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How Grind Size Affects Espresso Extraction

Jan 10

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

One thing is certain, however: the espresso grind size. To get that perfect shot, which retains sweetness but isn't too bitter, you must grind the beans to the perfect size.

Espresso Extraction

The water-soluble content of roasted coffee beans is around 28%. This means that from the entire roasted bean you can extract only 28%. The rest of the coffee bean's structure is made up cellulose and other plant matter.

Water needs help to dissolve soluble chemicals. Coffee beans can be disintegrated if they are heated to boiling water. The coffee bean's structure is very dense and complex so water can't pass through easily. All the flavor is captured by the water as it passes through.

You can make coffee taste more delicious by increasing the beans' surface area. This will create air pockets that allow water to enter the coffee beans and enhance their flavor. The surface area of coffee beans can be increased by grinding them. The quicker the coffee reacts to water, the greater its 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.

The first compounds extracted from coffee are acids and fats. Acids are the simplest compounds and give coffee its sour flavor. It is therefore easy to dissolve these compounds in the coffee with water. Many of the light aromatics, for instance the the floral an d the fruity flavors are extracted at this moment. Acids and light flavors are very important in our final cup, it's what give coffee its flavor.

It is possible for coffee to have different flavors. Therefore, we have to control extraction and stop it as soon as the bitter compounds begin to break down. We do not want all of the soluble matter to be in our cup. We do not want many of those chemicals to go into our cups.

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.

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

Subtraction

A cup that doesn't have enough soluble coffee solids will result in a cup that is too extracted. A lot of the flavors that bring balance to your shot are left unextracted from the grounds. 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.

Strength is in a direct relationship to extraction. If you want a very strong coffee, you can use less water to increase the strength of the cup. While this may be possible, it's not the best. It's harder to extract the best flavors of coffee the more you extract. The brew will saturate. More important, the saturation point of coffee compounds can vary. This allows us to extract more from them during brewing. This is why a coffee that has been brewed to espresso strength tastes terrible.

Espresso extraction will be affected by the size of your grind. This is the most important variable when espresso brewing.

It's fascinating to note that scientists, baristas and roasters studied coffee extraction and found that too fine a grinding won't produce the best tasting cup.

The Grind Size, and Extraction

An espresso machine is powered by a pressure pumps to force water through a cup of ground coffee. This produces thick, concentrated coffee.

A very popular recipe for espresso is extra-fine grind settings around 20 grams to brew a single shot of espresso. This is done in order to increase coffee's surface area. This should increase extraction yield. Extraction yield refers to how much of the soluble solids are removed and what end up in final beverages.

How does the grind size affect surface area

A University of Oregon study by Christopher Hendon was conducted with a barista and computational chemist. It showed that coffee shops tend to aim for extraction rates between 17 percent and 23 percent. A lower extraction yield is more bitter than a higher one.

They brewed thousands upon thousands of espresso shots, and then developed a mathematical model that would pinpoint the variables needed to achieve consistent yield. They found that coffee that is too finely ground can result in too much extraction.

Don't grind your coffee any finer than necessary. Coffee grounds too fine will prevent water from passing through them. Water cannot pass through tightly packed coffee grounds because the puck is too small.

The coffee particle size is one of the problems. One good example is the comparison between rocks and sand. You have the same weight. When you pour water on the rocks, it will immediately pass through. It may take a bit longer for water to flow through the layer made of sand when you pour the same amount.

Tampering is also a problem. 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.

According to the research team, a coarser grind is more effective than using less coffee per cup. This leaves some extra room in the coffee bed, leading to a fuller, more even brewing process.

The Other Extreme

However, coarser coffee is just as problematic as finer coffee. 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. It would extract only the acids and be too fast. Your coffee will be extremely under-extracted.

Espresso Variables and Extract

All things equal, roast degree will have as well an impact on the extraction. It will extract the same coffee bean more efficiently if it is roasted darkly than if it is roasted lighter.

A double shot of coffee should be between 14 and 21 grams. To achieve the best results, limit the measurement to one gram of what is printed on the carton.

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

Because they clog up the puck, the fines of a grinder are great because they help to improve the flow. They reduce the contact time of water and coffee grounds by 20 seconds. Too much finesse can clog the puck and cause the shot to not flow.

Don't Be Too Strict

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

The beauty of coffee and the reason people love it so much is that you can't get rid of the human component. 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.