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How Grind Size Affects Espresso Extraction

Jan 10

Espresso should not be too fine. Making espresso has always been a mystery to some degree. Even the most skilled baristas have made mistakes. You can make it worse by 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

Roasted coffee beans are about 28% water-soluble. That means that out of the entire roasted coffee bean, you can extract about 28%. The remainder is cellulose and other plant material that make up the coffee bean's structure.

Water needs help to dissolve soluble chemicals. When you boil coffee beans, the outside layer is not dissolved. Coffee beans are very dense and complicated, so water cannot pass through them easily. All the flavor is collected by the water on its way through.

Coffee tastes better when you increase the bean's surface area. This will result in gaps that let water through to the coffee, which allows for all its flavor. Coffee beans can be ground to increase their surface area. The faster it reacts with water, the more 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 were the first compounds that coffee can be extracted. Acids, which give coffee a sour taste, are the simplest compounds. This makes it easy for water to dissolve them in the coffee. 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.

Some coffees have a different flavor. We need to control how the extraction is done and stop it before bitter compounds begin to dissolve. We do not want all of the soluble matter to be in our cup. Many of these compounds can be harmful and we don't want to extract them.

Chemistry is a great partner in this endeavor, as bitter compounds can be difficult to extract. If we stop extraction at the right time, we get only the good stuff.

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


If you don't extract enough soluble solids from the ground coffee, the result is a cup that is under-extracted. You can leave a lot of flavors in the coffee grounds that are essential for balance. 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. For a more strong coffee, use less water. It's possible, but not the best idea. You can extract more coffee, but it's more difficult to extract all the flavor. The brew will saturate. What is more important is that compounds in coffee have different saturation points , so we can extract more of them during brewing. This is why a coffee that has been brewed to espresso strength tastes terrible.

Espresso extraction is directly influenced by the grind size. This is the most important variable when espresso brewing.

It is fascinating that a group composed of baristas as well as a roaster and scientists looked at coffee extraction. They found that grinding coffee too finely doesn't result in the best cup.

The Grind Size and Extraction

An espresso machine is powered by a pressure pumps to force water through a cup of ground coffee. This produces thick, concentrated coffee.

A very popular recipe for espresso is extra-fine grind settings around 20 grams to brew a single shot of espresso. This is done to increase the coffee’s surface area to water. This should increase 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 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 that is too finely ground can result in too much extraction.

This is why you shouldn't grind your coffee too fine. If your coffee grinds are too fine, water will not pass through. The puck is too compact and water cannot pass through the tightly packed coffee grounds.

The size of the coffee particles is part of the problem. The comparison of rocks and sand is a good example. You have the same weight. You can pour water onto the rocks and it will instantly pass through. It may take a bit longer for water to flow through the layer made of sand when you pour the same amount.

Tampering is also a problem. Because finely ground coffee can be packed better, the coffee puck will be compacted. If you tamp the coffee too hard, it will reduce the flow.

Research team discovered that a coarser grind and less coffee per shot are better. This results in a more full and even brewing process.

The Other Extreme

Finer coffee can also be problematic. Only very minor adjustments are needed in 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. It would extract only the acids and be too fast. The coffee will be severely under-extracted.

Espresso Variables, and Espresso Extraction

Roast degree will affect the extraction of coffee beans in all cases. If the coffee bean is roasted darker than a lighter roast, it will extract more easily.

Double shots of coffee should weigh between 14 to 21 grams. To get the best results, keep the amount within 1 gram of the number printed on the container.

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 are good as they clog your puck and increase flow. They create a 20-second contact time for water with coffee grounds. But too much finesse could clog the puck too much, and the shot will just not flow at all.

Do not be too strict

Make sure not to take the creativity out of coffee brewing.

The beauty of coffee and the reason people love it so much is that you can't get rid of the human component. While the scientific component is essential in making decisions about flavor, it also allows us to make choices to improve our coffee. However, creativity and personal tastes are equally important.

This article was syndicated from Daily Preston UK News.