Sour Espresso… it’s something that I’d say 90% of beginners run into when they first start making espresso at home. Let’s look at some of the things that can lead to this!
When I use the term “under-extracted”, I’m referring to how much of the coffee goodness you were able to pull from each individual ground of coffee. To put it simply, extraction relies on two things; temperature, and contact time. Think of cold brew. It uses low temperature, but long contact time to extract.
Espresso does the opposite. It uses high temperature (and pressure), and a very short contact time. The water is only briefly in contact with the coffee as it flows through on it’s way from the group head, to the filter basket. This is what makes dialing in espresso so touchy, as even a slight variation in flow rate represents a large percentage change to the overall contact time between the water and coffee.
When you taste sour espresso, it is due to under-extraction… meaning that the water flowed too quickly past each coffee particle, not giving it enough time to extract. Grinding finer ensures there is more contact time, and contact area, between the coffee and water, resulting in higher extraction, and a more rounded flavor in the cup.
Grind setting is not always the only reason for incorrect flow. If there is channeling happening through the puck (all the water is rushing through one area), this will also have a negative impact on extraction. A bottomless portafilter is the best way to determine if your flow troubles are a result of grind size, or because of channeling.
If you’ve already slowed your flow down considerably, increasing temperature will also allow you to increase extraction without impacting the flow rate, as it introduces more energy into the extraction reaction. And I’m not just talking about the temperature of the brew water itself. One of the biggest mistakes beginners make, is to brew with a cold, or lukewarm portafilter, which pulls heat away from the extraction, effectively lowering the brew temperature. Make sure your portafilter is hot to the touch before brewing. You can soak it in some boiling water if you’re impatient, but just make sure that it’s completely dry before adding in your grinds, and if you’re pulling a second shot, do not run the portafilter under water to wash it in between. Simply wipe out the grounds with a rag, and immediately grind for the second shot.
Finally we come to brew ratio. Even if you have a good flow rate, and good temperature, it doesn’t mean much if you don’t push enough water through.
eg// Want to brew a single cup of cold brew but use a whole cup of coffee grinds to do it? That’s going to be some pretty nasty tasting coffee. There isn’t enough water to fully extract the grinds… The brew ratio is wrong.
The same applies to espresso. As each ml of water passes through the puck, it can only pick up so much coffee goodness on it’s way through. In order to fully extract your coffee, you need to use an appropriate amount of water to do it. If you’re tasting sour espresso with good flow and good temperature, odds are you need to push more water through the puck.
One misconception I’d like to address is the difference between under-extracted, truly sour espresso, and naturally occurring acidity. In the world of coffee high-snobriety, acidity is something that is celebrated and searched for. A parallel can be drawn to people who enjoy drinking scotch. Smokey petey notes are a staple of the industry, but can come across as very offensive to those just starting out with the hobby. With espresso, much like with scotch, the flavours are very concentrated and intense, meaning that the acidic notes present in some coffees can often be interpreted as quite “sour” and unpleasant on some people’s palettes. I am one of these people. I much prefer a rich, sweet syrupy shot, over a light, fruity, acidic shot of espresso, the same way someone might prefer a sweet cherry bourbon over a smoky Isla scotch.
Because of this concentrating effect that espresso has on flavours, a coffee that tastes great when used in pour-over, might taste quite harsh when pulled as an espresso shot, and because acidity is more noticeably present in lighter roasts, espresso tends to be made with darker beans, as they are more easily extracted, and more rich and sweet in flavour profile. The main takeaway from this, is to ensure that you are in fact tasting a sour shot, and aren’t simply disagreeing with the flavour profile of a coffee you are actually properly extracting.
Choose the right coffee for your palette, darker coffees will generally express less acidity
Increase extraction by:
Grinding finer to slow the flow and increase contact time
Adding more heat to the extraction by using a hot portafilter and higher brew temp