Received wisdom about brew pressure

Want to talk espresso but not sure which forum? If so, this is the right one.
User avatar
another_jim
Team HB

#1: Post by another_jim »

There's two disputable assertions on lever groups - that they have greater clarity and less crema, and that the reason is lack of vibration.

The first is an oft repeated observation -- I get it reliably and invariably when I set the La Peppina and Tea side by side, Mark mentions it in the Elektra review. Almost all owners of lever machines, home or commercial attest to it. Obviously, it could be wrong, but it's about as solid as any other fact in this game.

The reason for it being lack of vibration is mostly unresearched. I was the one who raised the pressure profile as an altrnative possibility; and, so far, am the only person I know of who's tried it. Most people just don't have big variacs lying around into which they can plug their machines or pumps. of course, even modified the E61's profile has the 10 second ramp up, so that's still a point of difference to the typical lever having a no pressure presoak for around the same length of time.

...

Thinking about this. I guess there's a lot of received wisdom about pressure, most of it virtually untested, and perhaps wrong. The knowledge about temperature variations is hugely more reliable, since adjusting temps is a part of lots of people's daily shot making practice. Adjusting pressure is usually done for maintenance or gross defects, not taste adjustments. So there's several orders of magnitude less data on it.

User avatar
HB
Admin

#2: Post by HB »

another_jim wrote:of course, even modified the E61's profile has the 10 second ramp up, so that's still a point of difference to the typical lever having a no pressure presoak for around the same length of time.
Not only does a spring lever's pressure start at ~one bar for the presoak and then rocket to 9 bar in less than a second, the temperature also shoots straight up faster than anything I've measured, returning us to the age-old question of the effects of temperature profiles. A convincing experiment to determine the effects of vibration would be a rotary pump versus an air pressure-driven water chamber. I recall someone saying the new Techno had such a beast, but I didn't check it out at the SCAA conference.

However, I don't know that I'd feel very comfy with such a pressurized chamber sitting on my countertop. In the meantime, you can label hypotheses where necessary as you suggested earlier.

Image
Dan Kehn

User avatar
another_jim
Team HB

#3: Post by another_jim »

That's a fast ramp up, and a dramatic ramp down. I didn't notice that on the La Peppina. How'd the shot taste?

User avatar
malachi

#4: Post by malachi »

other possible explanations (devils advocate time) would include the gravity pressure pre-infusion and the different temp profile as well as the interaction between either or both of these and the different pressure profile.

in other words... i'd hesitate to say that vibration is the cause of either of these observed attributes - much less both.

User avatar
HB
Admin

#5: Post by HB »

Jim,

I only had the Cremina for a week and didn't TC meter each shot, so I won't swear the one I posted is correct. However, it was the third and final shot, so the group was pretty hot. The curve was what I expected to see, otherwise I would have checked further.

The taste was exactly as you described "purer and more transparent, with less bitterness and acridity than otherwise identical shots from motor pump machines." I've commented to coffee friends that an espresso served from the Microcasa isn't easily recognized as the same blend from an E61 / vibe pump machine. In addition to the clarity we've ascribed to spring lever machines, I also like in particular how the roast notes drop off in Black Cat, enhancing the intense chocolate-y flavor.

The effect is unquestionably real. Like Chris, I'm not certain about the cause. There's other significant variables we're not controlling in these side-by-side tests (yet).
Dan Kehn

User avatar
another_jim
Team HB

#6: Post by another_jim »

Doh! It's the group shedding heat during the shot. I always thought most of the heat would be lost as the cylinder filled, but I guess it's still cooling off during the shot.