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How Grind Size Affects Espresso Extraction

Jan 4

Espresso should be ground to a fine grind, but not too fine. Espresso making has been difficult to master for many years. Even the most experienced baristas make mistakes from time to time. It gets worse if you're using a super automatic.

The grind size is the most important thing about espresso. The ideal grind size is crucial to getting the perfect shot. It will retain some sweetness while not being too bitter.

Espresso Extraction

Coffee beans are approximately 28% water-soluble. This means that you can extract approximately 28% from a whole roasted coffee bean. The rest is cellulose, plant matter and other materials that form the coffee bean’s structure.

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. The water is able to collect all the flavor.

Coffee tastes better when you increase the bean's surface area. This will result in gaps that let water through to the coffee, which allows for all its flavor. Coffee beans can be ground to increase their surface area. The faster it reacts with water, the 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 are the simplest compounds and give coffee its sour flavor. It is easy to dissolve these compounds into coffee. At this point, many light aromas such as the fruity and floral flavors can be extracted. It's the final cup that gives coffee its flavor.

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. 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.

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

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. And because acids are the compounds that extract the fastest, an under-extracted shot can taste sour, weirdly salty and without sweetness.

Extraction is directly related with strength. To get a strong cup of coffee, you can reduce the amount of water you use. 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 contains saturates. What is more important is that compounds in coffee have different saturation points , so we can extract more of them during brewing. Drip coffee is not good if it's brewed at an espresso strength.

Espresso extraction will be affected by the size of your grind. This variable is crucial in espresso brewing.

What's interesting is that a group of baristas, roaster, and scientists studied coffee extraction and discovered that grinding too finely won't yield the most flavorful cup.

The Grind Size and Extraction

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

Extra-fine grind settings, around 20g, are very popular for making espresso. It makes one shot of espresso. This is done in order to increase coffee's surface area. This should increase extraction yield. The extraction yield is the percentage of soluble solids that are dissolved and end up in the final beverage.

How Grind Size Affects Surface Area

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. Low extraction yields taste bitter and higher yields are more flavorful.

They made thousands of espresso shots. Then they developed a mathematical formula to identify the variables that are required to produce consistent yield. The team discovered that coffee ground too fine can cause a restricted flow and over-extracted shots.

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

The problem lies in the size of coffee particles. An example is the comparison of sand and rock. You have the same weight. You can pour water onto the rocks and it will instantly pass through. You can pour the same amount over the sand but it may take a little longer to get through the layer.

The other part of the 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.

Researchers discovered that a coarser coffee grind and a lower amount of ground coffee per cup is better. This results in a more full and even brewing process.

The Other Extreme

Finer coffee is also problematic. The only thing you need to adjust is the grind size. These changes are not noticeable to the naked eye.

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. This would be way too fast, and it would only extract the acids. You will find that your coffee is very under-extracted.

Espresso Variables & Extraction

The roast degree can have an effect on extraction, but it is not a determining factor. It'll extract coffee beans more efficiently if they are roasted at a darker roast than if they are roasted at a lighter temperature.

A double dose of coffee should not exceed 14 grams. You want to get the best possible results so that the cup weighs no more than one gram.

Tamping will affect the flow rate of your coffee, which in turn impacts how much of the ground coffee is extracted.

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 too strict

Coffee brewing is a creative process.

The human component of coffee is what makes it so special and why people love it. While it is important that we can make decisions about flavor, the scientific component of coffee allows us also to make decisions for improving our coffee. Creativity and personal taste are equally important.

This article was syndicated from Daily Preston UK News.