That is a good point that I should have written in the conclusion. Having the correct bar pressure is crucial for extracting the best flavour from your coffee.
The higher extractions could have been a result of slower flow rates and longer contact times instead of a more even extraction.I'd be a little cautious on distinguishing the difference between pressure and flow as it relates to coffee extraction. The reason why I say this is because we are not the only ones who have discovered that the optimal espresso brew pressure lies below 9 bars, where optimal is defined as ideal for even and higher extractions instead of speed.Other coffee professionals like Scott Rao, Matt Perger from St. Ali, Socratic Coffee and numerous others have had similar findings within their own research. As most baristas and espresso lovers know, professional machines are set to brew coffee at 9-bar of pressure, while home or semi-professional machines are often quoted to have around 15-bar. How the coffee tastes will have more to do with the selected disc rather than the brewing process. With the optimal brewing temperature being 200 degrees Fahrenheit (93.3 degrees Celsius), and the point at which water turn being hotter than that, the resulting coffee will taste burnt and over-extracted.With a pump or rotary driven espresso machine, this is not the case. Between 9 and 15 bars is the perfect pressure for full-flavoured coffee with a professional crema. I use the coffee only for three weeks and then discard it.I have found that 7 to 8 bars of pressure give me the best crema and the best flavor profiles from any and all coffees. A worn pump may be unable to regulate the pressure originally set and this needs to be serviced or replaced. This is essential for steam to meet the coffee granules at the right speed; too slow and it can result in bitter espresso.
In tests, the espresso was rich but with only a hint of crema, while the hot chocolate was indulgent and frothy. The point of publishing is for peers to review and improve it to the point where it is sufficiently valuable for our audience to make use of the information within their work.Hey Chas,I'm glad you enjoyed the article :) There is loads more to research in this area of course. But the extraction times were not constant as we lowered the brew pressure. Many espresso machines have a gauge that shows the pressure of the machine. If you have just run water from a group the pressure will climb above brew pressure as the cold water that has just entered the boiler increases in temperature, expands and therefore increases boiler pressure. To measure the pressure at the grouphead, we need to use a tool called the Scace. Once that temperature is reached, it is pumped through with great force with the rotary motor or pump, pulling perfect espresso shots in the process. We've run a number of other experiments but haven't published just because it is extremely time-consuming to write about them.You are correct to say that there are other variables that contribute to the optimal brew pressure, the key variable among them being distribution of grinds in the portafilter. However, this may be different for a few reasons.
Cheaper machines will also deteriorate more quickly and the bar pressure will drop over time as components wear out.The short answer is that no, anything over 10 bars won’t really increase the quality of espresso. If professional coffee is made with 9 bar, then why do home machines work with 15 bar? Did you adjust the grind setting when lowering the pressure?
Hi Ian, thank you for your comment! I think the takeaway from the experiment should be the higher consistency with lower brewing pressures. Which bar pressure espresso machine When shopping for an espresso machine, among the millions of features advertised is the bar pressure rating of the machine, meaning how much pressure is used to force the water through the coffee grounds in the portafilter. Some baristi deliberately adjust the brew pressure to control espresso extraction. Watch the video below to find out more about what espresso bar pressure means.9-bar (at the brew head) is always the aim.
If the machine is setup correctly the brew head pressure will be around the perfect 9-bar mark, regardless of what pressure the pump creates.
Even if you increased the pressure astronomically, drinking a 12-second espresso shot is not going to be a good experience.