Disclaimer! This article might get a little nerdy!
Let us talk about a few things- Contact time, Extraction rate, Surface area and Flow rate.
- Contact time- is the amount of time coffee and water sit together.
- Extraction- the amount of coffee taken by the water.
- Surface area- talks about the surface area of coffee. The finer the coffee grinds are, the larger is the surface area.
- Flow rate- the speed at which water passes through the coffee.
- The Surface area- If you divide a coffee bean into two parts, you have the same amount of coffee you had earlier. Still, now there's more area accessible for the water to 'touch'. The more you grind the coffee, the surface area increases, which gives more area for the water to pass through.
- Contact time- Let's take an example of stones and sand. If you pour water over stones, then the water will pass quickly from its surface and drip faster. Now, if you pour water over sand, water will pass through all the granules, taking more time to pass through it, thus reducing the flow rate of water. So in terms of coffee, Finer the grind, more surface area, and thus increasing contact time.
- Extraction- talks about the amount of coffee absorbed by the water in a cup of coffee. If you take the above stone and sand example, you will see that the water collected will be very different from each other. The cup below the sand, will be darker as it has been steeped for longer, and the water has extracted more from the sand than the stone. So the finer the grind, more the Extraction.
Summary
Finer the grind ”> Larger the Surface area”> increased Contact time ”> reduced flow rate”> higher the Extraction.
Coarser the grind ”> smaller the Surface area”> less Contact time ”> increased flow rate ”> lower the Extraction.
Brewing
What coffee grind size you require for your brewing equipment?
If your equipment requires more contact time or steeping, make the grind coarser. ( French Press)
Why? - if the grind is fine, then the Extraction will be high, which will make the coffee over-extracted which will taste bitter.
If your equipment requires less contact time, then make the grind finer. (Espresso)
Why? As the contact time is low, you want more Extraction. If you make the grind coarse, then the Extraction will be low, and thus the coffee will be under-extracted and will taste a bit weak and watery.
What grind sizes for which equipment?
Turkish Coffee- Requires extra fine grind, which resembles powdered sugar or flour. As the coffee is in contact with hot water for a very short time, and to get the desired body.
Espresso - requires a fine grind, which is finer than table salt. As espresso is brewed under high pressure, you want a fine grind to create some resistance, or else the water would just speed through the coffee, which would make it weak. A finer grind is also required because of the short brew time.
AeroPress- A medium-fine grind, resembling table salt. As it is a full immersion method, where the coffee grounds and water sit together for a bit( 1-2 minutes), which increases the contact time. If you want to increase the grind size, you must increase the steeping time to about 3- 4 minutes.
Pour-over / Automatic drip brewers- For single-serve pour-overs, i.e. to make one cup of coffee, use medium grind resembling regular sand. As the water passes through the coffee bed, with very little contact time, the fine grind will help in quicker Extraction. If you want to brew, multiple cups increase the grind size, so as not to over-extract the coffee.
Chemex- Medium coarse grind like coarse sand. Chemex makes multiple cups of coffee at a time, so it requires this grind size. If it is finer, it will over-extract the coffee, making it bitter.
French press- Coarse grind, resembling sea salt. The real reason for this grind is because you do not want want to let the coffee grinds pass through the filter. To compensate the coarse grind, you must increase the contact time to about 4 minutes at least, before you press the plunger down.
Cold Brew- The grind shall be coarse like peppercorns. Cold brew is brewed with room temperature or cold water which does not let the coffee to infuse quickly. The extraction rate is very slow, so to compensate we increase the brew time immensely to about 16 - 18 hours. Even if the coffee was finely ground, it would take a long time, but the brew would be more extracted, making the cold brew bitter. The other reason for the extra coarse grind is to make the filtering easier.
So, does coffee grind size, really matter? Yes. In coffee, the "finest" of the things matter, to brew a great cup!
We hope this article made sense, and you learnt something!
P.S. try to freshly grind the coffee to get better results!
