In conversations with baristas about espresso, one of the things they always seem to be talking about is “dialing it in.” As an expression, the phrase means that they want to make the espresso great. In practice, it means that they are adjusting their equipment to make sure that you get the right combination of grind (particle size) and dose (amount) of coffee. Literally, it involves moving the dial on the grinder towards coarser or finer.
If you stop in at your favorite specialty coffee shop and watch the baristas during a busy period, you will probably notice that they keep filling up the hoppers on top of the grinders, without letting the amount of beans get too low down the sides. A barista at one of my regular coffices explained to me why doing this is so important.
As the weight of the beans pressing down toward the burrs of the grinder changes, so does the grind. When the beans get lighter, the pressure they exert is lower and the grind becomes coarser, so you have to turn down the dial on the grinder. Conversely, if you have a grinder adjusted properly for a hopper with few beans in it and then fill up the hopper, you need to open up the burs a little to compensate for the extra weight. Maintaining a constant level in the hopper helps the barista make consistent shots without having to adjust the grinder each time.
Keeping the hoppers filled is not the only thing the baristas must watch. When the ambient temperature and humidity rise or fall during the day, the grind changes too. According to another barista, some days the beans just do not want to cooperate, as if they had their own personality. Regardless of what causes the changes, baristas must watch the grind very closely to make sure that their shots stay consistent. They measure the consistency by watching the flow of espresso as it pours out of the machine, by measuring how long the shot takes to pull and also by tasting the occasional shot.
As baristas gain experience, they learn to instinctively adjust their equipment to accommodate changes in the beans and the grind. They start making more consistent shots and drinks and they can do it more quickly. As a customer, you might not be aware of the little details that go into making your drink, but you don’t need to be, because your barista takes care to “dial it in” for you.