Why Do Manual Grinders Produce More Fines Than Electric Grinders?

When coffee beans are ground into powder, whether using a high-quality grinder worth tens of thousands of dollars or an entry-level grinder costing just a hundred dollars, the presence of fine particles is currently unavoidable. However, the amount of fine particles can affect our brewing process, making it inconsistent. The choice of grinder can, to some extent, reduce our concerns about fine particles. On this basis, FrontStreet Coffee will compare the differences between electric grinders and manual grinders in producing fine particles, helping everyone understand their differences in grinding functionality.

Grinder Mechanisms

Typically, manual coffee grinders commonly found on the market use conical burrs, while electric grinders mostly use ghost tooth or flat burrs. Therefore, FrontStreet Coffee will compare fine particles between a manual grinder with conical burrs and an electric grinder with flat burrs.

Testing Method

We used both a manual grinder and an electric grinder to grind 10 grams of beans (testing with dark-roasted Golden Mandheling), both set to a grind size that would allow 80% of particles to pass through a Chinese standard #20 sieve. The ground beans were placed in a sieve, gently shaken, and finally, the extremely fine particles were weighed for comparison.

Test Results

Manual grinder: 1.6g of extremely fine particles

Flat burr electric grinder: 0.9g of extremely fine particles

Therefore, when the same coffee beans are ground to the same grind size, manual grinders indeed produce more fine particles than electric grinders.

This is due to the design of the grinding burrs. Conical burrs typically consist of a ring-shaped stationary burr and a cone-shaped rotating burr. The diameter of the conical burr becomes progressively narrower from top to bottom, which affects uniformity to some extent and also更容易产生极细粉更容易产生极细粉.

On the other hand, electric flat burr grinders have a structure where two burrs are placed parallel to each other - one fixed to the machine body and one rotating with the motor. Coffee beans are ground into powder by centrifugal force and expelled from the gap between the burrs. The time coffee beans spend being crushed is shorter than with conical burrs, resulting in relatively fewer fine particles. Additionally, with the assistance of a motor, human error is reduced, and coffee beans are ground at the same speed, which means more uniform grinding results.

Practical Tips

So, if you find that your grinder produces too many fine particles, you can take an extra step: sift out the fine particles. Then, add back a portion of the sifted fine particles, which reduces the amount of fine particles while preserving their flavor.

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