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How Grind Size Affects Espresso Extraction

Jan 8

Espresso grind size should be fine, but too fine is not better. It's been a mystery how to make espresso for a long time. Even the most skilled baristas occasionally make mistakes. If you use a super-automatic it's even worse.

One thing that is consistent though, is the espresso grind size. 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. This means that you can extract approximately 28% from a whole roasted coffee bean. 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. All the flavor is collected by the water on its way through.

You need to increase the coffee's surface area in order to make it taste better. This will create air pockets that allow water to enter the coffee beans and enhance their flavor. Coffee beans can be ground to increase their surface area. 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.

Acids and fats are the first compounds to be extracted from coffee. Acids are the simplest compounds and give coffee its sour flavor. This means that water is easy to dissolve them into the coffee. This is when many of the light aromas, such as the floral and fruity flavors, are extracted. Acids and light flavors are very important in our final cup, it's what give coffee its flavor.

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 don't want all soluble matters to end up in our cup. We don't want any of those compounds to be in our cup.

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 we don't stop the extraction in time, we obtain an over-extracted cup of coffee.

Below Extraction

Under-extraction is when the coffee doesn't contain enough soluble substances. The grounds often leave behind many flavors that balance your shot. 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 to strength. If you want a very strong coffee, you can use less water to increase the strength of the cup. It's possible, but not the best idea. It's harder to extract the best flavors of coffee the more you extract. The brew contains saturates. Even more important is the fact that coffee compounds have different concentration points so we can extract more during brewing. Because of this, a drip coffee that is brewed to an espresso strength does not taste good.

Espresso extraction will be affected by the size of your grind. Grind size is the most critical variable in 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 & Extraction

A pressure pump is used to force water through the "puck" of ground espresso. This produces thick, concentrated coffee.

Extra-fine grinder settings are 20 grams for a single shot espresso. This is done to increase the coffee’s surface area 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 Grind Size Affects 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. The lower extraction yields are bitter and taste more like sour than the higher ones.

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.

If you ever ground your coffee too fine, you know this. Coffee grounds too fine will prevent water from passing through them. The coffee grounds are too densely packed so water can't pass through.

The size of the coffee particles is part of the problem. You can compare sand to rocks. You have the same weight. You can pour water onto the rocks and it will instantly pass through. The water will take a while to reach the layers of sand if it is the same volume.

Tampering is another issue. When you tamp very finely ground coffee, you can pack it better, so the coffee puck is more compact. If you tamp the coffee too hard, it will reduce the flow.

The research team discovered that a slightly coarser grind, and a smaller amount of coffee per shot, is better. This results in a more full and even brewing process.

The Other Extreme

But, finer coffee can be just as troublesome as coarse coffee. The only thing you need to adjust is the grind size. These changes are not noticeable to the naked eye.

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 (and 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.

Double shots of coffee should weigh between 14 to 21 grams. For best results, try to keep the measurement within one gram of the number on the container.

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

Because they clog up the puck, the fines of a grinder are great because they help to improve the 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.

Don't Be Too Strict

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

It's because you can't take out the human element that is so beautiful about the industry. 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.