When you enter a coffee bar, your eye as a coffee lover often goes first to the large espresso machine. Is understandable. After all, it is the heart of the coffee bar and the workhorse of the barista. Such an espresso machine also often looks beautiful. The small grinder next to it are therefore sometimes overlooked. Too bad, because their role is at least as important as that of the espresso machine. A brief introduction to the coffee grinder.
It's hard to talk about coffee grinders and not mention the burrs. This is the place where the magic happens. In principle, you can distinguish 2 types of grinding burrs. The first type are conical burrs. With this type of grinding discs you have an outer grinding disc and an inner one. 1 of the 2 (usually the outer one) remains stationary when the inner one rotates. The coffee beans fall from above between the 2 discs and are discharged downwards. The 2nd type are flat burrs. These are 2 discs that sit on top of each other. The closer the discs are together, the finer the coffee is ground. Although conical discs are becoming more popular, especially with coffee grinders for home use, it is mainly flat discs that are most often used in a professional setting. Because of the popularity of flat burrs, more is known about them than about conical burrs.
In addition to the type, there are also different types of material that grinding discs can consist of. Most standard burrs are made of hardened steel. Some discs have an extra hard coating that makes them last a lot longer. However, in terms of their grinding quality, it does not matter much what material they are made of.
Uniformity and fines
When you grind coffee, you naturally want all the grains to be the same size. The more uniform the grain size, the better. This applies to both filter coffee and espresso. Good, sharp burrs are the only way to guarantee this uniformity. When the grinding discs become less sharp, the grains will become smaller and less uniform in size.
With espresso, however, there is something else involved; fines. These very small grains play an important role in terms of taste in espresso because of their larger contact surface. In addition, they are also important for controlling the shot time of the espresso. For espresso you like a certain amount of fines (preferably not for filter coffee). Flat burrs with smaller teeth on the ends and fewer grooves on the inside are optimal for making these fines. Due to the lack of grooves on the inside, the coffee beans are transported faster in larger pieces to the ends of the burrs. As a result, they cram visibility on the outside, so to speak, and are more "crushed" than ground. This crushing creates these fines, small crumbled pieces. The same story applies to the rim of the burrs. When it contains less sharp edges, the grains are "squashed" a little more at the end than ground, which again provides more fines. Too much of these fines is also not a good idea. After all, these can prevent or even block the water flow in certain places.
The coffee grinders themselves can also be equipped with all kinds of bells and whistles. Most professional grinders are equipped with a ventilation system that cools the grinding discs during very busy service times. Grinding discs that are too hot have a major impact on the development of fines, which would require the barista to make far too many adjustments to the grinder. You can also adjust the rotation speed on some grinders to control the amount of fines even better. Finally, the latest hype in espresso land is coffee grinders that grind by weight. You set your desired weight and boom, the grinder always gives the desired weight with the help of built-in scales. Very handy for quickly and efficiently adjusting a grinder.