In this seventh post of the coffee extraction parameter series, we will look in to pressure. Please check this series summary page as well.
When we think about pressure in terms of coffee, I believe most will think about espresso. This style of coffee uses very high pressures during the extraction to extract coffee in to a very small amount of liquid in a very short period of time. Pressure is used as the energy to boost the extraction level. From this you get a very concentrated strong coffee.
There are some other brewers which aim to replicate this high pressure at a lower cost. A mocha pot is a popular choice. There are other brewers which do this too, but many cannot reach the necessary levels of pressure for “real espresso”, as people like to call them.
Crema is the layer of foam which forms on top of espresso. This is kind of a bi-product of the high pressures used. When the pressurized water contacts the bed of coffee in an espresso machine, the CO2 gas contained in the coffee dissolves in to the water. Since water can dissolve more gas at high pressures, during the extraction phase a lot of CO2 gas is dissolved. But the moment the coffee leaves the pressurized brew chamber, the pressure decreases on the coffee. At this point the coffee cannot sustain the high levels of CO2 dissolved in it, so it lets the gas escape as bubbles. These tiny bubbles that form in the coffee, give you the crema.
Since the formation of crema is directly linked to the level of pressure applied, it is often used to distinguish between “true espresso” an espresso-like drink. Espresso machines typically use pressures around 9bars.
Crema just looks awesome and gives a great texture to the espresso, but apparently it does not taste so good on its own.
It goes without saying but you will never be able to apply pressure to your pour-over coffee. Controlling this parameter largely depends on your brewer. And typically it is pretty difficult to adjust pressures.
This post concludes the 7 part series on coffee extraction parameters.
There are countless ways to brew coffee, and by adjusting some extraction parameters, you can greatly affect the end result. The skill of adjusting these parameters will lead you to the best cup of coffee for you.
I very much hope that this series helps you in improving this skill.
Links to other post in the series
The other parameters are discussed in these other posts.