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How Grind Size Affects Espresso Extraction

Jan 3

Espresso grind size shouldn't be too fine. It has been a mystery for some time how to make espresso. Even the most skilled baristas have made mistakes. It gets worse if you're using a super automatic.

One thing is certain, however: the espresso grind size. In order to nail that perfect shot that retains some sweetness, and is not overly bitter, you need to get the perfect grind size.

Espresso Extraction

About 28% of roasted coffee beans is water-soluble. This means that you can extract approximately 28% from a whole roasted coffee bean. The remainder is cellulose and other plant material that make up the coffee bean's structure.

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. The water is able to collect all the flavor.

To make coffee taste better, you need to increase the surface area of the beans. Doing this will create gaps that allow water to permeate all the flavor. You can increase coffee beans' surface area by grinding the beans. The more surface area, the quicker it reacts to water.

Water extracts flavor compounds in the following order, regardless of how it is made: fats, acids, sugars, and then the plant fibers.

Acids and fats are the first compounds to be extracted from coffee. Acids, which give coffee a sour taste, are the simplest compounds. It is easy to dissolve these compounds into coffee. This is the time when most of the light aromatics are extracted, including the floral and fruity flavor. Coffee's flavor is derived from the acidity and light flavors in its final cup.

The coffee may not have all the right flavors so we must control the extraction to stop the bitter compounds from forming. We do NOT want all soluble material to make it into our cups. Many of these compounds can be harmful and we don't want to extract them.

Chemistry works well with us because bitter compounds are more difficult to extract. We can stop extracting them in time so that we only get the good stuff.

We can get a coffee with too much caffeine if we don’t stop the extraction at the correct time.


A cup that doesn't have enough soluble coffee solids will result in a cup that is too extracted. Most of the flavors that give balance to your shot aren't extracted from the ground coffee. Acids are the most efficient extractors of compounds, so a shot that is under-extracted can taste strangely salty, bitter, and devoid of sweetness.

Extraction is directly related to strength. You can use less water to make a stronger cup. Not the best idea, though possible. It is more difficult to extract all the flavors from coffee the more you extract it. The brew saturates. It is important to note that different saturation levels of compounds in coffee can be used to extract more. This is why a coffee that has been brewed to espresso strength tastes terrible.

Espresso extraction will be affected by the size of your grind. This is the most important variable in the espresso brewing.

What's interesting is that a group of baristas, roaster, and scientists studied coffee extraction and discovered that grinding too finely won't yield the most flavorful cup.

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 grinder settings are 20 grams for a single shot espresso. This is done in order to increase coffee's surface area. This should result in a higher extraction yield. The extraction yield is the percentage of soluble solids that are dissolved and end up in the final beverage.

Surface Area and Grind Size

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. A lower extraction yield is more bitter than a higher one.

The team made thousands of espresso shots and created a mathematical model to determine the variables that were required for consistent yield. The team discovered that coffee ground too fine can cause a restricted flow and over-extracted shots.

Don't grind your coffee any finer than necessary. If your coffee grinds are too fine, water will not pass through. The coffee grounds are too densely packed so water can't pass through.

Coffee particle size is a major problem. The comparison of rocks and sand is a good example. You have the same quantity by weight. The rocks will absorb water if you pour it on. 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. Because finely ground coffee can be packed better, the coffee puck will be compacted. This can also reduce the flow if you tamp it too hard.

Researchers discovered that a coarser coffee grind and a lower amount of ground coffee per cup is better. This creates more room in the coffee bed and results in a more satisfying brewing experience.

The Other Extreme

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

Let's look at an extreme example. If you use a medium grind for espresso shots, which is what is used for drip coffees, your espresso will pour in three seconds. This would make it impossible to extract the acids. The coffee will be severely under-extracted.

Espresso Variables & Extraction

All things being equal, the roast degree will impact the extraction. It will extract the same coffee bean more efficiently if it is roasted darkly than if it is roasted lighter.

A double dose of coffee should not exceed 14 grams. For best results, try to keep the measurement within one gram of the number on the container.

Tampering can affect the flow rate of your coffee which will in turn impact how much coffee you extract.

Grinder fines are beneficial because they can clog the puck and aid in 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.

The beauty of coffee and the reason people love it so much is that you can't get rid of the human component. 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.