Espresso should be grind to a fine point however, not too delicate. Espresso making has been difficult to master over the years. Even the most skilled baristas make mistakes from time to occasion. The problem is even more severe if you're using a superautomatic.
The one thing that remains constant is the grind size is the same for espresso will vary. The perfect grind size is vital for a shot with a hint of sweetness but not overly bitter.
Espresso Extraction
Roasted coffee beans contain around 28 percent water-soluble. This means that you can extract approximately 28% from the whole coffee bean. The remainder is mostly plant material that form the coffee bean's structure.
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Water needs help to dissolve soluble chemicals. Coffee beans can dissolve only if they are cooked in hot water. The structure of the coffee bean is extremely complex and dense and water is unable to move through it easily. The water is able to hold every flavor.
Coffee tastes better when there is enhance the bean's surface. Doing this will create gaps that allow water to permeate all the taste. Coffee beans can be crushed to increase their surface area. The larger the surface area is increased, the faster the reaction to water.
Water extracts flavor compounds in the following order regardless of how it is created acids, fats sugars, acids, and fats, followed by plant fibers.
There are a few coffees whose tastes are great, so we must control the extraction process and stop it when the bitter compounds start to break down. We don't want the entire insoluble matter to be absorbed into our coffee. A large portion of those substances are undesirable, and we'd like to avoid removing those.
Fortunately, chemistry works with us on this, because most of the bitter compounds are more difficult to extract, and if we stop extraction at the right time and only extract the best substance.
Under Extraction
The cup you get will be with too little soluble solids in the ground coffee. Many of the flavors that balance your drink remain unextracted from the ground. Acids are the best extractors of compounds, so an unextracted shot might taste a bit salty, bitter and devoid of sweetness.
The extraction of coffee is directly linked to its strength. If you are looking for a powerful coffee, you may utilize less water to boost the strength of the cup. Not the best idea but it's feasible. It's harder to extract the full flavor of coffee the more you drink it. The brew is saturated with Saturates. The most important thing is the fact that coffee's components are different in their saturation levels , so we can extract more of them during making. This is why when we brew a drip coffee to the strength of espresso, it can taste bitter.
The thing that is interesting is that a group consisting of baristas, roasters and researchers studied the extraction of coffee and discovered that grinding too finely does not result in the best tasting cup.
The Size of the Grind and Extraction
A pressure pump is utilized to push water into the "puck" of ground espresso. This makes a delicious and intense cup of coffee.
A popular recipe for espresso is extra-fine grind settings around 20 grams for brewing a single espresso shot. This helps increase the coffee's surface area, which is then converted to water. This should result in a more efficient extraction yield. Extraction yield is measured by the amount of solids that are soluble and end up in the final beverage.
How Grinder Size Affects Surface Area
A study conducted by the University of Oregon led by Christopher Hendon , computer scientist, and an experienced barista, found that most coffee shops aim to achieve an extraction yield of 17 and 23 percent. Higher extraction yields can taste bitter, while lower yields can make you feel sour.
The team prepared hundreds of espresso shots and came up with a mathematical formula to determine the factors needed to get an even yield. They observed that when coffee is ground to fine, the flow of coffee is sometimes restricted, and the shot is over-extracted.
If you've have ever ground your coffee to fine, you'll notice this. Water simply won't flow through the coffee grinds if the grounds are too fine. Water can't pass through ground coffee that is tightly packed because the puck is too small.
The issue lies in the size of coffee particles. A good analogy would be the contrast between rocks and sand. The same amount of sand is available in terms of weight. It is possible to pour water over the rocks and it will instantly flow through. It may take a few minutes to allow the water to pass through the sand layer If you pour the exact amount of water on the rocks.
The other aspect of the issue is tapping. You can pack finely ground coffee more easily and the puck will become much smaller if you tap it. This restricts the flow even further, if you tamp too difficult.
The study team found that using a slightly more coarse grind, and reducing the amount of ground coffee per shot is better. This will leave more room in the coffee bed, leading to a fuller and more evenly brewed process.
The Other Extreme
However, the coarser variety of coffee is exactly the same as the finer ones. The only thing you need is a few adjustments to the grind size, these adjustments are not noticeable to the naked eye.
Let's look at an extreme case that if you make an espresso shot a medium grind, what is commonly used to prepare a drip coffee, your espresso will be ready in three seconds. It's way too fast, and it will only extract acids. This could cause your coffee to be very under-extracted.
Espresso Variables and Extraction
The roasting temperature can have an effect on extraction, however it's not the sole factor. A coffee bean is more efficient in extraction when it's dark roast , in contrast to lighter roasts.
A double shot of coffee should be between 14 to 21 grams. To achieve the best results, ensure that the quantity is within 1 gram of number on the container.
Tamping can alter the flow rate of your coffee which can affect the quantity of coffee you get.
Grinder fines are beneficial because they can block the puck and help in flow. The coffee grounds and water have a contact time of 20 minutes. However, too much finesse can clog the puck too much and the shot may simply not flow.
Do not be too strict.
Coffee can be a creative process.
One of the wonderful things about the industry, and why people like coffee, is because there's an element of human that you can't eliminate. It's the scientific component that lets us make choices about flavor. It can be used to enhance our coffee. But creativity and personal flavor are equally important.