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How Grind Size Affects Espresso Extraction

Jan 4

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 skilled baristas can make mistakes. It gets worse if you're using a super automatic.

The grind size is the most important thing about espresso. To get that perfect shot, which retains sweetness but isn't too bitter, you must grind the beans to the perfect size.

Espresso Extraction

Water-soluble coffee beans contain around 28%. This means that you can extract approximately 28% from a whole roasted coffee bean. The remainder of the coffee beans' structure is made up of cellulose and plant material.

Water needs help to dissolve soluble chemicals. Coffee beans can be disintegrated if they are heated to boiling water. 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.

Coffee tastes better when you increase the bean's surface area. Doing this will create gaps that allow water to permeate all the flavor. We can increase the surface area of coffee beans by grinding the beans. The quicker the coffee reacts to water, the greater its surface area.

Water always extracts flavor components in this order regardless how the method is used: fats and acids first, then sugars and finally the plant fibers.

Acids and fats were the first compounds that coffee can be extracted. Acids are the simplest compounds and give coffee its sour flavor. 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. Our final cup should contain both acidic and light flavors. This is what gives coffee its flavor.

We can't taste all the flavors in coffee so we need to control the extraction. We don't want all soluble matters to end up in our cup. Many of these compounds can be harmful and we don't want to extract them.

Fortunately, chemistry works with us on this, because most of the bitter compounds are harder to extract, so if we stop extraction in time, we 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.

Below Extraction

Under-extraction is when the coffee doesn't contain enough soluble substances. You can leave a lot of flavors in the coffee grounds that are essential for balance. And because acids are the compounds that extract the fastest, an under-extracted shot can taste sour, weirdly salty and without sweetness.

Extraction is directly related to strength. You can use less water to make a stronger cup. Although it is possible, this is not the best option. You can extract more coffee, but it's more difficult to extract all the flavor. The brew saturates. More important, the saturation point of coffee compounds can vary. This allows us to extract more from them during brewing. It is because we don't want to brew coffee at the right strength that it tastes bad.

Espresso extraction is directly influenced by the grind size. Grind size is the most critical variable in 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 relies on a pressure pump to force water through a "puck" of ground coffee. This creates a rich and concentrated cup of coffee.

Extra-fine grind settings, around 20g, are very popular for making espresso. It makes one shot of espresso. The purpose is to increase coffee's surface to water. This should lead to a greater extraction yield. The amount of soluble liquids that dissolve in the final beverage is called extraction yield.

How Grin Size Affects the Surface Area

A University of Oregon study led by Christopher Hendon and a competing barista found that most coffee shops want an extraction yield of 17 to 23 percent. Higher extraction yields can taste bitter, but lower yields will make you feel sour.

The team made thousands of espresso shots and created a mathematical model to determine the variables that were required for consistent yield. They found that coffee that is too finely ground can result in too much extraction.

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 tight and water cannot pass through the coffee grounds.

The problem lies in the size of coffee particles. An example is the comparison of sand and rock. The same amount of sand and rocks is equal in weight. You can pour water onto the rocks and it will instantly 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 issue. Tamping finely ground coffee will allow you to pack it better so that the coffee puck is compact. 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 results in a more full and even brewing process.

The Other Extreme

Finer coffee is equally problematic, however. These adjustments can only be made 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 only extract the acids. Your coffee will be extremely 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 dose of coffee should not exceed 14 grams. You want to get the best possible results so that the cup weighs no more than one gram.

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

The fines from a grinder are good because they clog the puck and help with the flow. They provide a 20 second contact time between water and coffee grounds. But too much finesse could clog the puck too much, and the shot will just not flow at all.

Don't Be Too Strict

You should not take the creativity out coffee brewing.

A human component is one of the best things about coffee, and it's why people love it so much. 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.