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How Grind Size Affects Espresso Extraction

Jan 5

Espresso grind size should not be too fine. Espresso has always been a mysterious process. Even the most skilled baristas sometimes make mistakes. It's worse if you use a superautomatic.

The grind size is the most important thing about espresso. You need the right grind size to ensure a perfect shot.

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. 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. The water is able to collect all the flavor.

You can make coffee taste more delicious by increasing the beans' surface area. This will leave gaps in the beans that allow water to penetrate all the flavors. The surface area of coffee beans can be increased by grinding them. 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) are the first substances to be extracted form coffee. Acids, which give coffee a sour taste, are the simplest compounds. This makes it easy for water to dissolve them in the coffee. Many of the light aromatics, for instance the the floral an d the fruity flavors are extracted at this moment. The final cup will contain acidic and light flavorings. They are what give coffee its unique 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 don't want all soluble matters to end up in our cup. Many of these compounds are not desirable, so we try to avoid extracting them.

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.

We can get a coffee with too much caffeine if we don’t stop the extraction at the correct time.

Under-Extraction

If you don't extract enough soluble solids from the ground coffee, the result is a cup that is under-extracted. The grounds often leave behind many flavors that balance your shot. Acids are what extract the fastest so shots that have been underextracted can taste strangely sweet, salty, or bitter.

The extraction of coffee is directly related to the strength. 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 saturates. What is more important is that compounds in coffee have different saturation points , so we can extract more of them during brewing. It is because we don't want to brew coffee at the right strength that it tastes bad.

Espresso extraction depends on the grind size. This is the most important variable when 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 works by using a pressure pump that pushes water through a "puck” of ground coffee. This creates a rich and concentrated cup of 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. In turn this should increase extraction yield. Extraction yield refers to how much of the soluble solids are removed and what end up in final beverages.

Surface Area: How Grinder Size Influences

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. Higher extraction yields can taste bitter, but lower yields will make you feel sour.

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

You know what happens when you grind your coffee too finely. If your coffee grinds are too fine, water will not pass through. The coffee grounds are too densely packed so water can't pass through.

Coffee particle size is a major problem. One good example is the comparison between rocks and sand. You have the same quantity by 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.

The other problem is the tamping. Tamping finely ground coffee will allow you to pack it better so that the coffee puck is compact. This can also reduce the flow if you tamp it too hard.

Research team discovered that a coarser grind and less coffee per shot are better. This creates more room in the coffee bed and results in a more satisfying brewing experience.

The Other Extreme

However, coarser coffee is just as problematic as finer coffee. These changes can be made by making very minor adjustments to 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. This will cause your coffee to be very under-extracted.

Espresso Variables and Extract

The roast degree can have an effect on extraction, but it is not a determining factor. The same coffee bean will extract easier if it's roasted dark , compared to a lighter roast.

A double dose of coffee should not exceed 14 grams. The best results are achieved when the quantity is within one gram.

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. The coffee grounds and water have a contact time of 20 seconds. The shot may not flow if there is too much finesse.

Don't be too strict

Don't let your creativity get in the way 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 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.