Okay, so grinding. It’s a simple concept, yet still the root cause of bad brews for so many folks making coffee at home (it sometimes befuddles professionals, too, if we’re being honest). Your grind setting is a fundamental variable that can unlock the full potential of your coffee, but it’s a topic that does require a bit of understanding. So let’s get to it!

Consider what would happen if you tossed a roasted coffee bean – wholly intact – into a cup of hot water. Nothing, really, for a while, but eventually the flavoring materials (i.e., chemical compounds) would be released from the bean and dissolved into the water. This is a time-consuming endeavor, and you don’t have to try this for yourself to guess that the resulting beverage would not be ideal. Next, imagine splitting a roasted coffee bean in half. In doing so, you’ve doubled the available surface area and provided a much shorter pathway for water to penetrate the inside of the bean. Don’t brew coffee like this, either, but hey, we’re getting somewhere!

If you continued along this path – splitting the bean segments and exposing more surface area – you’d see the rate at which coffee’s flavoring material is dissolved into water increase dramatically as the particles became smaller (i.e., finer). And at some point, you’d find a nice place where the brew time takes a few minutes and the resulting flavor is complete and balanced.

What’s happening to your coffee as you break down the bean fragments into smaller and smaller pieces is pretty straightforward. 1) Carbon dioxide that’s been trapped inside the coffee is released, which allows easier access for the particles to absorb water; and 2) the increasingly smaller particles create an ever shorter distance that the water must travel to properly extract coffee’s flavoring material.

What happens when the grind is too fine, or coarse?

If we have too much surface area (i.e., the grind is too fine), the water will readily extract chemicals that lead to coffee’s flavor, but it won’t stop there. You see there are other, less desirable chemical compounds that can be pulled into our brew and pollute the flavor. We call this overextraction and it leads to bitter, harsh flavors.

On the other hand, if we have too little surface area (i.e., the grind is too coarse), then our brewing water will have a difficult time reaching and unlocking the flavoring materials inside the coffee fragments. We call this underextraction, and it results in a grassy, sharp brew that lacks sweetness and balance. In this case, we’ve gotten some of what we want from the coffee fragments, but not everything we need.

The relationship between grind and brewing time

Since we know that water can more readily extract flavoring material from smaller particles, it’s intuitive that finer grinds call for faster brew times. (And conversely, coarser grinds need longer brew times.) So when making adjustments to your grind setting, also consider the impact this will have on the time of your total brew cycle.

Particle distribution is a fancy term for “you need a new grinder”

We’re almost home, y’all, but here’s the last tricky little bit. All ground coffee will have a range of particle sizes. Even the best grinders on the market (like the ones we have in the shop) have some amount of smaller and larger particles in addition to the size we’re aiming for. Our goal is to tighten this distribution, so that we maximize the amount of coffee that’s the right size, and limit particles that are either too fine or too coarse.

Alright I saved the bad news for last. That blade grinder – it’s not getting the job done, frankly. Among its many flaws is the massive range of sizes that your coffee particles will fall between. Cheap blade grinders can leave you with too many particles that are excessively fine and excessively coarse, so your resulting whack coffee could be both underextracted and overextracted! For quality results, look for a decent burr grinder. At my home, I use a Baratza Virtuoso, but several less expensive (and more expensive) options are available.

Have a question about coffee or tea? Drop us a line at info@mammothespresso.com.