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How Grind Size Affects Espresso Extraction

Jan 8

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. You need the right grind size to ensure a perfect shot.

Espresso Extraction

Water-soluble coffee beans contain around 28%. 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. If you throw coffee beans in hot water, they only dissolve the outside layer. The structure of coffee beans is complex and dense so that water cannot easily pass through. 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. Doing this will create gaps that allow water to permeate all the flavor. By grinding coffee beans, we can increase the coffee bean's surface area. Coffee beans react faster to water if they have more surface area.

Water extracts all flavor compounds in this order no matter what method.

Acids and fats are the first compounds to be extracted from coffee. Acids, which give coffee a bitter taste, are the easiest compounds to extract. This makes it easy for water to dissolve them in the coffee. 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.

The coffee may not have all the right flavors so we must control the extraction to stop the bitter compounds from forming. We do NOT want all soluble material to make it into our cups. We do not want many of those chemicals to go into our cups.

Chemistry works well with us because bitter compounds are more difficult to extract. We can stop extracting them in time so that 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

A cup that doesn't have enough soluble coffee solids will result in a cup that is too 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.

Extraction is directly related to strength. You can use less water to make a stronger cup. Not the best idea, though possible. It's harder to extract the best flavors of coffee the more you extract. The brew may contain saturates. It is important to note that different saturation levels of compounds in coffee can be used to extract more. Drip coffee is not good if it's brewed at an espresso strength.

Espresso extraction can be affected by the grind size. This is the most important variable when 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 (and Extraction)

An espresso machine works by using a pressure pump that pushes water through a "puck” of ground coffee. This produces a thick and concentrated coffee.

A very popular recipe for espresso is extra-fine grind settings around 20 grams to brew a single shot of espresso. The reason is to increase the coffee's surface area to water. This should increase extraction yield. Extraction yield measures the amount of soluble solids that dissolve and ends up in the final beverage.

How Grin Size Affects the Surface Area

A University of Oregon study, led by Christopher Hendon (a computational chemist) and a competition barista revealed that most coffee shops seek an extraction yield of between 17-23 percent. Higher extraction yields can taste bitter, but lower yields will make you feel sour.

They made thousands of espresso shots. Then they developed a mathematical formula to identify the variables that are required to produce consistent yield. They found that coffee can be too finely ground, which results in a shot being too concentrated.

If you ever ground your coffee too fine, you know this. Water just doesn't pass through the coffee grinds, if the grounds are too fine. The coffee grounds are too densely packed so water can't pass through.

Coffee particle size is a major problem. An example is the comparison of sand and rock. The same quantity is available by weight. When you pour water on the rocks, it will immediately pass through. The water will take a while to reach the layers of sand if it is the same volume.

Tampering is also a problem. Tamping finely ground coffee will allow you to pack it better so that the coffee puck is compact. This reduces the flow of coffee if you tamp your beans too hard.

The research team found out that using a slightly coarser grind and reducing the amount of ground coffee per shot is better. 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. You only need very slight adjustments in grind size, these changes are unnoticeable to the naked eye.

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. You will find that your coffee is very under-extracted.

Espresso Variables (and Extraction)

All things equal, roast degree will have as well an impact on the extraction. It'll extract coffee beans more efficiently if they are roasted at a darker roast than if they are roasted at a lighter temperature.

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 alter the flow rate and therefore the amount of coffee that is extracted.

Grinder fines are beneficial because they can clog the puck and aid in 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 rigid

You should not take the creativity out 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.

This article was syndicated from Daily Preston UK News.