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How Grind Size Affects Espresso Extraction

Jan 3

Espresso grind size should not be too fine. It's been a mystery how to make espresso for a long time. Even the most skilled baristas have made mistakes. It gets worse if you're using a super automatic.

One thing that is consistent though, is the espresso grind size. In order to nail that perfect shot that retains some sweetness, and is not overly bitter, you need to get the perfect grind size.

Espresso Extraction

About 28% of roasted coffee beans is water-soluble. This means that from the entire roasted bean you can extract only 28%. The remainder of the coffee beans' structure is made up of cellulose and plant material.

Water needs help to dissolve soluble chemicals. The coffee beans will only be dissolved if they are boiled in hot water. The structure of the coffee bean is extremely dense and complex. Water can't penetrate it easily. All the flavor is captured by the water as it passes through.

You need to increase the coffee's surface area in order to make it taste better. This will leave gaps in the beans that allow water to penetrate all the flavors. We can increase the surface area of coffee beans by grinding the beans. The faster it reacts with water, the more 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, are the first compounds taken from coffee. Acids are the most basic compounds, and they give coffee a sour flavour. This means that water is easy to dissolve them into the coffee. This is the time when most of the light aromatics are extracted, including the floral and fruity flavor. Coffee's flavor is derived from the acidity and light flavors in its final cup.

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. A lot of those compounds are undesirable, and we want to avoid extracting those.

Chemistry is helpful because most bitter compounds can be hard to extract so we need to stop extracting too soon.

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

The Extraction

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 compound that extract the most quickly so an under-extracted shot may taste strangely salty, sweet and lacking sweetness.

Extraction is directly related with strength. To get a strong cup of coffee, you can reduce the amount of water you use. 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 contains saturates. It is important to note that different saturation levels of compounds in coffee can be used to extract more. It is because we don't want to brew coffee at the right strength that it tastes bad.

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

It is interesting to note that a group consisting of baristas, scientists, and roasters looked into coffee extraction and discovered that the finest grinds don't always yield the best flavor.

The Grind Size, and Extraction

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

Extra-fine grind settings of around 20 grams are a popular way to make espresso. This allows you to brew one shot. The purpose is to increase coffee's surface to water. In turn this should increase 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 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. Lower extraction yields taste sour, while higher yields are too bitter.

The team made thousands of espresso shots and created a mathematical model to determine the variables that were required for consistent yield. They discovered that when coffee is ground too fine, the flow is sometimes too restricted and the shot is over-extracted.

You know what happens when you grind your coffee too finely. 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 coffee particle size is one of the problems. One good example is the comparison between rocks and sand. The same amount of sand and rocks is equal in weight. If you pour some water on the rocks, water will instantaneously go through. If you pour the same quantity over the sand, it will take a bit of time to pass through the layer of sand.

The other problem is the tamping. You can pack finely ground coffee better and the puck will be more compact if you tamp it. If you tamp too hard, this can reduce the flow.

Research team discovered that a coarser grind and less coffee per shot are better. This allows for more coffee to be brewed, which results in a richer and more consistent brew.

The Other Extreme

Finer coffee can also be problematic. These changes can be made by making very minor adjustments to the grind size.

Let's take an extreme example: If you use for an espresso shot a medium grind, what is typically used for a drip coffee, your espresso will pour in 3 seconds. It would extract only the acids and be too fast. The coffee will be severely under-extracted.

Espresso Variables (and Extraction)

The roast degree can have an effect on extraction, but it is not a determining factor. A darker roast will make it easier to extract the same coffee bean.

Double shots of coffee should weigh between 14 to 21 grams. The best results are achieved when the quantity is within one gram.

Tamping can reduce the flow rate, which will impact the extraction.

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. Too much finesse can clog the puck and cause the shot to not flow.

Don't be strict!

Don't let your creativity get in the way of coffee brewing.

The human component of coffee is what makes it so special and why people love it. 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.