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Home Brewing Part One: Grind Size

Posted by Eisha Ryden-Hale on

Beginning to brew coffee at home can be a huge step towards ethical coffee consumption. But with this newfound adventure comes industry jargon and nonsense that’s hard to make heads or tails of.  You may have heard of terms like over extracted and under extracted, but what does that actually mean? How do you make coffee taste good? 
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 easiest 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 moves through the grind it will become evenly extracted and then if it keeps going it will become over extracted.
Okay, but how do you tell how extracted the coffee is? That’s easy, you just have to pay attention to your tongue. Under extraction is experienced as sourness. If you’ve ever bitten into a lemon, think of how your face might have scrunched up. Puckers 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 tongue should just 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 the size of your ground coffee, 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, one is filled with sand and the other is filled with rocks. You imagine yourself pouring the same amount of water into each bucket, which bucket empties first? The one with the rocks 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, then 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 is exposed to water, known as “surface area”. The smaller the grind size, the more surface area of the coffee there is to extract from. Having too much surface area exposed will lead to too much coffee being extracted or, over extraction. The opposite happens when your coffee is ground too coarse. So when you make your grind size smaller or larger, you’re impacting the way 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. We hope we can help you get a little closer to making your coffee just the way you like it.