Dialling In: How Grind Size Affects Coffee

Adjusting and defining a specific grind size is one of the best ways to uniquely tailor the flavour your espresso shots, and get the most out of your coffee beans in general. Different beans require different grind sizes depending on their roast level, freshness and origin to name just a few variables. Its not always easy to know where to begin when you get your freshly roasted coffee beans, so we've put together this helpful guide to give you some pointers to getting that perfect cup of coffee.

What Do We Mean by Grind Size? 

When refer to coffee 'grind size', we are specifically talking about how big or how small the individual coffee grounds are. Why is this important? Well, it is one of the main factors that influence your hot water's the contact time with these particles and how quickly they dissolve compounds from the coffee particles and turn them into a delicious cup of coffee. Finding that sweet spot can be a challenge; grind too fine and you risk over-extracting, grind too coarse and you'll end up with an under-extracted brew. Taking the time to figure out the right grind size is so important to how much you will enjoy your drink. Most baristas, when referring to the size of the coffee grounds, will label 'small' grounds as fine and 'large' grounds as coarse. 

Why Do We Grind Coffee in the first place?

There is nothing better than the smell of freshly ground coffee, but why do we even grind it in the first place? The influence on grind size on the coffee flavour has alot to do with how grinding your coffee beans affects them physically, which in turn impacts our extraction during the brewing process. Grinding coffee into any size will increase the surface area through which your water can interact it. The same coffee bean ground will ultimately contain the same amount of soluble compounds and mass, however the water will have more surface to interact with and extract from; thus producing a much richer and fuller coffee flavour. This is true for different brewing methods, whether you're using the 9Barista espresso machine or a pour-over, and will affect the speed through which water is able to travel through your grounds. Finer coffee will have a slower extraction time, and coarser coffee will be faster. 

Always Grind at Home

When it comes to getting the best out of your coffee, every coffee connoisseur will recommend using recently roasted and freshly ground your beans. But why is pre-ground coffee not ideal for maximising flavour? 

Coffee beans are naturally full of chemical compounds and gases that give your brew its flavours and aromas. When you grind the beans, you increase the surface area which is exposed to the water during the brew process, and thereby increase the extraction of these compounds.

However, as soon as the coffee has been ground it will immediately begin to dissipate some of the chemical compounds into the air, which leads to stale grounds, and a less flavourful espresso. That's why you can almost always taste the difference between coffee grounds bought in the supermarket, and ones you've freshly ground at home. So, what can we do to prevent our coffee from degrading? Unfortunately, there is nothing which will totally stop the gases and compounds from dissipating, but we can slow it down. The most important thing is to buy freshly roasted coffee and to grind the beans just before you use them. Storing ground coffee in a vacuum sealed opaque container will help keep your coffee as fresh as possible too.

Burr Grinders and Blade Grinders

Of course, not all grinders are made equal and its important to understand what to avoid if your keen to get the perfect grind size. In the coffee world, there are two main types of grinders: burr and blade grinders. A blade grinder works in much the same way as a food processor; it will use a spinning blade to speedily chop the coffee beans into small particles. The longer you expose your beans to that blade, the smaller and smaller they will become until they are 'dust-like'.

On the other end of the spectrum, we have burr grinders. Long hailed by coffee enthusiasts, and professionals alike as the better of the two for quality and consistency. Burr grinders work by rotating two ceramic or stainless steel interlocking discs - some are flat, and some are conical depending on the brand - with sharp teeth. The grind size is determined by how close, or far apart these discs are from each other. For an espresso grind, you'd want them to be fairly close to get the fine grounds needed in that particular brew method. 

The main reason most baristas will prefer this grinder over a blade one is down to consistency, both in the shape of the grounds and the size. With a blade grinder, your only real form of control over the end result is time: blend for longer and you'll get a fine grind, blend for shorter and you'll get a coarse grind. Additionally, your coffee beans will not always be exposed to the blade itself, sometimes it will be suspended in the air around the blade or rubbed up against the side of the blender walls, which results in all sorts of weird and wonderful shaped grounds.

A burr grinder, on the other hand, allows you to control the grinding process to a much higher degree of precision. This ultimately means you can achieve a much more consistent grind size and shape as you maximise contact with your grinder and also have complete autonomy on how much or little you want that grinder to interact with your beans. 

However, that's not to say that even if you only use burr grinders, you'll always get a perfect consistency. There will always be some that have ground finer, and some coarser - there will always be some variation to the size and shape of the coffee particles. Higher quality grinders will be able to limit this and will produce a much higher level of consistency, and is probably the single best thing you should invest once you've begun your home espresso journey. 

How To Tell When You've Achieved Your Specific Grind Size 

Knowing about the importance of grind size and its affects on the flavour of your brew is all well and good, but how do we know when we've found the right grind size for our chosen method? Some grinders will helpfully label the appropriate range to use, but not all. So here's a general rule for some brew methods:

• Espresso Makers- This is ground very finely, and is the best grind size to use for the 9Barista Espresso Machine. Brewing in espresso conditions, exposes the grounds to high pressures so we need them to provide resistance or we risk under-extracting and having a very fast shot. By grinding fine (you'll looking for the consistency of table salt), this forces the particles close together and increases the surface area through which the pressurised water interacts with instead of it just shooting through. 
• Pour-over Brewers - This is a (generally speaking) medium grind size - this has the consistency of grains of sugar, however this all depends on how much coffee you're making. If you're making a big batch for your whole team, you'll grind coarser but with a larger dose. Conversely if you're making one just for you, grind finer with a smaller dose. 
• Cold Brew - Since this brew method happens over a long period of time, with a large dose, you would aim to for coarse grounds - these look similar to chopped up chocolate. 

Keep Adjusting, Keep Experimenting 

As with everything relating to flavour, finding the perfect grind size is down to you knowing how you like your coffee to taste. You'll want to, generally speaking, stay within the parameters discussed above, but you'll want to finely tune your grinder to your specific taste. 

The lower the percentage of dissolved compounds in your final cup, the more acidic and sour your brew will be, and the higher the more bitter. So, if you're finding that your espresso is tasting particularly bitter, you know you need to grind coarser on your next extraction. Have fun with it! It can be challenging finding the perfectly balanced cup, but it's worth doing. Of course, its worth stating that every coffee is unique in its own flavours and aromas, even the roast level will impact your final taste and how your grind. 

It can be difficult to know what grinder to go for, so we have already made a helpful list of ones we recommend for the 9Barista on our knowledge base here and we also stock the Knock Aergrind and Commandante C40 on our website. which are great options! 

What are your thoughts? What's your favourite grinder? We'd love to hear from you!