While these guides offer a helpful place to begin, there’s a number of factors that they don’t consider. Coffees of different roast levels, density, and freshness all perform best at more nuanced grind sizes unique to themselves. As a home brewer, it’s both fun and empowering to know how to make small grinder adjustments to optimize a coffee’s flavor to your preferences.
Many baristas refer to this nuanced flavor optimization as “dialing in” a coffee. Generally, this entails making small adjustments to the grinder and brewing ratio of coffee to water. Both factors ultimately affect the “extraction level” of a brewed coffee or the amount of soluble coffee particles taken from the grounds into the brewed coffee. Extraction level can lead to drastically different flavors of brewed coffee.
Broadly speaking, a finer grind size will typically yield higher levels of extraction and a more coarse grind will yield lower levels. This is because coffee which is more finely ground has increased exposed surface area on each tiny particle of coffee. It’s also harder for water to flow through a finely ground bed of coffee, which increases water’s contact time with the coffee.
So, how does this all relate to a home coffee brewer? Having this knowledge in your back pocket can help you make the necessary adjustments to brew your perfect cup at home. Coffees brewed with too fine of a grind size will taste more bitter, harsh, and heavy and will have muddled flavors. On the flip side, too coarse of a grind will yield sour, weak, and dry flavors. If you run into any of these negative flavors in your cup, make a note to take your grind a couple of notches finer or coarser for your next brew, depending on what you’re tasting.