringency or a salty edge. That usually means something went wrong during brewing. We explain acidity itself in more detail in Acidity in coffee.

A common cause: under-extracted espresso

Different compounds dissolve from coffee at different rates. When extraction is too low, acidity can dominate the sweetness and bitterness that normally balance it. It is not as simple as “acids first, sugars last”, but in practice a shot that ran too fast or was brewed with water that was too cool usually tastes sour and hollow.

In The Professional Barista’s Handbook, Scott Rao links under-extraction with an underdeveloped taste and low brew temperature with sour espresso. Over-extraction, on the other hand, brings bitterness and astringency. Sour and bitter often point to opposite extraction errors, although with channeling you can get both in the same cup. Bitterness has its own article: Why is coffee bitter?

Why is my espresso sour? 6 things to check

1. Grind too coarse. Coarse particles give the water less resistance, so it runs through too quickly and extraction stays low. If a 1:2 shot is done in 15-20 seconds and tastes sour, grind finer. Make small changes and check time and taste after each one.

2. Shot too short. For a double espresso at 1:2, 25-30 seconds is a good starting point. If the same dose and ratio run much faster, expect more sourness. Common reasons for fast shots are covered in Why is my espresso running too fast?

3. Not enough water for the dose. A 1:1 ristretto usually extracts less than a 1:2 espresso from the same beans and often tastes sourer. If the time looks fine but the shot is still sour, try a longer ratio, for example 40 g out from 18 g in instead of 36 g. More on this in Espresso ratio: what does 1:2 mean?

4. Water too cool. Cooler water dissolves coffee compounds more slowly. Most espresso machines brew with water at around 90-96°C. If yours has a PID, raise it by 1-2°C and taste again. Warm up the machine and the portafilter before the first shot: a cold portafilter steals heat from the water.

5. Uneven tamping and channeling. If the coffee is unevenly distributed in the basket or tamped at an angle, water finds the easiest path and forms channels. Coffee along those channels over-extracts while the rest under-extracts, so the shot can taste sour, bitter and astringent at once. Distribute the grounds evenly and keep the tamper level.

6. Dose too small for the basket. Too little coffee offers less resistance, so water flows faster and extraction drops. Match the dose to the basket: start with 18 g in an 18 g basket, then check flow and taste. We look at dose in Espresso dose: 18, 20 or 22 g?

When the coffee itself is the reason

Sometimes the machine is dialled in well and the espresso still tastes too sour. Then it may simply be the profile of the coffee or its roast level.

Light roasts for espresso. Light-roasted coffees usually have more pronounced acidity, and the beans are harder and less soluble. They can make excellent espresso, but they need careful dialling in. On a bean-to-cup machine with limited settings, sourness is hard to avoid. We roast our light coffees from Kenya and Ethiopia mainly for pour-over and filter machines.

Origin and processing. Many coffees from Kenya, Ethiopia and high-altitude Central America are known for bright acidity. Among coffees from Brazil, India or Peru it is easier to find milder beans with chocolate and nut notes. Origin alone does not decide the cup, though: variety, altitude, processing and roast all play a part.

Very fresh coffee. Right after roasting, beans hold a lot of CO2, which can make espresso extraction unstable. Give them at least a few days to rest. The ideal time depends on the coffee and the roast. More in Freshly roasted coffee: when should you drink it?

Which coffee is not sour in an espresso machine?

If you just do not enjoy acidity, go for low-acidity coffees with a medium or darker roast. We have a whole low-acidity coffee category. These are the ones we recommend most often for espresso:

India Monsooned Malabar has an unusual story. For around 12-16 weeks the green beans are exposed to humid monsoon air in open warehouses and regularly turned and repacked. They swell, turn pale and develop their typical low-acidity character. The espresso is thick and mellow, with cocoa and spice.

Not sure where to start? Try the low-acidity coffee set, 4 × 250 g, brew each one on your machine and pick a favourite. More ideas in Best low-acid coffee beans.

Sour coffee from a bean-to-cup machine: what to adjust

An automatic machine gives you fewer controls than a traditional espresso machine, but a few settings still help.

• Finer grind. Move the grinder one step finer and brew 2-3 coffees before judging. On many machines you can only change the grind while the grinder is running.
• Higher temperature. If there is a temperature setting, raise it one level and compare.
• Coffee strength. A larger dose gives a stronger cup, but does not always reduce sourness. If the coffee is already strong and sour, grind finer first.
• Long coffee. If a long coffee tastes watery or bitter, brew an espresso and add hot water separately, as for an americano. If the espresso itself is sour, fix the extraction first.
• The right beans. If you do not like acidity, choose medium-roasted, low-acidity coffees for your bean-to-cup machine.

Water and machine condition

Espresso is mostly water, so water chemistry matters a lot. What neutralises acids is mainly the water’s alkalinity, largely its bicarbonate content. Water with very low alkalinity buffers acids poorly, so coffee can taste sourer. Too much alkalinity flattens fruity notes, and very hard water encourages scale in the machine. In the cafés where we install machines, we fit filters that keep water composition stable.

Cleanliness matters too. Coffee residue in the basket and group head disrupts flow and spoils taste, and scale in the water circuit makes temperature less stable. Clean the group, basket and portafilter regularly and descale according to the manufacturer’s instructions. Check the machine before you blame the beans.

How to fix sour espresso, step by step

1. Warm up the machine and the portafilter.
2. Weigh a dose that matches the basket, for example 18 g in an 18 g basket.
3. Aim for a 1:2 ratio, so 36 g of espresso.
4. Time the shot. If it runs clearly faster than 25 seconds and tastes sour, grind finer.
5. If the time is right but the shot is still sour, extend the ratio to 1:2.2-1:2.5 or raise the temperature by 1-2°C.
6. Change one thing at a time and taste after every change.
7. If nothing helps, switch to a low-acidity coffee.

Running a café? Our guide How to dial in a coffee grinder in a café will help too.