You got your coffee but it’s way too coarse for what you want to do with it. What are the problems you could run into and what can you do to make it better?
Coffee beans should be ground to the correct size for a specific brew method. If the grounds are too coarse for a certain brew method, the resulting coffee will likely be sour and/or weak. Coarse grounds don’t have enough surface area to extract fast enough and let water through the bed too easily.
Why is that the case and is there anything you can do about this? Let’s find out.
What Happens If Coffee Is Ground Too Coarse
What exactly is too coarse depends on your brew method, specific beans, and your personal taste. Keeping that in mind, there are three main issues you’ll run into if the grind size is too coarse.
1. Sour tasting coffee
Taste-wise, you’ll get a sour cup of coffee from grounds that are too coarse for your purposes. To understand why this happens, it’s important to understand extraction. There are many different compounds in a coffee bean. They are solid in the bean but they can be dissolved in water. Getting those compounds from the grounds into the water is what brewing coffee is. Dissolving those compounds is called extraction.
Those compounds dissolve into the water at different rates (and at different temperatures). The ones that are dissolved the easiest, taste very sour. You want to extract the right amount from the grounds to balance out the taste. The really harsh bitter-tasting ones come out last.
Now here’s where grind size comes in. If the grounds are too coarse for your brewing method, there is less surface area than ideal. That means the water can touch less of the grounds at the same time which leads to less extraction being done in the same amount of time. That leads to lower extraction and likely a sour cup of coffee.
2. Flow problems
If the grounds are too coarse, you can have some issues with how fast your coffee flows through your filter. The coarse particles mean that there are bigger channels between them. Think about sand. There is not much room between the grains of sand. Now take a bucket of random rocks. There are much bigger gaps between them.
That means that the water flows through the bed of coffee faster than it should. This compounds the extraction problem. Not only is there less surface area for the water to act on, there is also less contact time so the water that is there has less time to do the extraction. So grinding coarse will produce sour but also weak coffee.
As a side note: This is why immersion brewing methods can/have to use a coarser grind. With immersion brews like a French press, the water and the grounds hang out for a while together. This gives the water more time to extract the grounds.
3. Wide grind distribution
This one depends on how coarse you actually grind the coffee, not just if it’s too coarse for your brewing method.
The coarser you set the grinder, the wider the range of particle size that will come out of the grinder. A burr grinder sets the grind size by changing the distance between the burrs. If the burrs are closer together, the smaller the piece of coffee has to be to get through.
Now when you grind coffee, the beans break up more than they are cut. Just like when you break a cookie, you get two pieces but you also get a lot of smaller pieces. The same thing happens with a coffee bean. So you get those tiny pieces and if the grinder is set coarse, those tiny pieces just go straight through because they’re already smaller than the size the grinder is set to.
This means you get the bigger pieces but also a lot of the smaller pieces. This means you have a wide range of particle sizes. So some will be too small for your brewing method which leads to a bitter coffee because those small particles get extracted too much. It can also cause problems with your filter and clog it up.
How to adjust your coffee grind size
If you grind your own coffee you probably use a coffee grinder for this and don’t do it by smashing the beans with a hammer. Most coffee grinders can be adjusted so the grinds that come out are roughly a certain size.
There are two exceptions that can’t be adjusted:
Pretty much every other grinder is adjustable. The size of the grounds that come out of the grinder is adjusted by changing the distance the burrs are away from each other. How to adjust them is different on every model. Usually, there will be something you can turn. On most electric grinders there is a pretty big knob you can turn. On other models, you can turn the whole hopper.
On hand grinders, the size is usually adjusted either on the bottom or by removing the crank handle and adjusting it from the top. On most hand grinders it’s a little more difficult than on electric grinders.
What to do with coarsely ground coffee?
Maybe you have the coarsely ground coffee and don’t have a grinder or don’t want to grind it again. What can you do with it?
Check how coarse it actually is and which brew method might be suitable for it. For example, coffee that’s significantly too coarse for an espresso machine might work well for a pour-over. And coffee that’s too coarse for a pour-over can be used in a French press. And if it’s really coarse, you can always make cold brew.
You can always find a use for coffee grounds even if it’s not exactly what you need or want. Even if it would be completely unsuitable for brewing coffee, you can still use it to make a coffee scrub or heavy-duty soap.
If you made a mistake and you have really coarse coffee, can’t you just run it through the grinder again?
You can make it work but only if the difference is really big. To go from medium to medium-fine is not going to give any workable results. You’ll create a lot of fines that either clog up your filter and/or make the coffee very bitter.
With really big differences it can be worth a shot. You’ll have to figure out what works for your grinder. It’s unlikely you’ll get great results on the first try so there will be some coffee wasted.