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How Grind Size Affects Espresso Extraction

Jan 6

Espresso should not be too fine. Espresso making has been difficult to master for many years. Even the most skilled baristas can make mistakes. Even worse is if you have a super-automatic.

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

Espresso Extraction

About 28% of roasted coffee beans is water-soluble. You can extract around 28% of the whole roasted coffee beans. The rest is cellulose, plant matter and other materials that form the coffee bean’s structure.

Water needs help to dissolve soluble chemicals. You can only dissolve the outer layer of coffee beans by boiling them in hot water. The structure of the coffee bean is extremely dense and complex. Water can't penetrate it easily. All the flavor is collected by the water on its way through.

The bean's surface area must be increased to make coffee more flavorful. This will result in gaps that let water through to the coffee, which allows for all its flavor. By grinding coffee beans, we can increase the coffee bean's surface area. 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 were the first compounds that coffee can be extracted. Acids, which give coffee a bitter taste, are the easiest compounds to extract. It's easy to dissolve them in coffee water. Many of the light aromatics, for instance the the floral an d the fruity flavors are extracted at this moment. Our final cup should contain both acidic and light flavors. This is what 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 of the soluble matter to be in our cup. We don't want any of those compounds to be in our cup.

Chemistry can help us with this because most bitter compounds are difficult to extract. Therefore, if we stop extracting in time, we will 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

The result of not extracting enough soluble solids out of the ground coffee is a cup that's under-extracted. Many of the flavors that add balance to your shot are not extracted 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.

The extraction of coffee is directly related to the strength. You can use less water to make a stronger cup. Not the best idea, though possible. The more coffee you extract, the more difficult it is to extract out all of the good flavors. The brew will saturate. 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. Grind size is the most important variable for 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 grinder settings are 20 grams for a single shot espresso. The reason is to increase the coffee's surface area to water. This should increase extraction yield. The amount of soluble liquids that dissolve in the final beverage is called extraction yield.

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. 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. They found that coffee that is too finely ground can result in too much extraction.

Don't grind your coffee any finer than necessary. Water just doesn't pass through the coffee grinds, if the grounds are too fine. The puck is too compact, and water will not pass through the densely packed coffee grounds.

Coffee particle size is a major problem. A good analogy is the comparison between sand and rocks. The same amount of sand and rocks is equal in weight. When you pour water on the rocks, it will immediately pass through. If you pour the same quantity over the sand, it will take a bit of time to pass through the layer of sand.

Tampering is another issue. When you tamp very finely ground coffee, you can pack it better, so the coffee puck is more compact. If you tamp too hard, this can reduce the flow.

Researchers discovered that a coarser coffee grind and a lower amount of ground coffee per cup is better. This gives you more space in your coffee bed which leads to a better brewing process.

The Other Extreme

Finer coffee can also be problematic. Only very minor adjustments are needed in 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. This would only extract the acids. The coffee will be severely under-extracted.

Espresso Variables, and Espresso Extraction

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 weigh between 11.5 and 21 grams. For best results, try to keep the measurement within one gram of the number on the container.

Tamping can alter the flow rate and therefore the amount of coffee that 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 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'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.