Pressure profiling in espresso machines has been a topic that has been around for a very long time. The traditional spring-loaded lever espresso machines had their unique pressure profile. Some of the modern day espresso machine manufacturers have also applied their own standard pressure profiles to their machines with a few of them giving the barista the ability to change pressure during the extraction process. On the other hand, even though the concept of flow rate profiling has been around for some time, flow rate profiling is not a common phrase used among baristas. Only a handful, or less, of espresso machine manufacturers actually allow the barista to change the flow rate during extraction. So what is the difference?
Pressure is the force produced by the pump that will push water into the grouphead. Flow rate is the amount of water that passes through the grouphead in a given amount of time. Majority of espresso machines are set to produce 9 bars of pressure at the pump. But this does not mean that the pressure on the coffee puck is 9 bars. The pressure at the coffee puck can change due to resistance naturally created in the grouphead. For example, a finer grind will create more resistance and increase the pressure in the grouphead than when using a coarser grind. Inversely, when pressure increases in the grouphead, the flow rate will decrease. This means that less water is going through the coffee puck within a given amount of time.
So which is more important? Flow rate is what we are interested in as it is the contact between the coffee and water that gives us extraction. As contact time between coffee and water in the espresso machine is a major factor that will affect extraction, flow rate information (and control) will help us to get better extractions. Especially if we consider that majority of espresso machines are measuring pressure at the pump and not in the grouphead, pressure information becomes more distant in relation to our extraction.
Flow rate profiling may be something that you have never considered before. But if you have been wondering about pressure profiling, it is much more crucial to look at flow rate profiling. As more and more espresso machine manufacturers are implementing flow rate within their parameters of control, flow rate profiling may be closer than you think.
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