Beginning to brew coffee at home can be a massive step towards ethical coffee consumption. But with this newfound adventure comes industry jargon and nonsense of which it's hard to make heads or tails. You may have heard of terms like over-extracted and under-extracted, but what does that mean? How do you make coffee taste delicious?
There are three key variables to control, and they all influence each other and the outcome of your brew. Today, we're discussing grind size and its effect on flow rate and extraction. We'll cover the other two soon.
If you've started grinding your beans at home, this post is for you. And lucky for you, you're already holding the solution to better-tasting coffee in your mouth.
Extraction is simply the flavours you're pulling out of the coffee. I find it most straightforward to think of extraction as a spectrum. When you add water to your grinds, you start at the under-extracted end. As time passes and the water passes through, it will become evenly extracted. Then if it keeps going, it will eventually become over-extracted.
Okay, but how do you tell how extracted the coffee is? By paying attention to what you're tasting. Under extraction is experienced as sourness. If you've ever bitten into a lemon, think of how your face might have scrunched up. oaPuckers even. Your tongue moves into the back of your mouth to try and get away from the sourness.
And bitterness? The exact opposite. It's like when you're 8 years old, and you put pure vanilla essence on your sundae, accidentally ruining the whole thing (or was that just me?). Or when you eat unsweetened cocoa powder. It's dry, and your tongue tries to shoot out of your mouth. When you're in the sweet spot, your pallet should tell your brain "yum", or in industry terms: it should feel clean with a balanced sensation across your tongue. So now you get what over and under extraction is, but how do you fix the extraction?
One way is to adjust your ground coffee size, otherwise known as "grind size". The size of your grind directly affects how fast the water passes through the wet coffee grounds (otherwise known as a "slurry"). Think of two buckets with holes in the bottom, the first is full of sand, and the second is full of rocks. You imagine yourself pouring the same amount of water into each bucket, which bucket empties first? The second one, because there are lots of gaps for the water to get through. If your coffee is under-extracted, this could be because the water is moving through the coffee too fast. So you make the grind smaller, and the water will pass through more slowly, giving it a better chance to extract more flavour. If your coffee is tasting over-extracted, you make the grind coarser like the rocks to create more space.
Grind size not only affects how quickly the water passes through the coffee but also changes how much of the coffee exposes itself to water, known as "surface area". The smaller the grind size, the water has a greater surface area from which to extract flavour from the grinds. Having too much surface area exposed will lead to over-extraction. The opposite happens when you grind your coffee overly course. The way you grind your coffee will affect how your coffee extracts in multiple ways, so remember these changes won't need to be too big - it's best to do a little change at a time.
At Timely, our goal is to give you the tools to make your coffee, just the way you like it. We're not here to tell you exactly how you should brew your coffee, or how it should taste. But we hope we can help you get a little closer to making your coffee just the way you like it.