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How Grind Size Affects Espresso Extraction

Jan 9

Espresso grind size should not be too fine. It's been a mystery how to make espresso for a long time. Even the most experienced baristas make mistakes from time to time. It gets worse if you're using a super automatic.

One thing remains constant is the grind size of espresso. The perfect grind size is essential to achieve a perfect shot with sweetness and not too bitter.

Espresso Extraction

The water-soluble content of roasted coffee beans is around 28%. You can extract around 28% of the whole roasted coffee beans. The rest of the coffee bean's structure is made up cellulose and other plant matter.

Water needs help to dissolve soluble chemicals. You can only dissolve the outer layer of coffee beans by boiling them in hot water. Coffee beans are very dense and complicated, so water cannot pass through them easily. All the flavor is captured by the water as it passes through.

Coffee tastes better when you increase the bean's surface area. This will leave gaps in the beans that allow water to penetrate all the flavors. You can increase coffee beans' surface area by grinding the beans. The quicker the coffee reacts to water, the greater its surface area.

Water always extracts flavor compounds according to this order, regardless what method it uses: fats and acid, then sugars, then finally the plant fibres.

Acids (and fats) are the first substances to be extracted form coffee. Acids give coffee a bitter taste. It's easy to dissolve them in coffee water. At this point, many light aromas such as the fruity and floral flavors can be extracted. Coffee's flavor is derived from the acidity and light flavors in its final cup.

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 soluble matters to end up in our cup. We do not want many of those chemicals to go into our cups.

Chemistry can help us with this because most bitter compounds are difficult to extract. Therefore, if we stop extracting in time, we will only get the good stuff.

If we don't stop the coffee extraction at the right time, we can end up with a cup of coffee that is too extracted.


If you don't extract enough soluble solids from the ground coffee, the result is a cup that is under-extracted. Many of the flavors that add balance to your shot are not extracted from the grounds. Acids are the compounds that can extract the most quickly, which means that a shot with too much acid can taste weirdly salty or without sweetness.

Extraction is directly related. For a more strong coffee, use less water. This is not the best way to go, but it is possible. You can extract more coffee, but it's more difficult to extract all the flavor. The brew may contain saturates. More important, the saturation point of coffee compounds can vary. This allows us to extract more from them during brewing. Drip coffee is not good if it's brewed at an espresso strength.

Espresso extraction can be affected by the grind size. Grind size is the most important variable for espresso brewing.

Interesting is the fact that a group made up of scientists, coffee roasters, and baristas studied coffee extraction. They discovered that finer grinding doesn't give you the most flavorful cups.

The Grind Size (and Extraction)

An espresso machine uses a pressure pump to push water through a "puck", of ground coffee. This produces a dense and concentrated coffee.

Extra-fine grind settings, around 20g, are very popular for making espresso. It makes one shot of espresso. This is because it increases the coffee's surface area relative to water. In turn this should increase extraction yield. The extraction yield is the percentage of soluble solids that are dissolved and end up in the final beverage.

How Grin Size Affects the Surface Area

A University of Oregon study, led by Christopher Hendon (a computational chemist) and a competition barista revealed that most coffee shops seek an extraction yield of between 17-23 percent. Low extraction yields taste bitter and higher yields are more flavorful.

The team brewed thousands and thousands of espresso shots before developing a mathematical model that could pinpoint the variables necessary to ensure consistent yield. The team discovered that coffee ground too fine can cause a restricted flow and over-extracted shots.

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 size of the coffee particles is part of the problem. An example is the comparison of sand and rock. The same quantity of each is determined by its weight. When you pour water on the rocks, it will immediately pass through. If you pour the same quantity over the sand, it will take a bit of time to pass through the layer of sand.

Tampering is another problem. Tamping finely ground coffee will allow you to pack it better so that the coffee puck is compact. This restricts the flow even further, if you tamp too hard.

The research team discovered that a slightly coarser grind, and a smaller amount of coffee per shot, is better. This leaves some extra room in the coffee bed, leading to a fuller, more even brewing process.

The Other Extreme

However, coarser coffee is just as problematic as finer coffee. These adjustments can only be made to the grind size.

Let's take an extreme example: If you use for an espresso shot a medium grind, what is typically used for a drip coffee, your espresso will pour in 3 seconds. This would only extract the acids. The coffee will be severely under-extracted.

Espresso Variables and Extraction

Roast degree will affect the extraction of coffee beans in all cases. The same coffee bean will extract easier if it's roasted dark , compared to a lighter roast.

A double shot of coffee should be between 14 and 21 grams. You want to get the best possible results so that the cup weighs no more than one gram.

Tamping will affect the flow rate of your coffee, which in turn impacts how much of the ground coffee is extracted.

Fines from a grinder can be beneficial as they can clog pucks and improve flow. The coffee grounds and water have a contact time of 20 seconds. Too much finesse can clog the puck and cause the shot to not flow.

Don't Be Too Strict

Coffee brewing is a creative process.

The human component of coffee is what makes it so special and why people love it. It's important to recognize the scientific aspect of flavor and to be able to adjust our coffee to suit our tastes. However, creativity is just as important as personal taste.

This article was syndicated from Daily Preston UK News.