Many craft-focused espresso bars “only serve double-espressos” or explain that “we pull all of our shots in pairs” when a customer orders a single or triple shot beverage. We essentially keep one double-shot sized extraction recipe dialed in. But why? Are we just being lazy? Not exactly. This is because our focus is to make the espresso taste the very best that we can, and we would have to be constantly adjusting the grind to switch back and forth between recipes of varying size on one espresso grinder.
But what if we had a separate grinder for single shots? It turns out that just like the laws of the universe are altered in sub-atomic particles or when something is traveling close to the speed of light we also start running into special problems in coffee when we reach extremes. Trying to brew a delicious 15 gram single shot from 6 grams of ground coffee will show this.
The diameter of a portafilter’s brew basket doesn’t shrink proportionally with different doses. Even if you have a shallower basket for single shots, the bed of coffee becomes more pancake-shaped, is prone to channeling, and is difficult to hit appropriate shot-times due to drastically decreased resistance. Less coffee is in the way of the water after all. You have trouble hitting that 25 to 30 second benchmark which gives the water enough time to grab all of that flavor and body you want as it passes through the coffee. As a result, single shots are often much lighter bodied and acidic tasting, especially with modern coffee roasts.
We can attempt to grind finer to make up for this quickening effect, but as with everything in life there is a diminishing marginal return on grinding coffee finer for espresso. In fact, a point comes when the coffee is so fine and flour-like that the water can no longer pass through the coffee bed evenly because the spaces between grounds are just too tiny. Once again this “choking” effect causes flavor and body to be left behind.
It’s not that single shots can’t be executed decently every so often, but in a world where pulling a perfect shot can be elusive with even the best conditions, focusing on one recipe that works best sets us up for success!