Espresso extraction time and area the most standard time and pressure of espresso extraction

In this article, I will talk about how to increase and decrease the extraction of coffee from a theoretical level.

Angela Grieve, a Hustle subscriber, emailed me about this question, so Angela, there should be the answer you are looking for in this article!

There are several variables that can be adjusted for extraction, the two most important of which are extraction time and extraction area. In any way of cooking, these two variables are closely related and inseparable, and you can't change one variable without touching the other.

Extraction time (Time)

If you increase the contact time between water and coffee powder, more flavor substances will be extracted. If the water comes into contact with the coffee long enough, the extraction will continue until no more is dissolved. All we have to do is to find out when the extraction reaches the best flavor value.

With regard to the variable of extraction time, there are actually two different aspects that need to be considered separately. The first point is what water can extract and when to start extraction, which basically depends on the contact time between water and coffee powder; the second point is whether water can successfully extract flavor substances from coffee powder, which is related to both the extraction time and the extraction area, so I will analyze it later.

What can water extract? when does the extraction start?

The soluble ingredients in coffee will all have different solubility (this may sound strange, but follow my way of thinking). Salts, sugars, acids, phenols, fats and lipids all take different times to dissolve into water. Some begin to dissolve as soon as the water comes into contact with coffee powder, while others may have to wait a little longer. We need to take these situations into account when brewing coffee, because changing the contact time between water and coffee will affect the amount of soluble matter that is dissolved. The easiest and first parts of coffee to be dissolved are fruit acids and organic salts (which bring light and bright fruit flavors); this is followed by light aromatic substances produced by the Mena reaction and caramel reactions (flavors such as nuts, caramel, vanilla, chocolate, butter, etc.); and finally, heavy organic matter (bringing wood, ash, malt, tobacco, etc.).

The most common mistake people make is too short extraction, because most coffee lovers who are reading this article are not very receptive to gray or bitter taste. Unfortunately, too short extraction is likely to sacrifice sweetness. Coffee, as always, always asks us to make compromises.

Extraction area (Surface Area)

Increasing the contact area between coffee and water makes it easier for water to extract flavor substances. When you grind the coffee into powder, the surface area of the coffee increases exponentially.

You can think of coffee beans as a cube with a side length of 1cm, with six faces, each with an area of 1cm2, so the surface area of this cube is 6cm2.

Cut the cube in half and then in half. Until you get eight small cubes. At this time, the side length of each small cube is 0.5cm, the surface area is 1.5cm2, the total area of these eight small cubes will be 12cm2, and the surface area that water can contact increases. It didn't take long for us to double the extraction area.

Then let these small cubes undergo a rough grinding to get 64 small cubes with side length of 0.25cm. The surface area of a single small cube is 0.375cm2, and the total surface area becomes 24cm2. It's doubled again!

In the usual Italian grinding case, the cube of 1cm will be crushed into hundreds of small particles, and you should be able to imagine how the extraction area of coffee will be multiplied. With the rapid increase in the surface area of coffee extraction, it becomes easier for water to dissolve most of the flavor substances in coffee. That's enough. I'm not going to draw you another 1024 little cubes.

In these hypothetical small cubes, there are a large number of flavor substances that can not be immediately touched by water. This is why thicker coffee powders take more time to extract than finer ones: it takes some time for water to get inside these thicker coffee powders, which are then dissolved and transported to external solvents. When it comes to fine powders, all the water has to do is touch them, and everything will be dissolved. With this comparison, you should be able to understand how important the extraction area is in increasing extraction.

The most important thing I want to tell you here is that the thickness of coffee powder does not change the substance being extracted. The only thing it does change is when these substances are extracted. All the flavor substances are there from beginning to end, and they have been preserved in coffee beans waiting to be extracted. Grinding finer or thicker just allows water to come into contact with more or less flavor substances in the first place.

We can also think differently about the extraction area: when we think about how to adjust the grinding degree, we are actually thinking about "how many coffee flavor substances do you want to hide away from water contact?" or "what percentage of flavor substances do you want to be delayed?" The finer powder can hide less flavor, which will reduce the delay effect, while the thicker powder will hide more flavor substances and enhance the delay effect.

When you want to increase the extraction, you grind the powder finer, which increases the extraction area of the coffee powder and exposes more of the coffee flavor to the water. When you make this adjustment, your extraction will be improved because water can capture more flavor substances and dissolve them more quickly.

Remember: all the flavor substances are always in the coffee powder waiting to be extracted, and the purpose of increasing or decreasing the surface area of the coffee powder is to bring them closer to or further away from water.

How easy will it be to extract water?

If there are many coarse powders, it will be difficult for water to enter the interior of these powders to dissolve flavor substances. Water needs to pass through an intricate maze of cellulosic tissue to reach the flavor substance and come into contact with it for a certain period of time to dissolve what we need (as mentioned above). The water then brings the dissolved substance to the solvent outside the coffee powder. Coarse powder will require relatively more contact time, this is because it takes more time to complete these three steps. For example, stage (1) the extraction of outer substances takes 1 unit time, and stage (2) water enters and comes into contact with most flavor substances, it takes 1 unit time Stage (3) it takes 1 unit of time for the water to bring out the dissolved flavor, and if the flavor is hidden in the depths of the large coffee particles, it may take three times as long to extract it, but in the process, the outer part of the coffee is still being extracted, and it is likely to be far beyond your expectations.

What does all this mean for Espresso?

When you make Espresso, you only have about 30 seconds to extract, which means that those large coffee particles are actually useless "fillers" that cannot be extracted thoroughly or evenly. Espresso coffee powder particles are usually very small so that water can extract enough flavor substances in a short period of time. You may have seen my 2013 WBC game, in which I will be better known for the way I applied Mahlkonig EK43 to Espresso extraction (which I didn't invent). It is very important to use EK43 or other similar flat knife grinding when making Espresso, because the particle size distribution of the powder is more uniform, thus ensuring the consistency of most (or even all) flavor substances in contact with water in such a short extraction time.

Don't worry, there will be more about this in Hustle in the future.

What does it mean for filtered coffee?

We use much thicker powder when making filtered coffee (such as French pressure or hand-brewing), and the reason for this is mainly related to the contact time of gouache. The extraction time of filtered coffee is much longer than that of Espresso, because the extraction of filtered coffee mainly depends on the gravity of the water itself, and the speed of water passing through the coffee powder is much slower than that in which the Italian coffee machine relies on a water pump to provide high pressure so that water can penetrate the coffee powder and filter bowl in a short time. Because the extraction time is longer, when making filtered coffee, we should hide the flavor substances in the particles as much as possible to avoid excessive extraction.

It is important to keep in mind that while you are waiting for the flavor substances inside the larger particles to be extracted, the smaller particles are still being extracted and will not stop. So you need to decide-is waiting really good for you to get more extraction from these large particles (yes, I'm talking about sweetness), or does waiting allow small particles to be overextracted (bitter and dry)? Make a wise decision!

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