Why do different brew devices need different grind sizes?

‘Fancy a brew?’ is a phrase we’ve all heard 100’s of times.

Usually referring to a cup of tea; however, brewing is what we also do to coffee. It’s a hugely important part when making a coffee, and although it seems like we are just adding hot water to ground coffee, it’s a bit more technical than that.

It’s very easy to brew a bad coffee, but by following basic principles and understanding them, you can make the process fun and have great tasting coffee instead.


pulling a double shot of espresso


What is brewing?

Although chocolate covered coffee beans may be a tasty way to get your caffeine fix, it’s not the most efficient. Like tea, we need to add hot water to coffee to extract the flavours that make up our cup of coffee.

Coffee beans are mostly made up of cellulose which is insoluble and why we need to grind the coffee, to get to the parts of the beans that are soluble. If you add hot water to whole beans, nothing will happen for a looooooong time!


coffee in a cooling bin


How to brew

Grinding your coffee is also very important to the outcome of your coffee. Depending on the brew device chosen, you will need a grind to suit. For instance, generally speaking, if your grind is too coarse, you may not be able to extract enough flavour and body from the beans, resulting in a weak, sour tasting coffee, known as under extraction.

If your grinds are too fine for your brew device, on the other hand we have over extraction. Over extraction occurs when the contact between the water and the coffee is too great. This could happen if the coffee is in contact with the water for too long, or the grind size is too fine.

If the grind is too fine, more surface area of the coffee is in contact with the water at any one time, which also leads to over extraction. This, in turn, leads to a bitter taste in the cup.

When brewing coffee, we are looking to find a middle ground between these two. We are hunting for the sweet spot.


holding a red mug


Each different coffee device has a guideline ratio of coffee to water, to determine the strength of the coffee.

In the past, when we talked about strength, it was often misinterpreted to show how dark the coffee is.

For example, a supermarket coffee brand may have medium strength coffee which is shown as a 3 on the bag, or a darker roast may show a 6. This is an incorrect use of strength as it indicates the colour of the roast, not how strong it is. Yes, it may taste more intense as it is a darker roast, but it is not stronger in caffeine. In fact, the lighter the roast, the more caffeine it has as less of the caffeine has been roasted out. There’s one for the pub quiz :-).


coffee in sample trowel from roaster


At Two Chimps Coffee, our hand roasted speciality coffee has been sourced and roasted with different brewing devices in mind. We always have a range of six delicious coffees to choose from, plus two limited editions too.

We roast our coffees not just with the brew device in mind, but the time of day you brew too. For instance, our two coffees for the morning include a darker roasted coffee for that initial boost and a super fruity coffee to start your day with a zing.

Don’t want caffeine in the evening? No problem. Our chemical free decaffeinated coffee  is just the ticket too.


Pouring coffee from a moka pot


When using coffee ratios, our ratios are recommended based on how we like to brew our coffee and to give our customers a guideline to start from; there are no set rules.

For example, a traditional espresso ratio is 1:2; meaning for every 18g of coffee that goes into the portafilter for brewing, we want 36g of liquid in our cup, whereas, for a cafetière, our ratio is 1:20. This amounts to 25g of coffee per 500ml of water, giving us a much weaker brew, 10 times more diluted in fact!

So, you are following a ratio, but it still doesn’t taste right? Ah, that’s the grind size.


A Cafetiere with a swan neck kettle


Let me explain.

In the example of the espresso ratio above, we are looking for 18g in and 36g out. This is a ratio of 1:2. However, there is also another variable to consider. The coffee that comes out needs to come from the portafilter in a particular time frame; usually between 20-26 seconds, depending on your espresso machine.

To change the speed of the extraction, we adjust the grind size. If the grind was very course, the water could pass through it very easily, giving you 36g in just a few seconds. On the other hand, if the grinds were too fine, the water would struggle to pass at all. This could mean that we get 36g eventually, but after 45 seconds or so.

So, even though our ratio is correct, we will still end up with an over extracted or under extracted coffee in the cup.


espresso pouring from an espresso machine



Grind size and pressure

As we mentioned above, grind size plays a key part in making a great coffee taste good or bad. For ease, we have separated the brew methods into two types; gravity and pressure. An example of a gravity method is a V60 filter or cafetière. In both methods, water is added to coffee grounds and gravity takes its course over a longer period of time.

AeroPress and espresso machines are examples of the pressure method where water is forced through coffee and a filter in a much shorter space of time. If you’re forcing water through coffee in only a matter of seconds, you need to make the most of that and extract a good amount of coffee, therefore, the finer the grind, the more coffee surface area there is to extract from.

In a gravity method where your coffee is allowed to brew for minutes, you need a coarser grind as it will spend more time in contact with water and therefore you don’t want as much surface area.


Pouring water into a Chemex coffee maker


Try it.

Have a go using coarse coffee in your espresso machine and a super fine grind coffee in your cafetière. The result is simple; bad tasting coffee. It is, however, a great way to experiment through trial and error to taste the differences between an under extracted coffee that tastes sour and an over extracted coffee that tastes bitter.

When trying to get the grind size right on your espresso machine, it’d always good to start with a coarser grind, this way you know the outcome of the coffee will be sour. From that point onwards you can adjust your grind a little at a time.

By always using the 1:2 ratio, you should be able to notice the slight change in taste each time. It should become less sour until a point where there is hardly any sourness at all, and you get a lovely tasting espresso. If you want to experiment further, then keep going! You’ll eventually start to taste bitter coffee and at that point, you’ll know that your grind has gone too far.


Cup of coffee with a swan neck kettle


Ready to experiment? Grab yourselves some whole bean coffee from our shop now and get grinding.

Want ready ground coffee to take the hassle out? No problem. Find that there too.


Shop now

Join the troop