Sour espresso, though a phenomenon that might be startling at first, is a relatively common occurrence. You might have a promising shot lined up with a beautiful aroma, but when you take a sip, you find that it tastes somehow sour or thin instead of rich and full. In most cases, this is a sign that your shot of espresso is under-extracted, which means that there is too much water and not enough coffee in your drink.
Making an espresso shot is all about passing hot water through compacted grounds at the right velocity. If the water is moving too fast, it won’t pick up all the sugars, but instead will mostly just carry the bright, acidic qualities of the shot into your demitasse. One of the simplest ways to check for under-extraction is to watch the shot as it pours into your cup. If the shot is coming out too fast and is particularly light in color, you probably need to grind your beans finer.
With coarser grinds, it is far too easy for the water to pass right through without picking up much of anything. So, give your grinder a few turns to make the grind a bit finer, and try another shot. Chances are you will notice a difference almost immediately. If the pour is slower and darker, it is likely that you are extracting more from your grounds. Another potential reason for sour espresso is that the grounds are not distributed evenly in the portafilter.
If they are not evenly distributed, the water will just tunnel through the grounds and bypass some areas, leading to an inconsistent shot. This shot will taste both sour and watery. To make sure the grounds are even, before tamping, gently rock the portafilter back and forth or give it a few taps to settle all of the grounds to the bottom of the filter. Then, use your finger or another tool to even out grounds that have clumped together, and tamp away. This will help ensure a more consistent extraction. To really get a feel for sour espresso and how to combat it, try this exercise.
For 15 minutes, pull three separate shots of espresso. The only variable you will change is the grind. Start with your current grind setting and taste it. Then, make it a bit finer, and pull another shot. Finally, make it just a bit finer and pull one last shot. As you gradually make each shot finer, you will be able to taste the espresso get progressively sweeter. With some practice, sour espresso becomes very easy to identify and correct. You won’t be playing a guessing game with your grind nearly as much, and you will be able to see by the speed and color of your shot whether or not it is extracting properly. Then, you will be able to taste and see the difference for yourself. With practice, you will find that your shots are sweeter and less sour, leading to a richer, more full-bodied cup of espresso.
