Bezzera Strega - Second Look - Page 25

Behind the scenes of the site's projects and equipment reviews.
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Carneiro
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#241: Post by Carneiro »

Lower (declining) flow rate?

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another_jim
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#242: Post by another_jim »

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
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#243: Post by GlennV »

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
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#244: Post by another_jim »

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
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#245: Post by shadowfax »

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
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#246: Post by ziobeege_72 »

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.

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