Bezzera Strega - Second Look - Page 25

Behind the scenes of the site's upcoming equipment reviews.
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Carneiro
Supporter ♡

Postby Carneiro » Feb 28, 2012, 9:28 pm

Lower (declining) flow rate?

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another_jim
Team HB

Postby another_jim » Feb 28, 2012, 9:38 pm

The shots are a five to ten seconds slower, but the flow is also lower -- I always thought that would be a wash in terms of extraction.
Jim Schulman

GlennV

Postby GlennV » Feb 29, 2012, 5:56 pm

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.

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another_jim
Team HB

Postby another_jim » Feb 29, 2012, 6:16 pm

That's probably it: the increased time trumps the decreased pressure.

Maybe that's the real secret of levers ... Perhaps high pressure is only needed at the start of an espresso shot, to set up the puck and get the crema going; after that it may no longer be necessary.
Jim Schulman

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shadowfax

Postby shadowfax » Feb 29, 2012, 7:16 pm

another_jim wrote:after that it may no longer be necessary.

Or: after the initial stages it's more of a tool to modulate shot volume without effecting extraction as much, i.e. the higher the pressure later in the shot, the more liquid is forced through in a given time, all other things being equal.
Nicholas Lundgaard

ziobeege_72

Postby ziobeege_72 » Mar 14, 2012, 12:43 pm

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.