GlennV wrote:Isn't extraction higher because the contact time is increased? The same amount of water is going through the puck, but taking longer to do so. Or, looking at it another way, each slug of water is spending more time at each layer of the puck.
I think this is formally called 'diffusion'. I have always found it odd that this is never given much air play when it comes to espresso extraction. It perhaps gives a clue on some of the lever techniques where extraction time for a standard brew ratio can go on for significantly longer but without a significant impact on espresso quality.
How this all relates to the 'extraction within 20 secs' concept as well as grind fineness is probably a subject for another thread.