Tennisfox Said:

My Tea will max at about 10.5 but when the heater turns back on, the pressure drops to about 6.  I also notice that when grinding, the grinder will slow down when the boiler turns back on.  Is this normal, or do I not have enough power to feed my machine?

Lew

Posted March 3, 2004 link

daktarz Said:

When I got my Rituale back from Chris' Coffee I noticed that the pressure had been set so that it went to 11 bar and sometimes even a touch higher during a pull. This is at variance with all I've read vis a vis the proper pressure. Before tweaking it myself I called and spoke with one of their techs (the guy who worked on my machine). What he told me was that he did indeed set it to 11 bar and explained that 9-10 bar is correct for rotary pumps but that vibratory pumps (such as the ones in the Isomacs) wouldn't pull consistent shots unless set higher. Hence the 11 bars. This is the first I've ever heard of such a thing, although it may well be that the 9-10 bar recommendation always has a rotary pump implicitly in mind. Anyone knowledgable about the subject care to weigh in?

Posted March 2, 2004 link

1. The technician saying that one knows the grind and tamp are correct if one is seeing 9 bar is spewing nonsense. What about singles, or ristrettos? The grind and tamp are right if the espresso tastes sweet and neither sour nor bitter; having to worry about pump pressure on top of this is ridiculous.
   
   
2. Illy claims 11 bar is best for pods. The 11 bar setting on vibe pumps is also a factory tradition. So is marketing departments claiming 15, 18, or God knows how many bar for their espressos.  If you're pulling shots from some  flat, stale 90% Brazilian "genuine Italian" espresso blend; 11 bar may be great for all I know.
   
   
3. But published taste tests consistently show that for fresh coffee 7 to 9 bar is preferred, since 11 bar overextracts and produces excess bitterness, especially in longer singles. My experience after several months of side by side tests confirms this. I prefer about 8.5 bar for my shots. This is almost identical to the pressure settings used at Intelligentsia and recommended by Schomer and Dr John (of Malabar Gold fame). The file is too large to attach, so you can find it here in the espresso research folder.
   
   

another_jim Said:

There's a few threads on this:

First off, pressure in vibe pumps is inversely related to flow. At 2 ounces in 25 seconds you'll be around 9 bar in any case, even if the relief valve is set higher; but singles and ristrettos will pull higher.
And as always, don't ask me, don't ask anyone else, taste it for yourself!

Posted March 5, 2004 link