Have you ever wondered why different grinders are advertised as “for espresso” or “for pour over”? Or why it even matters to change the setting on your grinder from coffee to coffee? We’re here to help! We’ve got an easy explanation of grind size for everyone just getting into brewing coffee at home.

What is Extraction?

When we talk about getting good extraction, what do we mean? Well, brewing coffee is a chemical process. Hot water molecules bond to particles in the coffee grounds to create brewed coffee. This process is dependent on two main factors - time and heat. Pressure is important for brewing espresso as well, but in general if you have hotter water you need less extraction time. This doesn’t mean you should boil your water for a quick cup, as you really want to match your ideal extraction time to match your temperature, and overly hot water will scorch the grounds and lead to over-extraction. On the flip side, water that’s too cool can cause under-extraction, resulting in a sour cup. This means that really you want to keep your brew temps in the 195-205f range. So where does grind size come in?

 

Grind Size and Extraction

The key thing to consider with the grind size of your grounds is surface area. If you’re brewing cold brew, you want larger grounds. This is to provide more surface area for the water molecules to bind with the grounds during prolonged extraction in cool water. For a press, you’ll use grounds that are a bit finer to prevent over-extraction since you are brewing with much hotter water. You’ll balance this with extraction time to create a bold, but not too bitter brew.

Then there’s the other piece of the grind size surface area puzzle - flow. When you move away from immersion brewing and into drip, pour over, and espresso, flow rate becomes a factor. You need finer grounds to sort of “clog up” your filter and prevent water from running right through the grounds and failing to achieve extraction. For espresso, you’ll want extra fine grounds to create a tightly packed puck that provides backpressure to the water being pumped through the portafilter. We know this might be confusing, but those chemical properties still apply. What we are aiming for is the perfect combination of extraction time and temperature. When the water is passing through the grounds, we use grind size to control that extraction time.

The Devil’s in the Details

The trickiest part of all of this is the details. Different coffees have different flavor profiles that are best brought out by specific combinations of brew parameters. This is why some beans brew better as a cold brew, and some are best as an espresso. This also means that each coffee has an ideal grind setting for each brew method. So how do you find this? And why is it that some grinders just don’t work for certain brew methods?

Well, in order to produce a fine enough grind for espresso, you need tight enough burrs and the ability to adjust them precisely. This requires engineering that is typically more expensive than the most basic entry level grinders offer. As grinder technology advances, the cost of espresso grinders is certainly coming down, but regardless of brew method you still need a good quality grinder to make great coffee. This is because all brew methods require consistency and quality in coffee grounds. So how do you manage adjustments once you have the right grinder?

Dialing In

Regardless of brew method, coffee enthusiasts usually use the term “dialing in” to refer to finding the right grind for a given coffee. For slow brew methods, this process is usually relatively simple. As you increase grind size, the band of sizes that the coffee will taste good in generally increases. This means that you can usually just go with a pour over setting on your grinder for most coffees that you brew with pour over. For espresso, you’ll probably need to pull a shot or two (or three, or four) and make small adjustments in order to find the right grind. In both cases, there is a method you can follow.

As mentioned above, over-extraction leads to a bitter tasting coffee, and under-extraction leads to a sour tasting coffee. This is true regardless of brew method, but most extreme with espresso. So, if your coffee tastes bitter, you want to go with a coarser grind to allow faster flow of water through the grounds, and less extraction time. If your coffee tastes sour, you’ll want a finer grind to restrict flow and increase extraction time. It’s really that easy! You’ll develop a feel for the right time per brew method and the right coffee. For drip and pour over, the draw time for the water through the coffee can take a couple of minutes. For espresso, you’ll want your shot to pull in about 25-30 seconds. By adjusting that grind size you can find the sweet spot.

And that’s really the basics of the science of grind time! Just remember - more surface area means faster flow times, less surface area means longer extraction and flow restriction!