What Impact Does Re-grinding Coffee Grounds Have on Coffee Grinders? What's the Difference Between Electric and Manual Grinders?

The Problem of Coarse Coffee Grind

Friends who often make coffee at home have likely encountered this problem: What should you do when your coffee grounds aren't fine enough? This typically happens when you forget to adjust the grind setting before grinding, resulting in coffee grounds that are too coarse! When the grind size doesn't match the roast level, it can easily lead to extraction inconsistencies. In such situations, you might come up with the unusual idea of "throwing the coffee grounds back into the grinder and grinding them again." So, is this approach actually feasible?

Double Grinding: Is It Viable?

Actually, in past coffee competitions, several competitive baristas have adopted this approach, regrinding coffee grounds to achieve the ideal coffee particles. This operation has been termed "double grinding." Because of its use by competition participants, many people have developed the impression that double grinding is simple to implement. However, when you actually try it, you'll discover it's not simple at all.

The general impression of a grinder is that it breaks large particles into smaller ones. Since coffee beans can be ground from whole large particles into small ones, then coffee grounds that are coarser than the grind setting should naturally be able to be ground to the target particle size. However, many people overlook a crucial point: coffee beans generate many particles smaller than 0.25mm during grinding, which we call "fines." With double grinding, the quantity of these fines will multiply!

A moderate amount of fines can add complexity to coffee and provide a better flavor experience; too many fines can easily clog water channels, leading to over-extraction.

The Issue of "Grind Retention"

Secondly, we should know that most coffee grinders have a characteristic of "grind retention." Because grinders need to leave space for the burrs to rotate, these empty spaces become "safe havens" for coffee grounds. During grinding, some coffee grounds are thrown into these spaces by the centrifugal force generated during rotation, where they're neither ground nor able to exit from the outlet (or due to electrostatic adhesion). This results in the phenomenon where 20g of coffee beans go in but only 19.8g of grounds come out - what we commonly call "grind retention."

Double grinding also increases the static electricity in coffee grounds (due to more friction), and more particles will adhere to spaces unreachable by the burrs due to static electricity. FrontStreet Coffee conducted a special experiment, with results as shown below!

(Coffee grounds adhering inside the grinder) Most coffee grounds adhered to places unreachable by the burrs! After double grinding 19.8g of grounds, only 13.8g came out. That means a full 6g was missing!

Because these 6g of grounds remain in the grinder, you'll need to remove them by disassembling the machine, using compressed air, or grinding new beans to carry them out. This is both time-consuming and laborious. If not cleaned promptly, it can easily cause the burrs to clog or the machine to break down. Or if the next batch of coffee beans is ground without "purging" (using beans to remove the previous grind's coffee grounds), then these 6g of grounds hidden in the burrs will be added to the next batch of coffee grounds.

This situation mainly occurs with electric grinders, while for manual grinders, the impact is not as significant (they're easy to disassemble and clean).

Alternative Solutions to Coarse Grind

So we can learn that for electric grinders, double grinding has quite significant impacts! It produces more fines and increases cleaning time. If you have time to sift out fines and clean the coffee grinder, then double grinding isn't impossible, as it can indeed achieve your desired particle size. But if you don't want to clean, we can try adjusting other parameters to correct the extraction efficiency lost from coarse grinding.

Coarse grinding reduces extraction efficiency, so we can increase extraction efficiency by raising water temperature and extending extraction time. Specific operations could include: increasing hot water temperature by 2-3°C, switching to a dripper with slower water flow (like Kono or cross-star filters), or increasing water agitation during pouring! These parameter changes can help you extract more coffee substances and reduce under-extraction (provided the grind isn't ridiculously coarse)~

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