How Grind Size Affects Coffee

- From Finer To Coarser Grinds -

Published: May 31, 2019 · Modified: Oct 11, 2020 by CoffeeAndTeaCorner ·

Wondering why you've got to grind your coffee to a specific size each time? Or maybe you wonder why some coffee packs claim they're best used for Moka coffee or espresso?

That's because of how the grind size of your coffee affects the taste of the final brew.

So how does grind size affect coffee?

In short, the surface area of the coffee bean dictates the extraction time. This means that a very finely ground coffee bean, like for espresso, will brew quickly, in under a minute.

And a coarse ground, like for the French press, will mean a longer brewing time. But also a more flavorful cup of coffee.

Like with tea, the smaller the surface area the easier it becomes for the flavor to go off and end up too bitter or acidic. Most often, you end up with a better cup of coffee if you use a coarser ground coffee with a longer brewing time.

This is because a coarse grind offers a more 'complete' flavor, as the steeping time is just right for that. Let me explain a bit about the surface area first.

If you want to make the best coffee at home, you absolutely need to check my article on the best coffee gear.

The surface area of the coffee dictates the brewing time:

So what would happen if you just threw in hot water the whole coffee bean and expected it to brew?

You'd be waiting for a long, long time. About as much as for a cold brew.

This is because the larger the surface area, the more time water needs to effectively extract everything from the coffee bean.

This means that different grind sizes will bring you different coffee types. Some will be done very quickly, like an espresso that uses the finest grind possible.

And there's also the fact that water's meant to pass through those grounds, and in some cases, it needs very little resistance.

Smaller grinds allow faster extraction time:

If you use a smaller ground, like for a drip filter, you're going to see individual bits of coffee, just a bit smaller than poppy seeds.

This means that there's less surface area for the water to cover and extract, which means you can use a fast extraction method.

It could be a Turkish coffee, it could be espresso, it could be Moka.

You could even use a smaller grind than that, as fine as you can get it.

This will serve to brew the coffee very fast, but in some cases provide the right resistance for water to pass.

For example in espresso, a very fine ground is welcome, as it will slow down a bit the speed at which the hot water comes through the metal filter. This allows for a few extra seconds of brewing time.

If you were to use coarser grounds, like medium, for a shot of espresso, you'd be left with a watery mess that's not really coffee at all.

Small grinds also require a lower water temperature, so you don't risk over-extracting it.

You might wonder if espresso is over-extracted. It isn't, because the show is pulled in only half a minute. The coffee won't over-extract in such a short time, but it will if you let the shot run for a full minute.

Do finer grounds make stronger coffee?

No, not necessarily. Finely ground coffee, so the finest of them all is usually used for espresso, at least in the West. Further east it's also used for Turkish coffee.

But an espresso isn't exactly stronger than other coffee types, like filter coffee for example.

However, it might taste like it's stronger, harsher, and more bitter because it's a very concentrated form of coffee. After all, it uses 7 gr of ground coffee per 1 oz/33 ml of brew (1 standard shot of espresso).

So in short, no. Finer grounds do not make a coffee stronger, but they do brew much faster than other sizes.

Larger grinds (coarse) are better for long steeps:

Alright, so what are coarse grounds good for?

For example, coarse-ground coffee is great for French press, cold brewing, and cowboy coffee as well.

If you're confused about what cowboy coffee is, it's another way of making coffee in a pot.

This is because each of these methods uses a longer steep time, and as such, they can handle a larger surface area.

Or maybe the surface is dictated by the steep time, and that's how the long steep time methods came to be?

Was it the egg or the chicken?

Who knows, the point is that large grinds need longer steeping.

As such, this also means that the water can pass freely through all that ground coffee. For example in a french press, a coarse grind makes is trapped by the mesh filter and your coffee won't have actual grit in it when you pour it.

However, it will have more body to it, as you've let it steep for a longer time.

And a longer steep time offers a better, more nuanced flavor. This is because the coffee releases its flavor as it needs to, and isn't rushed in any way. Looking at you, espresso.

About over-extraction and under-extraction in coffee:

This is an important point to understand since it will make the difference between good and bad coffee.

An over-extracted coffee is one that has more elements extracted than it needs. Out of a coffee bean, only about 30% of the nutrients and flavor can be extracted.

But the optimal amount is 18-22%. Anything over that and the coffee becomes too bitter, too sour/acidic, and just bad in general.

Underextracted coffee is less than 10% of what it can extract. So it's a weak cup of coffee, with barely any 'body' at all and the flavor tastes a little flat.

So how do you avoid this?

You take care to brew the right-sized grind at the right water temperature, and for the right amount of time.

So for example with small grind sizes, you will not let them steep for 4 minutes. And you will not brew it at 212 F/100 C, as it's much too harsh. In fact, no coffee needs to be brewed at such a high temperature.

The most you should be brewing small-grind coffee at is 93 C/200 F.

A good brew time for fine-grind coffee is 1-2 minutes, like espresso and Turkish coffee.

As for coarser grinds, you will need to up the steep time to 4 minutes (max), for brews like a French press. The water temp should be 93 C/200 F, and allow the coffee to brew at its own pace.

Leaving it to brew for only 2 minutes would be much too little, and you'd get a weak cup of coffee. Let it brew for 7 minutes, and your coffee will taste 'burnt', and not of any specific flavor.

Why there are different grind sizes in the first place:

The grinder you use to grind the beans at home matters very much.

To be more specific, the way the grinder works matters. It can be either a blade or burr grinder.

If it has a pair (or more) of blades, it will cup up the coffee beans, and not offer a very coherent kind of grind. Some bits will be smaller, some will be larger. You have to keep twisting and shaking the coffee grinder, until all the bits a cup up.

Unfortunately, this often results in bits too fine, and bits too large. You might end up giving up and just going for a very fine grind, just to be sure your grind is even enough.

Burr grinders are going to force the coffee beans into the same, even, amount of space. So no bean can be larger than the size you set, and they will all be ground into an equal and constant amount of space.

This leaves you with the most uniform grind size possible.

Of course, these grinders are usually more expensive, but well worth the price given the quality.

Final thoughts:

In conclusion, it does matter what size coffee grounds you use, so that you may brew coffee the right way.

This means that if a pack of coffee says it's ground for Moka pots, then it's going to be a smaller grind, possibly medium-small. It would also be good for a filter coffee, either pour-over or drip.

Of course, grinding your own coffee makes it possible for you to always have the right grind size for whatever coffee you want to make.