Grinding quality is related to the particle size distribution of the ground coffee powder, which can be simply defined as: a grind with a more concentrated particle size distribution is a higher quality grind.

A more concentrated particle distribution means less coarse and finer particles are produced during grinding. Ultrafine powder is an important factor affecting the extraction flow rate. Reducing the ultrafine powder can make the extraction water flow through the powder layer more smoothly and the extraction flow rate will be accelerated.

In the parameter design of the same extraction time and extraction volume, the particle size distribution is more concentrated, which allows us to choose a finer grinding degree, increase the total extraction surface area of the coffee powder, and achieve the goal of increasing the extraction rate. Of course, this isn’t the only way a high-quality grind can increase your coffee extraction rate.

Highest extraction rate dominated by “tannins”

Whether a cup of espresso is over-extracted cannot be simply defined by a number, but by whether tannins are extracted during brewing. Or whether we drink the bitter flavor brought by tannins from coffee.

Tannins, also known as tannins, are found in the structural fibers of coffee beans. As a large molecular weight substance, it is a water-soluble compound that is extracted in the final stage of brewing.

But the biggest problem with coffee extraction is “uniformity”. In the powder layer, it is never possible to maintain a consistent extraction progress in every area, or in other words, every coffee powder. When a portion of the dissolved substances in the cells of the coffee grounds have been fully extracted, the water will turn to start dissolving the tannins in the wood fibers, and the extraction must stop at this point. Even at this time, another part of the coffee powder with a slower extraction progress has not yet fully released the compounds.

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We can understand that the level of coffee extraction rate is actually determined by the part of the coffee powder that is extracted the fastest, because this part of the coffee powder determines the time point when the extraction must be terminated.

In other words, if you can improve the consistency of the extraction progress of all the coffee powders in the powder layer, make the faster part of the extraction slower, and make the slower part of the extraction faster, then the goal of increasing the highest extraction rate can be achieved.