Scientists have finally answered a burning question of mine: why should an espresso be brewed in 25 +/- 2 seconds and use approx 15-22gr of dry coffee to yield 50ml of (a double) espresso?
Who came up with this rule and why? Not that I have a specific problem with it but it seems so arbitrary. Also, once you start to make espresso’s a day long, you’ll notice that it’s really hard to dial in the equipment a certain way and maintain those rules for every cup. Sometimes it’ll be 21 seconds, sometimes 29. The grinder is pretty accurate. The beans are practically the same. So where does this high variation come from?
Well, it turns out that brewing your espresso differently yields the same great taste and flavors while achieving this with much greater consistency and reducing the cost per cup of espresso!
How did they do it? Well, they started by reducing the process to a proper model with solid mathematics behind it. Brewing an espresso is basically fluid dynamics of a bed of particles. The “puck” being coffee grinds of varying sizes and water is pushed through this bed at a certain pressure.
These mathematics are very well understood and accepted. So the scientists started with this model, created equations for everything and solved the equations using differential equations. That resulted in a few parameters and then they found the optimal solutions.
Sounds easy enough but believe me the math is pretty impressive, yet their logic is sound.
Turns out if you lower the pressure to 6 bars instead of 9, use 7-15gr of dry coffee, ground more coarse then tradition tells you to and aim for an extraction of 8-15 seconds, you will get a beautiful espresso that is much easier to reproduce!
Don’t believe it? Read the articles:
No Pressure Coffee 