The ideal coffee grinder produces ground particles that are consistent and of the correct size. By that, we mean that the coffee's ground particle size should match the coarseness setting of its grinder, whether it's fine or not. The size of the precipitate produced should also be appropriate for the intended method of preparation, as indicated in the product instructions.
To test each grinder for our coffee grinder reviews, we first hand wash and dry all parts as recommended by the manufacturer. We then set each machine to the appropriate level for drip coffee grinding or automatic coffee production (again, as specified in the manual). Sometimes the manual lacks specific directions. In this case, we choose the medium coarse coffee grind setting and then increase it by another coarse level (from a fine grind, such as an espresso grind, to a coarse grind). For example, if a grinder has a total of 16 coarse grind settings (assuming 16 is its coarsest grind option and 1 is fine), we'll set it to coarse level 9.
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Next, we measure 10 grams of whole coffee beans for grinding. By default, our test beans are Kirkland Columbian Roasting. These are the same beans we use for our coffee maker tests. (No judgment, please.) When you grind as much coffee and espresso as we do, it pays to be thrifty.
We then run our sample of beans through the grinder. We also note how long the grinder takes to grind coffee beans. Next, we carefully collect the base, then sift it with a sieve with two screens for 60 seconds. That's what we use it for Kruve Sifter System. Our original Kruve Two unit came with two mesh screens of different aperture sizes (800 and 400 microns). This step allows us to measure the grind size and grind consistency of our sample. On Screw base it has now replaced the Kruve Two and offers five mesh screens (300, 500, 800, 1,100 and 1,400 microns).
We used a Kruve Coffee Sieve System to verify grind size consistency.
A superior electric coffee grinder or manual grinder will produce grounds, preferably with stainless steel blades, that are mostly between 400 and 800 microns in particle size (at our selected grind settings). Finally, we measure the base that gathers between the two screens (800 microns top, 400 microns bottom).
A bad grinder will grind particles of different sizes, from large to small. Blade grinders are notorious for this issue. Unlike a bladed coffee grinder, a coffee grinder with steel or ceramic burrs usually produces grounds that are much more uniform in grind size.
Additionally, grind at least two more times. Hence, we can note the average optimal yield for each mill.