The espresso takes 12 seconds to flow, tastes sour and seems thin - even though the beans are actually good? Then the problem is often not the coffee brand, but the grinder. If you can set the espresso grind yourself, you can bring out significantly more body, crema and balance from Italian beans. The good news: you don't need barista training for this. A clear approach, a few test shots and a little patience are enough.
Why the grind size determines your espresso
When making espresso, hot water flows under pressure through a compact coffee puck. How quickly it passes through is determined primarily by the size of the ground particles. Finely ground coffee slows the water down more, while coarsely ground coffee lets it pass through faster.
If the grind is too coarse, the water encounters too little resistance. The shot rushes through, and the espresso often tastes sharp, sour or watery. If it is too fine, the water gets backed up. The shot only drips slowly, can taste bitter, dry or burnt, and puts unnecessary strain on the machine.
The right grind size is therefore not a fixed value on the dial. It depends on the bean, roast, age of the beans, humidity, grinder and portafilter. Even with the same variety, a small adjustment may be necessary after a few days. This is normal and not a sign that something is wrong with your machine.
Set the espresso grind yourself in three steps
The fastest way to a good result is not to turn all the settings at once. Always change only one variable: first the grind size. Dose, target amount and temperature should remain as consistent as possible during the tests.
1. Start with a sensible base recipe
For a classic double espresso, you can start with 18 grams of coffee grounds in a double basket. The target is around 36 grams of espresso in the cup. This 1:2 ratio is a reliable starting point for many Italian espresso roasts.
The extraction time should be approximately 25 to 30 seconds from the first visible drop. Depending on the machine, bean and desired style, 22 or 32 seconds are also perfectly reasonable. Time is not a law, but it helps you identify the right direction.
A small digital scale makes all the difference. Without it, the grind size becomes guesswork, because you cannot reliably compare your coffee amount or drink volume. For everyday use, a simple model that measures to the gram is sufficient.
2. Watch the shot, not just the clock
Start the shot and watch: After a short pre-infusion phase, the espresso should flow evenly from the portafilter. A steady, continuous stream is a good sign. If the coffee sprays out the side or individual light streams come from different places, the water is flowing unevenly through the puck.
After the shot, weigh the amount in the cup and check the time. Then comes the most important test: taste it. An espresso can still be bitter despite the right number of seconds, and a slightly faster shot can taste excellent. Numbers show you the way, your taste decides.
3. Readjust in small steps
If the espresso flows too quickly and reaches the target amount well before 25 seconds, grind finer. If it flows far too slowly or almost only drips, set it coarser. Always change the grind size by only one small step. With stepless grinders, a few millimeters on the adjustment ring are often enough.
After every change, you should grind out some coffee grounds before making the next shot. This is because ground coffee with the old setting remains in the grinder. Especially with small adjustments, this residue will otherwise distort your result.
With a disc grinder, it is ideally set finer during grinding. This prevents beans from getting jammed between the grinding discs. If in doubt, check your grinder's manual - designs differ.
Interpret the taste correctly: too fine or too coarse?
Sour is not automatically bad. A light, fresh acidity can be intentional with lighter roasts. With a strong Italian espresso, however, you usually expect chocolate, nut, cocoa, roast aromas and a full body. If the coffee tastes unpleasantly sour, green or empty, the extraction was often too short - so the grind size is probably too coarse.
Bitterness is also more nuanced. Pleasant dark chocolate notes suit many South Italian roasts. A fuzzy, drying sensation on the tongue, an ashy aftertaste or unpleasant sharpness rather points to over-extraction. Then the grind size is often too fine.
If the espresso tastes sour and bitter at the same time, so-called channeling may be the cause. The water finds cracks or weak spots in the coffee puck. One part of the coffee grounds is over-extracted, while another part is barely extracted. Then a new grind setting is not necessarily the solution, but rather a cleaner preparation.
Work evenly so the grind size can do its job
Distribute the coffee grounds as evenly as possible in the basket before tamping. Clumps or a slanted puck promote channeling. A simple WDT needle distributor can help with clumpy grounds, but it is not necessary in every kitchen. Most importantly, tamp straight and with consistent pressure.
More force when tamping is no substitute for the wrong grind size. Once the puck is properly compacted, additional pressing has little effect on the flow. Consistency counts: same dose, same basket, same target amount and a clean brew group before every shot.
Also pay attention to the basket. An 18-gram basket does not automatically work well with 15 or 21 grams of coffee. If there is too little coffee in the basket, the puck may have too much room and break more quickly. If it is too full, the puck may touch the shower screen. Stick to the recommended fill amount for your basket first.
Fresh beans change the setting
Very freshly roasted beans still release a lot of carbon dioxide. This can cause them to react erratically during espresso extraction and swell significantly. After the roast date, espresso beans usually need a few days to settle before they flow particularly predictably. Very old beans, on the other hand, lose aroma and crema, even if the grind size is correct.
A new bag almost always requires an adjustment as well. Caffè Borbone, Kimbo, Toraldo or other Italian blends may flow at different speeds with the same grinder setting because the bean blend, roast and density vary. This is not a disadvantage - it is the reason why freshly ground coffee can be adjusted so individually.
Store the beans airtight, cool and dark, but not in the refrigerator. Better yet, only fill the bean container with enough for a few days. This keeps the taste and setting more stable, especially if you do not prepare several espressos every day.
What is different with small grinders and automatic machines
With a portafilter machine and a good espresso grinder, you have the most control. Small blade grinders, on the other hand, are unsuitable for espresso: they produce very uneven particles, making the shot almost impossible to reproduce. For Moka, filter coffee or French press, this may be enough, but for espresso, a proper disc or conical burr grinder is worth it.
The same principle applies to automatic machines, but with less room for adjustment. Only set the grind size gradually and while the grinder is running, as specified by the manufacturer. After that, the machine usually needs two to three shots for the new setting to take full effect. In addition, the selected aroma strength on an automatic machine influences how much coffee is ground per shot.
Anyone who drinks espresso regularly at home or in a small office benefits from a fixed routine. Briefly note down the dose, target amount and grind setting for each favorite bean. This saves time with the next bag and prevents every cup from becoming an experiment again.
When you should not adjust the grind size
A suddenly bad espresso is not always related to the grinder. If the shot sprays unevenly, first check the distribution and tamping. If it generally becomes slower, even though you have changed nothing, a clogged basket, a dirty shower screen or a full grinder outlet may be the cause.
Water and temperature also play a role. Very hard water affects the taste and the machine. If the espresso becomes permanently bitter, especially with dark roasts, even though the time and amount are plausible, it is worth checking the brewing temperature. Not every machine allows you to adjust it - but proper maintenance and regular descaling always remain relevant.
Give each bean two or three careful test shots instead of changing everything after a single attempt. With good, freshly delivered beans and a small note about your setting, the morning espresso will quickly become predictable - and that is exactly when you have more time for what really matters: a really good cup.