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How Grind Size Affects Espresso Extraction

Jan 7

Espresso grind size should be fine, but too fine is not better. Making espresso has always been a mystery to some degree. Even the most experienced baristas make mistakes from time to time. You can make it worse by using a super-automatic.

One thing is certain, however: the espresso grind size. The ideal grind size is crucial to getting the perfect shot. It will retain some sweetness while not being too bitter.

Espresso Extraction

The water-soluble content of roasted coffee beans is around 28%. That means that out of the entire roasted coffee bean, you can extract about 28%. The rest is mostly cellulose and plant stuff which makes up the coffee bean's structure.

Water needs help to dissolve soluble chemicals. If you throw coffee beans in hot water, they only dissolve the outside layer. The structure of the coffee bean is extremely dense and complex. Water can't penetrate it easily. The water is able to collect all the flavor.

The bean's surface area must be increased to make coffee more flavorful. This will allow water to seep through the beans, allowing for all the flavor. You can increase coffee beans' surface area by grinding the beans. The coffee beans will react to water faster if there is more surface area.

Water extracts all flavor compounds in this order no matter what method.

The first compounds extracted from coffee are acids and fats. Acids, which give coffee a sour taste, are the simplest compounds. It is easy to dissolve these compounds into coffee. At this point, many light aromas such as the fruity and floral flavors can be extracted. It's the final cup that gives coffee its flavor.

It is possible for coffee to have different flavors. Therefore, we have to control extraction and stop it as soon as the bitter compounds begin to break down. We don't want all the soluble matter to get into our coffee. We do not want many of those chemicals to go into our cups.

Chemistry is helpful because most bitter compounds can be hard to extract so we need to stop extracting too soon.

However, if the extraction is not stopped in time, then we get an over-extracted cup.


The result of not extracting enough soluble solids out of the ground coffee is a cup that's under-extracted. You can leave a lot of flavors in the coffee grounds that are essential for balance. Acids are the compound that extract the most quickly so an under-extracted shot may taste strangely salty, sweet and lacking sweetness.

Strength is in a direct relationship to extraction. If you want a very strong coffee, you can use less water to increase the strength of the cup. While this may be possible, it's not the best. The more coffee you extract, the more difficult it is to extract out all of the good flavors. The brew contains saturates. Even more important is the fact that coffee compounds have different concentration points so we can extract more during brewing. Drip coffee is not good if it's brewed at an espresso strength.

Espresso extraction is affected by the grind size. Grind size is the most critical variable in espresso brewing.

It is interesting to note that a group consisting of baristas, scientists, and roasters looked into coffee extraction and discovered that the finest grinds don't always yield the best flavor.

The Grind Size & Extraction

An espresso machine relies on a pressure pump to force water through a "puck" of ground coffee. This produces thick, concentrated coffee.

Extra-fine grind settings at around 20 grams is a very popular method to make espresso. The purpose is to increase coffee's surface to water. This will increase the extraction yield. Extraction yield measures the amount of soluble solids that dissolve and ends up in the final beverage.

How Grind Size Affects Surface Area

A study from the University of Oregon led by Christopher Hendon , a computational chemist, and a competitive barista showed that most coffee shops aim for an extraction yield between 17 to 23 percent. Lower extraction yields taste sour, while higher yields are too bitter.

The team brewed thousands and thousands of espresso shots before developing a mathematical model that could pinpoint the variables necessary to ensure consistent yield. They found that coffee can be too finely ground, which results in a shot being too concentrated.

If you ever ground your coffee too fine, you know this. If the grounds are too fine, water won't pass through. The puck is too compact, and water will not pass through the densely packed coffee grounds.

The problem lies in the size of coffee particles. An example is the comparison of sand and rock. You have the same weight. When you pour water on the rocks, it will immediately pass through. The water will take a while to reach the layers of sand if it is the same volume.

The other part of the problem is the tamping. When you tamp very finely ground coffee, you can pack it better, so the coffee puck is more compact. This can also reduce the flow if you tamp it too hard.

The research team found out that using a slightly coarser grind and reducing the amount of ground coffee per shot is better. This gives you more space in your coffee bed which leads to a better brewing process.

The Other Extreme

Finer coffee is equally problematic, however. These changes can be made by making very minor adjustments to the grind size.

Let's try an extreme example. Espresso shot with medium grind coffee (which is the same as a drip coffee) will take 3 seconds to pour. This would only extract the acids. Your coffee will be extremely under-extracted.

Espresso Variables & Extraction

The roast degree can have an effect on extraction, but it is not a determining factor. The same coffee bean will extract easier if it's roasted dark , compared to a lighter roast.

A double shot should contain between 14 and 21g of coffee. To get the best results, keep the amount within 1 gram of the number printed on the container.

Tamping can alter the flow rate and therefore the amount of coffee that is extracted.

Fines from a grinder are good as they clog your puck and increase flow. They provide a 20 second contact time between water and coffee grounds. The shot may not flow if there is too much finesse.

Don't be too strict

Coffee brewing is a creative process.

It's because you can't take out the human element that is so beautiful about the industry. It is the scientific component that allows us make decisions about flavor. We can use it to improve our coffee. But creativity and personal taste are equally important.

This article was syndicated from Daily Preston UK News.