HB wrote:The incoming port is cut off by the piston through most of its stroke. In the case of the Microcasa, the area above the piston is open to the outside. You can see the upper hole in this photo:

Yes, i know, it's exactly like my Pavoni , there are 2 port. I will explain better what i think (sorry, english it's not my language):
Suppose to cut off the port and soon after leave the lever in a Pavoni machine (without any spring). It will not move because the pressure under the piston (in the coffee puck) is equal to that above the piston (boiler pressure), hence the pressure on the coffee is 1bar without any force applied to the lever. All the force that you will make afterwards it will be added to that 1bar pressure initially generated by the boiler.

HB wrote:shown above. It has the added benefit of allowing the barista to quickly heat the group with short up/down strokes, which pulls water in/out of the boiler (a trick pointed out to me by LMWDP founder Steve Robinson).

I always make it on my Pavoni millenium.

Dan, from what you say am i right to assume the boiler pressure is effective to the point the port is cut off (Achille aside). Given a 15 sec pull on the Europiccola I think the port would be cut off at around 3 seconds

Alchemist came up with that pull pressure mod and provided a curve that led him wonder about a dip shortly into the pull, i wonder if this might be associated to the piston cutting off the water port...

http://www.home-barista.com/forum...2356-20.html#22815

pab wrote:Suppose to cut off the port and soon after leave the lever in a Pavoni machine (without any spring). It will not move because the pressure under the piston (in the coffee puck) is equal to that above the piston (boiler pressure), hence the pressure on the coffee is 1bar without any force applied to the lever.

Pab, what lets you conclude the existence of boiler pressure since the port is cut off? I'd rather tend to think the lever stays in position because the initial pressure dissolved through the puck and there is no pressure above the piston. I dont think the chamber above the piston is ever under pressure or filled with water.

pab wrote: All the force that you will make afterwards it will be added to that 1bar pressure initially generated by the boiler.

Not for the Microcasa. I just re-examined the group and confirmed the port is below the top gasket when the piston is in the down position. In other words, there's only air above the piston, never steam. The upper port serves the same purpose as the hole on the top of a bicycle pump, it lets air out. Otherwise you'd have to compress the air above the piston on the upstroke. It's my understanding that the Pavoni has the same design, however I have not confirmed.

ogatasan wrote:Dan, from what you say am i right to assume the boiler pressure is effective to the point the port is cut off (Achille aside)... Alchemist came up with that pull pressure mod and provided a curve that led him wonder about a dip shortly into the pull, i wonder there was a possible connection to the piston cutting off the water port.

Yes. To clarify further, the boiler pressure is around 1.0 bar. It's been a long time since my college physics days, but if the boiler is connected to the piston chamber at any point, I would expect the brew pressure to be around... oh, 1.0 bar. Otherwise the brew chamber would be filling the boiler, since there's no check valve.

ogatasan wrote:For me a harder pull (actually push) way over the 9 bar results in a thinner and dissolving crema and a somehow complicated and slightly agressive taste with a tendency towards overextraction.

I think we are seeing the same thing. As stated before I'm learning the motion of a 25~27-second pull. On standard pressure pulls, 25~27-sec extractions give me little thinning at the end. On the other hand, hard pressure pulls begin to thin way earlier than that. If I were to keep on filling the cup (I pull the cup when it begins to thin but finish the extraction just for practice) I would end up with a thinner, over extracted shot with foamy crema. I guess what I'm ending up with is a sort of double ristreto.

What I want to do next is to line up four shot glasses and to break down the shot as it is flowing from the spout. I want to see the flavors at the different stages of both hard pressure and regular pressure pulls.

HB wrote:

pab wrote:The piston lever has always the boiler pressure on its top, when you raise the lever and also during the pull. Hence pressure on the coffee is produced by force on the lever + boiler pressure (example: 8bar from manual force + 1bar from the boiler= 9 bar on coffee puck)

Not true for the lever machines I know.

Oddly, there does seem to be one lever machine that does work like that. The first Faema lever group (the one with the curved sides from the early 1950s) seems to have the volume above the piston full of hot water under pressure. At least that is how the one I am rebuilding seems to work. There is a seal on the piston rod and a rubber gasket between the casting that holds the lever and the cylinder, as well as seals on the piston. Water flows into the volume above the piston and then down around the cylinder liner and under the piston when it is raised.

I'm not sure why they would design it that way, its more complicated than just using the piston to close off the flow, I suspect its something to do with temperature stabilisation. It explains why there is a tap on the top of the group on this model.

On Pavoni millenium above the piston there is always steam under pressure of the boiler and the chamber is sealed from the outside air by this gasket:
http://www.espressoparts.com/prod...Piston_Gasket.html

This steam pressure produce the force that is present on the lever when it's raised because under the piston there is only atmospheric pressure. Instead when the lever is pulled down under the piston there is a closed chamber under pressure that will balance the steam pressure, hence the lever will remain fixed in place (for example at 90° with the two ports cut off).

The Elektra, as you told, does not let the steam enter above the piston.

I am going to jump back to the original question and say I am not sure why there is a perception of less crema with levers. I went so far as to read a similar thread where Jim (Schulman I think) makes a comment that you CAN'T get crema as good on a lever as you can on a pump. This is not quite a gauntlet throw down. I would like some honest feedback. Here are a couple shots from yesterday morning.

As was noted, during the pull I had near 100% crema - no biggie. But these are two full minutes after the pull on my Gaggia Factory. Good color. 50% remaining crema. Tigerstriping during the pour. Virtually no blonding until near 28 seconds. And the most perfect viscous mousetails one could want.

Now, I am not a professional Barista and can't say I have ever seen a 6 out of 6 shot, but I can't find anything wrong with these. Should the crema have stayed at 100% for 2 minutes?





And just to defend the photo the flash REALLY sucks. Way more backflash than I wanted.

OK, where should improvement be?

Very nice crema - you should report the beans, roast degree, age, dose, tamp (approx), and final shot volume. Also the lever pull method. At two minutes that looks like as much volume of crema as a pump machine would still have.

Crema production and dissipation are also influenced to some degree by the cup, just like head on a beer. A tall, narrow cup will hold more crema than will a wider-diameter cup. Also, using a warm, dry cup helps.

Even with the spring lever I often pull 100% crema shots, although I seldom see it last for two minutes like yours (hard to wait isn't it?):

http://www.home-barista.com/forum...r-video-t3687.html

Peace,

PC

Alchemist wrote:I am going to jump back to the original question and say I am not sure why there is a perception of less crema with levers... I went so far as to read a similar thread where Jim (Schulman I think) makes a comment that you CAN'T get crema as good on a lever as you can on a pump.

From earlier in the thread...

HB wrote:That comment is typically applied to spring-powered levers, not manual levers like your [Gaggia Factory]. While I've not measured the brew pressure of my Elektra Microcasa a Leva, Lino calculated its spring is capable of generating about 6 bar at its peak, tailing off to 4 bar. Perhaps needless to say, the crema production of an electric pump machine set to 6 bar is a lot less than one set to 9 bar; the same observation applies to spring-powered versus manual levers. Whether the loss of crema production is offset by a more appealing taste profile is frequently debated.

Try pulling a shot with half your usual lever pressure, let us know what changes.

Alchemist wrote:As was noted, during the pull I had near 100% crema - no biggie. But these are two full minutes after the pull on my Gaggia Factory. Good color. 50% remaining crema. Tigerstriping during the pour...

OK, where should improvement be?

peacecup wrote:Even with the spring lever I often pull 100% crema shots, although I seldom see it last for two minutes like yours (hard to wait isn't it?):

To be honest, I don't know what a "100% crema shot" means. The Guinness like effect viewed through a shotglass while the espresso pours? If so, who cares? I only use porcelein demitasses, which says how little I value it. What does matter, IMHO, is:

• A modest volume of crema and persistence (so it's around long enough to enjoy)
• The crema contributes to the tactile and olfactory experience.

These criteria are about the crema's impact on taste perception, not how the espresso looks during or after the extraction.

peacecup wrote:Very nice crema - you should report the beans, roast degree, age, dose, tamp (approx), and final shot volume. Also the lever pull method. At two minutes that looks like as much volume of crema as a pump machine would still have.

Crema production and dissipation are also influenced to some degree by the cup, just like head on a beer. A tall, narrow cup will hold more crema than will a wider-diameter cup. Also, using a warm, dry cup helps.

Even with the spring lever I often pull 100% crema shots, although I seldom see it last for two minutes like yours (hard to wait isn't it?):

http://www.home-barista.com/forum...r-video-t3687.html

Peace,

PC

Since you asked.

Beans: 1/3 even pre-roast mix of Sidamo, Harrar, Ghimbi, all DP, all from Sweet Marias. My standard espresso blend.

Roast - approximately 14 minute drum roast to FC+ (1st snaps of 2nd), 1st at about 11 minutes.

Dose: grind direct from my Giant Trosser. One leveling tap on counter, with a simple leveling sweep.

Tamp: About 50lbs - until it doesn't move. I go for distribution preservation, not pull adjustments with my tamp.

Pull: 3 20%, 5 lb pre-infusion pulls, very delicate on the up stroke, on 28 sec, approx 9 bar pull.

And, yes, very hard to wait. Which is why it is ONLY 2 minutes.

And HB, I could not agree more with what you say. It is about flavor and crema lends mouthfeel. The 100% is nothing more than the guinness effect you mention. I also don't fret over it. I only pulled in the shot glass for the photo. My everyday shots are in a heavy demitasse skunk cup from Sweet Marias.

The only real weight I put on crema is this. I have NEVER had a great shot that had bad crema, BUT I have had LOTS of crappy shots with magnificent crema. It's an indicator of shot quality, but not shot quality.

OH, lest I not say it - it was a magnificent shot. The third of three actually for the morning. After the 2nd, I decided to take the photo as I was just so dialed in.