Sour or lemony taste is one of the first concerns of many espresso novices. A sour taste suggests the coffee was under-extracted (too much water flowed too quickly through the grounds to pull out the sugars). Before throwing out your beans, give it a test run with a slightly finer grind. Pay attention to the time between pressing the lever and the appearance of the liquid. If the water shoots out in a fast stream, giving a low volume and light color, the grind is too coarse. Try reducing the grind just a hair at a time and see if you can get the espresso to flow in a smooth, honey-like flow.
A second common issue can be found in the distribution, not the machine. When the surface of the coffee isn’t flat, water finds it’s way through the cracks and will under extract some sections and over extract others. This causes an acidity and a lack of body. Make sure to even the grounds out before tamping, ensuring the surface appears smooth and loose instead of lumpy. I like to give the grounds a little thump to settle the grounds before tamping with even, heavy pressure. Tamping at an angle or placing too much pressure in one area creates the pockets of space that you’re trying to avoid. If your final puck is cracked or broken at the edges, the distribution may be the issue.
Another important factor that affects the taste of the espresso is the temperature. If the machine or portafilter is not warmed up, the brewing water cools down on impact which affects the extraction. Let the machine warm up completely and do a quick shot of air to warm up the metal. It’s also important to warm up the cup itself, because a cold cup diminishes the sweetness of the espresso and causes the acidity to taste sharp. It only takes a few seconds to warm it up with hot water and it does make a difference. Once everything is warmed up, you will find that with the same amount of coffee and the same grind setting, you will get a more balanced flavor.
A classic error is adjusting multiple parameters at once. If you change the grind, dose, and tamp, you can’t tell which change actually had an effect. Consider each shot an experiment. Hold the amount of coffee fixed and only adjust the grind until the shot timing is roughly where you want it (i.e., about twenty-five seconds, as counted at a relaxed pace). Once the timing is stabilized, adjust dose or tamping force if necessary. By doing it this way, you develop a sense of what is happening, rather than flying blind.
To refine your shot over time, it’s much better to spend about fifteen minutes pulling two or three shots in succession every day rather than occasional long attempts. Pull a shot, drink it while it’s still hot, pull another, and so on. Pay attention to the acidity, of course, but also pay attention to the texture, the nose, and the aftertaste. Take a note on any shots you make changes to. Even if you think you can’t tell a difference, write down your perception of the shot. Over a few days of doing this, you might notice that your coffee tastes sweeter when you grind a bit finer, that the finish is smoother when you use longer preheating, or that the body is heavier when you apply consistent tamping pressure. Your shot will be much less sharply acidic than it used to be, and instead it will just be bright.