Espresso Extraction

[Esperanza Hession]

Espresso grind size should be just right, but the finer grind is not necessarily more beneficial. Making espresso has always been a mystery at some extent. Even the best baristas fail from time occasion. If you're using a super-automatic machine, barista, it's even more dangerous.

One thing that is consistent is the grind size of espresso is the same. In order to nail the perfect espresso shot that maintains some sweetness, and is not excessively bitter, you need to get the perfect grind size.

Espresso Extraction

About 28% of roast coffee beans are water-soluble. So, out of the whole coffee bean, one can get around 28 percent. The remaining is cellulose, and other plant materials that comprise the coffee bean's structure.

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Water needs help to dissolve soluble chemicals. If you pour coffee beans in hot water, they'll only dissolve the outside layer. The coffee bean's structure is very dense and complex therefore water won't be able to pass through easily. The water is able to absorb all the flavor.

Coffee tastes better when you increase the surface area of the bean. This leaves holes in the beans, which allow water to get into all flavors. Coffee beans are able to be ground to increase their surface area. The larger the surface area the greater the speed at which it reacts with water.

Water extracts flavor compounds in the following order regardless of how it is produced: fats, acids sugars, acid, fibers.

There are a few coffees whose flavorings are pleasant, so we need to manage the extraction process and stop it when the bitter compounds start to degrade. We don't want all the substance that is soluble to go into our coffee. Many of these compounds are not desirable, so we'd prefer not to extract these.

Fortunately, chemistry is with us on this, because most of the bitter compounds are difficult to extract, and if we stop extraction in time it will only yield the best substance.

Under Extraction

The cup you get will be that has too few solids soluble in the ground coffee. A lot of the flavors that give the balance of your shot aren't extracted from the grounds. And because acids are the compounds that extract the fastest, an unextracted shot might taste bitter, bizarrely salty, and devoid of sweetness.

The extraction of coffee is directly connected to its strength. If you want a very strong coffee, you can reduce the amount of water you use to boost the strength of your cup. Although it is possible, this isn't the most effective option. It is more difficult to extract the full flavor from coffee the more you use it. The brew gets saturated. The most important thing is the fact that coffee's components contain different saturation levels which means that we can take more of them off during the brewing. This is why a coffee made to the strength of espresso tastes awful.

It's fascinating to learn that scientists, baristas and roasters studied coffee extraction and discovered that a grind that is too fine won't produce the best tasting cup.

The Size of the Grind and Extraction

An espresso machine uses the pressure pump to push water through a "puck" of coffee ground. This makes a delicious and intense cup of coffee.

One of the most popular recipes for espresso is extra-fine grind that is around 20 grams for one espresso shot. The reason for this is to increase the coffee's surface area by water. The result is an increase in extraction yield. The extraction yield is the proportion of solids that are soluble and dissolving and are then incorporated into the final beverage.

How Grinder Size Affects Surface Area

An experiment conducted by Christopher Hendon, a computational chemist and a competitor barista, revealed that coffee shops aim to get extraction yields between 17 to 23 percent. Low extraction yields are sour tasting but higher yields can be too bitter.

They prepared thousands upon thousands of espresso shots and then developed a mathematical model that would define the variables needed to get consistent yield. They found that if coffee is ground too thin, the flow of coffee is at times too constrained and the shot can be over-extracted.

You know what happens when you grind your coffee too finely. If your coffee's grounds are too fine, water won't flow through. The puck isn't compact enough and water cannot pass through the tightly packed coffee grounds.

Part of the problem is the size of the coffee particles. A good example is the comparison between sand and rock. The same amount of sand and rocks is equal in weight. If you pour water over the rock, water will instantaneously go through. When you pour the same amount on the sand, it takes a little time to go through the layer of sand.

The other part of the issue is taping. Finely ground coffee better , and the puck will become more compact if tamp it. This restricts the flow even further if you tamp too heavily.

The team of researchers discovered that using a rougher grind and reducing amount of coffee ground per shot can be beneficial. This allows for greater amounts of coffee to be brewed which results in a richer and consistent drink.

The Other Extreme

However, coarser coffee can be similar to the finer ones. You only need very slight adjustments to the grind size, these changes are unnoticeable for the untrained eye.

Let's look at an extreme case when you are using for an espresso shot a medium grind, what is commonly used to prepare a drip coffee, your espresso will be poured in three seconds. This would be way too fast, and it will only draw out the acids. This will cause your coffee to be under-extracted.

Espresso Variables and Extraction

All things considered, roast degree will have the same effect on extraction. A darker roast can make it easier to extract the same coffee bean.

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

Tamping can alter the flow rate of your coffee which can affect the amount of coffee you can extract.

Grinder particles are useful because they can block the puck and aid in flow. They provide a 20-second contact time for water using coffee grounds. The use of too much precision can block the puck and cause the shot to stop flowing.

Don't Be Strict

Make sure not to cut off the creative aspect of coffee brewing.

The best part about coffee and the reason why people enjoy it so much is because you can't get rid of the human aspect. It's the scientific aspect that allows us make decisions about the flavor. It can be used to improve our coffee. But creativity and personal taste are equally important.