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How Grind Size Affects Espresso Extraction

Jan 2

Espresso grind size should be fine, but too fine is not better. Espresso making has been difficult to master for many years. Even the most experienced baristas make mistakes from time to time. It's worse if you use a superautomatic.

One thing that is consistent though, is the espresso grind size. The ideal grind size is crucial to getting the perfect shot. It will retain some sweetness while not being too bitter.

Espresso Extraction

Water-soluble coffee beans contain around 28%. This means that about 28% can be extracted from the entire roasted coffee bean. The rest of the coffee bean's structure is made up cellulose and other plant matter.

Water needs help to dissolve soluble chemicals. The coffee beans will only be dissolved if they are boiled in hot water. 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.

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. We can increase the surface area of coffee beans by grinding the beans. Coffee beans react faster to water if they have 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 give coffee a bitter taste. It's easy to dissolve them in coffee water. This is when many of the light aromas, such as the floral and fruity flavors, are extracted. It's the final cup that gives coffee its flavor.

Not all of the coffee's flavors are good, so we have to control the extraction and stop it just before the bitter compounds start to break down. We do not want all of the soluble matter to be 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.

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.

Under Extraction

The result of not extracting enough soluble solids out of the ground coffee is a cup that's under-extracted. A lot of the flavors that bring balance to your shot are left unextracted from the grounds. Acids are the compound that extract the most quickly so an under-extracted shot may taste strangely salty, sweet and lacking sweetness.

Extraction is directly related to strength. You can use less water to make a stronger cup. This is not the best way to go, but it is possible. It's harder to extract the best flavors of coffee the more you extract. The brew saturates. What is more important is that compounds in coffee have different saturation points , so we can extract more of them during brewing. Because of this, a drip coffee that is brewed to an espresso strength does not taste good.

Espresso extraction depends on the grind size. Grind size is the most important variable for 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 & Extraction

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

Extra-fine grind settings, around 20g, are very popular for making espresso. It makes one shot of espresso. This is done to increase the coffee’s surface area to water. This should result in a higher extraction yield. The extraction yield refers to the amount of soluble substances that dissolve, and ultimately ends up in the final drink.

How Grin Size Affects the Surface Area

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. The team discovered that coffee ground too fine can cause a restricted flow and over-extracted shots.

This is why you shouldn't grind your coffee too fine. Coffee grounds too fine will prevent water from passing through them. The puck is too compact, and water will not pass through the densely packed coffee grounds.

The problem lies in the size of coffee particles. You can compare sand to rocks. The same quantity of each is determined by its weight. When you pour water on the rocks, it will immediately pass through. It will take some time for the water to get through the layer of sand if you pour the same amount of water over the rocks.

Tampering is another issue. The best way to compact coffee is to tamp finely ground coffee. This reduces the flow of coffee if you tamp your beans too hard.

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 is also problematic. Only very minor adjustments are needed in the grind size.

Let's consider an extreme example. An espresso shot made with a medium-ground coffee will yield a 3 second pour. This would not extract the acids, as it would pour too quickly. You will find that your coffee is very under-extracted.

Espresso Variables and Extraction

Roast degree will affect the extraction of coffee beans in all cases. It'll extract coffee beans more efficiently if they are roasted at a darker roast than if they are roasted at a lighter temperature.

A double shot should contain between 14 and 21g of coffee. For best results, try to keep the measurement within one gram of the number on the container.

Tamping will alter the flow of your coffee. This in turn can impact the extraction of your coffee.

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. However, too much finesse could cause the puck to clog and the shot won't flow.

Don't Be Too Strict

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

A human component is one of the best things about coffee, and it's why people love it so much. It is the scientific component that allows us make decisions about flavor. We can use it to improve our coffee. But creativity and personal taste are equally important.

This article was syndicated from Daily Preston UK News.