What makes an espresso, well, an espresso? The pressure. Of course, there is also the cream, the size of the drink and the concentrated nature of the coffee, but in the end, it all comes down to pressure.
But why is it so important? How does it affect espresso recipes? And why 9 bars is often the recommended amount of pressure?
I had a lot of questions about the pressure, so I spoke with Stephen Kim of Cafflano to find the answers. Cafflano, which has already won awards for its manual coffee makers, Klassic and Kompact, is about to launch with the first manual espresso machine capable of holding 9 pressure bars throughout the process. Who better to explain to me about the pressure in espresso?
Pressure 101
The pressure is measured in barometric pressure (also known as atmospheric pressure). This is the force exerted by the atmosphere. Basically, it is the weight of air at sea level.
When making espresso, you will generally want 9 bars of pressure or 9 times the weight of pressure at sea level. "The espresso has a long history, and 9 bars are known to be the optimum pressure used to extract the best espresso," Stephen tells me.
To get some perspective on this, think about pumping the car or bicycle tire. Most car tires specify that you should pump them up to 32 PSI, pounds per square inch, while on bicycles it can go as high as 65-85 PSI.
9 bars, however. It is the equivalent of 130 PSI - More than 4 times more than a car tire.
Pressure Control
Imagine taking a high-pressure hose and pumping a stream of water at 130 PSI through your ground coffee. This would make a disaster. This means that we need to control the way those 9 pressure bars are applied - which brings us to the heart of espresso theory.
How do we handle the pressure? By forming an espresso bar and controlling the time to extract coffee.
Let's take a look first at the pill. To avoid that disaster mentioned above, we need something that offers resistance to water that is pressed through the coffee particles.
So first of all, we make sure that the grinding size of the coffee is very fine. Any coffee can be used to make espresso, but it has to be finely ground and then compacted in a filter holder, creating a tablet or disk. This results in a dense and uniform surface that will offer water resistance.
Now let's look at the time, which is a bit more complex.
Settings for Coffee Flavor Profiles
Although the exact times vary, it usually takes 25-30 seconds to extract an espresso shot - if you are using 9 bars -. Less pressure and it will take longer; More pressure, and it will take less time.
It is a bit more complicated than this because coffee also needs time to extract properly. Even if you increase the pressure excessively, drinking a 12-second espresso is not going to be a good experience.
The exact amount of time required for extraction depends on many factors: grinding size, coffee itself, water temperature, extraction, and personal preferences. And as we have already said, we have very little flexibility with the size of the grind.
This means that dose, extraction and time are your main variables for espresso recipes (unless you have access to a professional espresso machine that can control the pressure and/or water temperature).
There are some people who also like to vary the pressure: starting with low pressure for preinfusion before raising it to 9 bars, and then the decreasing pressure to coincide towards the end. Maxwell Colonna-Dashwood has advocated the use of 6 pressure bars. As always, with coffee, there are more things to learn and our ideas about extraction are constantly evolving
However, for now, 9 bars remain the benchmark. In fact, controlling pressure is something that can only be achieved in high-end espresso machines with pressure profile capabilities.
Why would you want to adjust variables such as grind size and water temperature? Take light and medium roasting as an example. Roasting degrades the cellular structure of coffee beans, making them more soluble. Light roasts, being roasted less time, are in turn less soluble. This can lead to under - extraction - that is, a more sour, almost bitter, taste profile - unless the recipe is manipulated to match. (This is the reason why many roasters create “ espresso roasts ”, which are darker than their filter counterparts).
So, let's summarize: there are plenty of ways to manipulate espresso recipes, including changing preparation time, grind size, water temperature, pressure, and more. But for espresso, you'll want a fine grind, and 9 bars is generally considered the magic number for pressure. This, in turn, dictates a time of 25-30 seconds.
Of course, there are also many other aspects that are key to a great espresso: the compacting, the roasting date of the coffee, the dose of coffee, the density of the grain, the quality of the equipment, the size of the basket of the filter holder, the water hardness, room temperature ... But these are topics for other items.
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