All burr grinders have two burrs. One burr is on a threaded carrier that screws into the grinder body, and the other is attached to the motor. When the grinder is turned on, the burrs tear the coffee beans into progressively smaller fragments as they move through. The grinds exit the burrs as a fine powder and are pushed by a rotating paddle through a chute and into the doser.
To adjust the grinder, the burrs are moved closer together or further apart.
The grind becomes coarser when the burrs are further apart, and finer when the burrs are closer together.
The adjustment is made by way of rotating the collar at the top of the grinder, or less commonly, turning a knob on the side of the grinder body. Usually there is a locking mechanism that must be undone before the grind can be changed. This must be undone before a grind adjustment is made and done up after. If the grinder is left unlocked, the grind setting may adjust by itself.
The size of the grind determines how fast or slow the extraction occurs:
If the grind is very fine, the water passes through slowly. Fine = Slow
If the grind is very coarse, the water passes through faster. Coarse = Fast
Coffee beans behave differently day to day according to many factors, including age since roast, storage conditions, grinder usage, grinder blade condition. The grind size is not ‘set and forget’, and the barista must watch the shot times closely to maintain the recipe.
To achieve the desired yield in the desired time, adjustments need to be made to the grind size. Adjusting the grinder is not difficult, provided you are careful, thoughtful and take your time. You should expect to make small changes your grinder settings several times per day.