Markarian Senior Member Joined: 27 Jun 2012 Posts: 658 Location: Seattle Area Expertise: I love coffee
Espresso: ECM Technika IV Profi WT-WC Grinder: Baratza Forte AP, HG One Vac Pot: Bunn Trifecta MB Drip: Moka, Aeropress, Hario V60 Roaster: Behmor 1600
Posted Thu Feb 28, 2013, 5:35pm Subject: Preinfusion: How do I get the most out of it?
Okay, so there were a few threads over the years, debating whether or not the Oscar has true preinfusion. I don't know what it technically has, but I do know that the brew button is a two-stage switch, that when depressed, opens the 3-way valve and starts the pump, in that order. If you feather the button just so, you can open the valve without activating the pump, letting the HX gently drain from the group. Should I ever use this "feature" and if so, how would I go about it and when would it be best called for.
It evenly wets the coffee, increasing the likelihood that you'll get an even extraction without "channeling."
It sets up the physical structure of the puck so, without changing anything else, one gets a faster flow rate during the high pressure extraction phase.
Speculation is that effect #2 occurs because the coffee particles swell, locking fine particles into the puck matrix before the subsequent high pressure phase has a chance to wash them downwards,into a restricting layer at the puck's base.
A preinfusion-aided, faster flow rate means one can grind finer. This finer grind enables you to properly extract coffees that are otherwise hard to extract (ie, the light-roasted third wave style). Without preinfusion they tend to underextract and can be sour or exhibit a dry tartness. They sometimes taste bitter. With preinfusion more of the sweet compounds come out. This gives balance to an otherwise unpleasing shot.
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