What's the Difference in Coffee Grind Sizes? How Fine Should Espresso Be? How Coarse Should Pour-Over Be?

The Science of Coffee Grinding: Unlocking Flavor Through Extraction

Extraction is the process of using water as a medium to dissolve flavor compounds from coffee beans. Before extraction can occur, we must first grind coffee beans using a grinder, as this allows the flavor compounds within the coffee to dissolve more quickly and easily. This is what we commonly refer to as coffee grinding.

Coffee grinding typically takes priority over other extraction parameters because, as FrontStreet Coffee mentioned at the beginning, the coarseness of the grind determines the speed at which flavor compounds dissolve. Scientific research shows that when coffee beans are ground into powder, their surface area increases approximately 1,000 times compared to their original state. The finer the grind, the greater the surface area increase, and the shorter the linear distance from the particle surface to its center (affected by burr design). Conversely, coarser grinds result in less surface area increase and longer linear distances from surface to center.

The increase in surface area allows coffee grounds to have more contact area with water, while the length of the linear distance to the center determines the time required for water to penetrate into the interior of coffee particles. This means that when coffee is ground finer, it has more surface area, a shorter distance from surface to interior, and hot water can dissolve flavor compounds more quickly, and vice versa. Therefore, regardless of the extraction method used, coffee grinding typically has the highest priority. We need to find the corresponding grind size before we can begin extracting a good cup of coffee.

Matching Grind Sizes to Different Brewing Methods

So what grind sizes correspond to different coffee extraction methods? This is undoubtedly a question many friends want answered! However, because everyone uses different grinders and coffee beans, and because grind sizes cannot be standardized, we generally can only share ranges with you in broad terms. For example, coarse sugar grind, fine sugar grind, or flour-like grind, among others.

Regarding what grind size to use for what extraction method, you can refer to the detailed article "Coffee Grinding Reference." Alternatively, we can directly calculate the required coffee grind coarseness based on the average extraction time of that brewing method (of course, this requires having a reference point!). The longer the extraction time required, the relatively coarser the grind size needed. When the extraction time required is shorter, the coffee grind will be relatively finer. For example, espresso extraction. We need to extract coffee within about 30 seconds (example, not absolute), so the coffee particle size must be very, very fine! Only then can hot water dissolve all the flavor compounds from the coffee grounds in a short time.

However, because espresso extraction is pressurized and involves many factors, we can look at it from another angle, such as pour-over coffee and siphon brewing. The average extraction time for pour-over coffee is about 2 minutes, while siphon brewing is within 1 minute. Therefore, siphon brewing requires a finer coffee grind than pour-over coffee. Following this logic, we can calculate the coffee grind sizes needed for different extraction methods! (With the exception of specialty coffees like Turkish coffee). To return to why coffee grinding cannot be standardized, the reason is actually quite simple: the coffee particles we grind are not absolutely uniform in size! This is a point that FrontStreet Coffee often mentions.

The Importance of Grind Uniformity

Why aren't ground particles absolutely uniform? Regardless of the quality of the grinder, the resulting coffee grounds will never be absolutely uniform. There are both large particles and small ones. This is related to the characteristics of the beans and the burrs and motor of the grinder. It is precisely because they are not absolutely uniform that the coffee we brew can have more complexity. Therefore, we measure the quality of a coffee grind by its uniformity—higher uniformity means better grinding quality, and vice versa. (The image below shows 15g of coffee ground with an Ek43, with particles arranged from large to medium to fine from left to right)

Regardless of what grinder or burrs are used, the grinding process is always accompanied by crushing. Crushing promotes the generation of fine particles—the more crushing that occurs and the longer the grinding time, the more fine particles are produced (different burrs also produce different particle shapes). The presence of an appropriate amount of fine particles helps increase complexity, but it's also a double-edged sword! Too many fine particles can easily lead to extraction issues like clogging and uneven extraction. Therefore, we can see that highly uniform coffee grounds are crucial for brewing (ideally, fine particles should account for 3%-5% of the total grounds).

How Coffee Bean Characteristics Affect Grinding

The characteristics of coffee beans also affect grinding. Friends who have used manual grinders should be very clear about this point. Grinding beans with different characteristics feels completely different—some beans are difficult to grind, while others grind quickly with just a few turns. This is mainly influenced by the roast level and density of the coffee beans.

When coffee beans are roasted darker, their density becomes lower, while their brittleness increases, making them easier to grind. This is because, like a cookie, we can easily break it in two with just a gentle snap. When coffee beans are roasted lighter, their density is higher, while their brittleness is lower, making grinding more difficult. However, we need to note that when coffee beans are more brittle, they more easily produce fine particles. To use the cookie example again: after breaking a cookie, besides the two intended pieces, don't we also get many small crumbs? This is caused by the cookie's brittleness. The same principle applies to coffee bean grinding! With the same grind setting, more brittle coffee beans will produce more fine particles, resulting in an overall finer grind compared to less brittle beans.

In addition to roast level, the processing method, growing altitude, and variety of coffee beans all affect their density. When coffee beans have higher density, we need to use a finer grind because denser beans are more difficult to extract. Lower density beans require determining the grind degree based on roast level and processing method. Darker roasted coffee beans require coarser grinding to prevent over-extraction due to excessive extraction efficiency. If the lower density is caused by processing methods, the grind adjustment can be determined based on the brewing state and coffee taste.

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