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The coarseness of the grind in coffee directly affects the contact area between the coffee and water as well as the extraction time, and it will directly affect the taste of the coffee. But at the same time, the coffee grind size is also the biggest headache for many people! In this article, Front Street will explain how to determine what the grind size should be for different coffee beans.

First, we must make sure that the single-origin coffee beans or espresso blend coffee beans we buy are freshly roasted!

When buying single-origin coffee beans or espresso beans, we must buy coffee beans whose packaging has a one-way exhaust valve and the coffee bean roasting date on it. The "one-way exhaust valve" (the button-shaped small hole at the top of the coffee bag) is designed to allow coffee beans to release naturally produced carbon dioxide while blocking other outside gases from entering the packaging. Every bag of coffee beans from Front Street Coffee (FrontStreet Coffee) is freshly roasted and uses packaging with a one-way exhaust valve.

After buying coffee beans, we can look at the roasting date, because coffee beans produce a large amount of carbon dioxide inside them during the roasting process, so we need to give the beans 3-7 days to release carbon dioxide on their own, commonly known as resting the beans. If we directly brew coffee beans that have just been roasted, the large amount of carbon dioxide continuously released during the brewing process will make the entire extraction process very unstable. So how long should they rest? Front Street suggests that light-medium roasted coffee beans should rest for 3-4 days, and medium-dark roasted coffee beans should rest for 4-5 days.

We just mentioned that the most direct manifestation of coffee bean freshness is the release of carbon dioxide from the coffee beans. In addition to carbon dioxide, the freshness of coffee beans also determines the aromatic substances responsible for the coffee's flavor and aroma. These small-molecule aromatic substances volatilize faster than the large-molecule substances that express coffee's bitterness, so the less fresh the coffee beans are, the less carbon dioxide and aromatic substances they have, and therefore the fewer extractable substances there are. Front Street suggests that roasted coffee beans are best finished within 2 months, and if they have already been ground into powder, they are best consumed within 20 days. If the coffee beans are already stale, no matter how you grind them, it won't help~

How does the coffee grind size affect the flavor of coffee?

1. At the same weight, the finer the grind, the more times it needs to be cut, the greater the surface area, and the greater the area where water can contact the coffee grounds.

2. The finer the grind, the finer the particles the coffee grounds are cut into  the shorter the distance from the surface of the coffee ground particles to their center  the shorter the time for water to reach the inner part of the coffee ground particles for extraction/the easier it is to extract the coffee's flavor substances.

Simply put, under otherwise identical parameters, the finer the particles, the higher the extraction yield; the finer the coffee is ground, the larger the contact area with water, and the higher the concentration of dissolved coffee; conversely, the coarser the coffee is ground, the smaller the contact surface area with water, and the lower the concentration of extracted coffee.

What happens if the coffee is ground too fine?

From the appearance of the particles, the particle size is smaller, and because the particles are smaller, the spacing between particles is shorter, making it harder for water to pass through, so the drip time during brewing is longer. A finer grind results in smaller coffee ground particles, increasing the surface area of the coffee particles and increasing the places where water can extract coffee substances, so the concentration and extraction yield increase; the coffee tastes rich, with obvious bitterness and astringency, while the other flavors are masked.

What happens if the coffee is ground too coarse?

From the appearance of the particles, the particle size is larger, and because the particles are larger, the spacing between particles is greater, making it easier for water to pass through the coffee grounds, so during brewing, the filtration time is shorter. A coarser grind results in larger coffee ground particles, reducing the surface area of the coffee particles and reducing the places where water can extract coffee substances, so the concentration and extraction yield also decrease; the coffee tastes weak and bland, with a light body and almost no flavor.

How do we determine the coffee grind size?

Front Street here recommends using a No. 20 sieve (mesh size 0.85mm) to calibrate the grind size. Then use 10g of coffee beans for a rough grind and pour them into the sieve for sifting. After completely sifting, see how much coffee powder finally falls into the tray under the sieve, and calibrate the grind size based on the passing rate. Front Street Coffee (FrontStreet Coffee) grind size standard sieve passing rate: cold brew > pour-over siphon 80% > moka American drip 75-80% >  cupping 70-75%  > French press 65-70%.

Of course, for coffee beans of different roast levels, the corresponding grind size used is also different. For example, Front Street brews light-roasted coffee with a grind size that has a passing rate of 80-85%% through a 0.85mm aperture sieve. Medium-roasted coffee uses a grind with a passing rate of 70%-75% through a 0.85mm aperture sieve. Dark-roasted coffee uses a grind with a passing rate of 65%-70% through a 0.85mm aperture sieve. But everyone's requirements for coffee richness are different. These data are for everyone's reference only, and you can still adjust to different degrees according to your own taste preference for strength.

What if you don't want to buy a coffee grind calibration sieve?!

Front Street knows that this whole process is quite troublesome, so here Front Street has made a small summary of coffee grind sizes, so you can see roughly which grind sizes your coffee brewing tools use. Front Street divides the coarseness of coffee grounds into 5 types: extra-fine, fine, medium-fine, medium, and coarse.

Coffee grind size fine powder 4 (from left to right: coarse, fine, extra-fine) 

Extra-fine: suitable for making espresso (moka pot, espresso machine)

When making espresso, you must tamp the coffee grounds firmly so that they create resistance to the high-pressure hot water, and only then can the essence of the coffee truly be extracted. The more uniform and delicate the grind, the tighter the coffee grounds after tamping, and the more balanced the resistance to water. Only then will the "pressed out" espresso have rich crema.

Fine: suitable for making drip bag coffee

This grind size is Front Street's "soul mate" for making drip bag coffee. The main reason is that drip bags are entirely made of filter paper, and the water flow is very large. Unlike pour-over, which has a narrowed opening, such as the commonly used three-hole dripper, which actually slows the speed of water flowing out, drip bags need fine grounds to increase the extraction area and extract more substances.

Medium-fine: suitable for brewing light-medium roasted coffee (various pour-over coffee drippers), recommended: Front Street Fruit Ding Ding, Front Street Huakui, Front Street Geisha, Front Street Strawberry Candy

When brewing light-medium roasted coffee beans, Front Street uses medium-fine grounds, about the size of fine granulated sugar, with a grind size between 75%-80% passing rate. Because light-medium roasted coffee beans generally have rich acidity, a medium-fine grind can improve the overall sweet-and-sour expression of the coffee~

Medium: suitable for brewing medium-dark roasted coffee (various pour-over coffee drippers), recommended: Front Street Jamaica Blue Mountain, Front Street Golden Mandheling, Front Street Huilan

When brewing medium-dark roasted coffee beans, Front Street uses medium grounds, about the size of coarse granulated sugar, with a grind size between 70%-75% passing rate. Medium grounds are not prone to producing extra-fine powder, and are also less likely to cause over-extraction due to unstable water flow control at the beginning that leads to a large amount of water accumulating in the dripper and soaking the coffee grounds.

Coarse: suitable for making coffee with a French press

The French press extracts the most original taste of coffee by steeping for 4 minutes. Compared with pour-over coffee, its coffee liquid is relatively cloudy because the metal filter has a larger pore size when filtering, so in terms of grind size we need to use coarse grounds. First, the coffee flavor is slowly extracted, and second, when the French press pushes down the filter, the coffee grounds will not "escape" through the gaps in the filter and mix with the coffee, affecting the mouthfeel when tasting.

The above content is compiled by CoffeeHunters, a coffee news website.