One of our goals at Trade is to empower home brewers to work on your own brewing recipes and have more fun discovering coffee that tastes good to you. Today, we're going over one of the most important and easy-to-adjust brewing method variable: the grind.
To start at square one (or, more aptly, irregularly and inconsistently sized particle one): grind size refers to how big or small the individual coffee grounds are. Grind size is important mostly because it’s one of the main variables that determines how fast your water will dissolve those particles that turn your water brown and make coffee taste like coffee. Usually, instead of “big” and “small” we use the words “coarse” and “fine” to describe the size of grind particles.
Coffee ground surface area
Grind size’s impact has to do with physical processes taking place on a fairly small scale during brewing. When water is trying to get those flavor particles out of an individual coffee ground and into your cup, it can’t just magically teleport to the center of the ground. It has to start from the outside of that coffee particle and wash away those soluble coffee solids first.
So, say you have one coffee particle and you cut it in half. You’re left with the same amount of total coffee, but there’s now a whole lot more surface area from the inside of that particle that the water immediately has access to. The more pieces you divide that coffee particle into, the more surface area will be exposed (while the total mass of coffee stays the same). So in any brew method, finer coffee grounds will extract faster, while coarser coffee grounds extract slower.
Coffee ground resistance
In certain brew methods — specifically ones where water flows vertically, down into and through a bed of coffee — grind size has a secondary effect. If you take two batches of coffee and grind one way finer than the other, the way those coffee particles interlock will be different.
An analogy that doesn’t really come from the real world, but seems to make sense to everyone I’ve ever told it to: imagine you’ve filled one tube with rocks and another with sand. If you try to pour water through the rocks, it will go right through, because there will always be big gaps in between the rocks. The grains of sand, however, will have very tiny gaps between them, and it’ll take a lot more time for the water to get through. The same thing is noticeable when you change the grind size in a pour over or, especially, in espresso. If you grind too fine, not only will it provide more extraction, but it will also slow down your flow and increase your total time (which will also increase extraction).
Grinding coffee at home
Coffee grinders can be divided into two main camps, blade grinders and burr grinders. Blade grinders work like a food processor or blender, using spinning blades to cut the coffee into smaller and smaller particles. The longer the grinder works, the more coffee particles come into contact with the blades and the smaller they get. Burr grinders are basically two interlocking discs (they can be flat or conical), but for the purposes of this explanation they work pretty similarly) that have sharp teeth on them made from materials like ceramic or stainless steel. While grind size on a blade grinder is determined by time, in a burr grinder, the distance between the burrs determines how big your coffee grounds end up.
Coffee is amorphous — it physically just does not break into even particles. So even in a burr grinder some oddly shaped, bigger particles will slip through the burrs, and some small dust-like particles will be created as well. But most of the coffee you grind will be roughly the same size: the size of that gap between the burrs. In a blade grinder, there are going to be way more different-sized particles in that batch of coffee.
Why is grind size consistency so important? Well, as we try to hammer home fairly often, coffee is a very complex substance that has a lot of different flavor compounds. Compare it to something super-simple: table salt. If you add and dissolve salt in a glass of water, that salt is only going to change the flavor of that water in one way: the more salt is dissolved, the saltier that water gets.
Coffee on the other hand, has tastes of sourness, sweetness, and bitterness, not to mention a ton of different aromatic compounds. And those tastes are all extracted from the coffee at different rates (with acidic compounds mostly being easier to extract, and bitter compounds taking a little more effort). So if you have inconsistent coffee grounds, you’ll extract too much bitterness from some of those fine particles and just acidity from some of the coarse ones, making it hard to get a consistent, delicious cup of coffee.
While we heartily recommend burr grinders, that doesn’t mean you can’t take steps to make your blade grinder work for you. Remembering how big the grind size looks is obviously necessary, but note down how long you’re grinding for and the amount of coffee you’re using. Aim for as consistent as possible.
The grind size for every coffee brewing process
Adjusting grind size for specific recipes is part of the fun of brewing at home, but general grind size recommendations do exist — and for good reason. Some grinders have labels on them denoting different brew methods, but if yours doesn’t, here’s a quick guide:
- Turkish coffee gets ground as fine as possible, because those super-fine particles help with the desired body of the coffee, but also because the coffee grounds are only in contact with really hot water for a short part of the brewing time. Those tiny particles are necessary for extraction speed.
- Espresso is ground slightly coarser, but still very finely. Again, we need those fine particles because of the super-short brew time. They’re also very important for providing resistance to the water. Espresso is brewed under high pressure, which increases extraction speed, but without that fine grind enabling us to push those grinds super-close together, the pressurized water would just shoot through coffee bed too quickly for an even espresso.
- For pour over and automatic drip brewers, we tend to grind somewhere in the medium range. Generally, for smaller, single-serve pour overs, we’ll go a little finer. Since we’re using less water, it’s going to be harder to extend the brew time, so the finer grind will help extract quickly. Also, the resistance from the finer coffee grounds will help the water drip more slowly. If you're brewing a gallon and a half of coffee at once (say in a coffee shop), grind closer to medium-coarse, so as not to extract too much or make it too hard for that water to go through.
- For a French press, grind pretty coarsely. While this helps with extraction (resistance isn’t really a concern, because the water’s just sitting there), it’s also largely because the filter of the French press would let too many small particles through if ground finer.
- Cold brew coffee beans are also ground pretty coarsely, both because of its extended brew time and its filtration, which usually isn’t quite as fine as the paper filter in a drip machine.
Adjusting coffee grind size
While you’ll want to stay within these general neighborhoods for grind size, most grinders have plenty of wiggle room to make smaller adjustments. Use those adjustments to help brew coffee that’s not just delicious, but exactly to your taste.
The lower a percentage of the brown stuff in your coffee grounds extracted into your cup, the more acidic your coffee will be. The higher a percentage, the more bitter. So if your pour over tastes too bitter, go a little coarser, repeat all the other steps and it should help. If your French press tastes too sour and is missing a bunch of sweetness, grind a smidge finer and it should taste more balanced.
Every coffee is different, so you’re not going to get a dark-roasted Brazil to taste super-bright just by grinding coarse, and you’re not going to get a flowery washed Ethiopia to taste like a dark chocolate bar by grinding fine. But in highlighting rich, chocolaty Brazilian notes and that Ethiopian's floral flavor, it’s a vital adjustment to understand.