Posted Sat Jan 30, 2010, 4:39am Subject: Re: Bezzera owners thread..Why do you hate/like/love your machine? Tips and Tric
Hello to all my Bezzera peeps,
I really like my machine, but I do have a few negatives about it that I'm trying to work out.
First of all, GATORRPH - My understanding of the heat exchanger is a little different. It seems to me to not be much different from a normal heat exchanger, although I could spend more time looking at other heat exchangers to see different designs. I'm not sure that what you describe as the water mixing is exactly what's happening. The HX is more of a chamber than a pipe as you've mentioned, so I suppose it doesn't flow exactly las the diagrams depict, but the general flow and heating process seems like a normal heat exchanger to me. What might be unique is that the inlet is a tube that carries cold water to the back of the heat exchanger, then it travels back , but outside of that pipe, like a heat exchanger within a heat exchanger.
Anyway, what I'm finding to contribute to the unique flushing requirements for Bezzera (at least my particular machine) is an extremely high water debit. I started a thread recently about this: "flow rate: is there something wrong here?" The replies I got started me on the crazy journey of learning all sorts of new lingo and I'm still in the middle of it, but basically I've decided to turn my attention to the water debit (flow rate of water without the portafilter).
Here are the symptoms I've had lately, which has caused painful amounts of wasted delicious coffee beans: -Many sour shots (low water temp) -The area between tight ristretto and dishwater spritzer (bottomless PF) was very narrow. -early blonding I should mention that I have in fact experimented with flushing a lot, it just wasn't working for me.
It seems to make a lot of sense to me, but I haven't found a lot of information about water debit for HX machines. Given a very high water debit, the temp in the HX will drop rapidly. I've found the rebound time to be necessary, but this seems to explain with so many BZ users are using a short flush. It seemed to me that a slower flow would have a slower drop in temperature which appeals to me for brew control. If an HX is designed to have a steady temperature during extraction flow rates, then it seems a free flow rate should only be a little higher, to allow a steady decline to the desired temperature. Additionally (and this may all be in my head, I haven't read it anywhere but it makes sense to me) there is an aspect of heat shedding in the tubing between the HX exit and the brew screen, and during the rebound time, this area is likely to become a bit under temperature.
The other aspect of water debit that is talked about more (including double boilers) is the benefit of pre-infusion. It's not a timed/pressurized pre-infusion like some machines have, but with the water flowing at a slower rate, there is more time for the water to hit the coffee before the pressure and resistance build up. The other thing is when the the water is introduced at such a high flow rate, it will disturb the puck and have a higher chance of channeling. The consensus I found after reading various discussions was that 60-90 ml in 10 sec is a good flow rate, and a lower flow rate will be more forgiving for extraction. My machine runs at about 200 ml in 10 sec.
So I looked into figuring out how to slow down my flow rate. there is a piece called a gicleur (gigler, giggler, bezzera calls it a jet) which is located at the exit of the HX. I took it out and the hole diameter which controls the flowrate was on the larger side (appx 1 mm). In the discussions I came across (non-bezzera) people found .5-.7 mm to be good. I'm in the middle of making a new jet/gicleur (waiting for some tiny drill bits to come in the mail) but I had a temporary fix, to just try it out and see what happened. I put a small section of a paperclip in the hole, bent it so it was locked in place and put the piece back in (yeah, a little ghetto). Basically, the paperclip reduced the flow by decreasing area of the hole. After a few tries, I got a flow of about 75 ml in 10 sec, right on the money. Suddenly I had more control over my shots. My shots were no longer sour and I finally saw the red tint on my crema. Also, the spritzer dishwater shots were much more under control and I could finally make a standard double ó no early blonding.
That solution was temporary and I'm still in the middle of fixing it and I think I'll aim for a slightly higher flow rate than my test, but I think it's really going to help.
Sorry to be so long-winded. It seems like the high flow rate and quick flush is working for a lot of people. I think it's one of the things that really makes a machine require different technique, but personally it just wasn't working for me. I'm really getting excited about this modification. The one thing I'm worried about is that since the pressure gauge is located before the gicleur/jet, there will be a reduction in pressure, so I'll be a little lost. If I only had a scace device!... but that's way out of my league.
On another note (maybe it's related?) my machine is really loud! Hopefully there's not something wrong with the pump. Good to hear that others have quiet machines though. When I got the machine (used) I was really excited to read that rotary pumps are quieter than vibe pumps, but boy was I surprised! Maybe I can figure out how to make it quiet down.
I switched to a 2-hole steam tip which worked really well. I got it from chris coffee. I still need to find a gasket that fits the new tip though. There's a small gap which can collect milk.
OH! one more thing. This will probably change when I finish my mod, but I've had a lot of problems with coffee not extracting from the middle. I've had to counter this with a concave distribution, using my grinder lid to make a clean dip in the middle before tamping which generally worked. Anyone else have this problem? I'm also considering a convex tamper at some point.
tedegreene Senior Member Joined: 4 Oct 2005 Posts: 164 Location: JACKSONVILLE
Espresso: Bezzera BZ40 Grinder: Baratza Preciso
Posted Sat Jan 30, 2010, 8:57am Subject: Welcome to the thread Cracklebox
Cracklebox, Thanks for contributing to the thread. I too worried about the high debit, perhaps based on your flow rate post. Mine is about 220ml per 10 sec. Funny, I tried the exact fix you describe except using a small gauge copper wire instead of a paper clip. It reduced the flow by half but didnít seem to have any impact on the quality of the cup and it started giving me frequent clogs so I removed it (I had recently de-scaled). Iím not convinced a slower debit would have much effect on the cup and wonder if the difference you describe is due to a change in the temperature profile with a slower flow into the HX causing less turbulence/mixing. The flow is 2ml per sec during the pull (assuming two 0z per 30 sec) so Iím not sure what significance the unimpeded flow rate has. Some have stated it could be too low but high wasnít a problem. To address the issue of initial flow rate during the pull and pre-infusion, I have considered and will probably explore at some point, switching the pump on after a delay when starting the pull. Pushing the green button should allow water to flow though the open solenoid with just line pressure until the pump is engaged if a second switch is installed.
Perhaps a rebound is called for after flushing (or splashing) if the bean you use likes elevated temperatures. I just hit the button momentarily for a splash before I pulled this morningís cups and still got only a 198 degree pull. I have my p-stat set to cycle from 1.2 to 1.45 by the way, so should be starting with a high average temp. I'm not sure how the machine pulls the temp down so quickly with a small squirt for a flush but my bean does fine at the temps I'm seeing and it's just impossible to burn the coffee. The temp is absolutely stable throughout the pull. I certainly donít know for sure whatís happening in the HX chamber, my description is merely a theory based on observed results. Photos taken during rebuilds and posted on the forum by others indicate at least some HX designs have just a straight copper tube running through the boiler with a one way flow from one end to the other rather than a chamber . I donít think much cold/hot mixing could occur in those machines as there would be close to zero turbulence with a continuous column of water running through a uniform diameter pipe. The cold would simply push the hot ahead of it and super hot water would flow until it was completely exhausted from the tube. Then, during the extended rebound, the water in the HX would heat but the water in the tubes between the HX and the group head would cool and you would hit the coffee with cold water at the start of the pull, maybe thatís a good thing but I doubt it. I will experiment more and report my findings now that I have the temp gauge hooked up again .
The screws holding the SS front panel to the frame on mine were loose and the panel was vibrating making a pretty loud rattle. The screws looked awkward to get to and I happened to be in the process of leveling the slate on my pool table so I just shoved a wood shim I had handy between the panel and the frame from inside the cabinet so it doesnít show, thinking it would hold me over short term. That was a couple of months ago & the machine is quiet enough that I forgot all about the problem. The shim might work better than a screw down as it provides a rattle proof sound cushion between the metal pieces. Push on the front panel behind your group head and see if it makes a difference in the sound level also look for other rattle problems. The pump itself isnít really all that loud.
Posted Sat Jan 30, 2010, 1:47pm Subject: Re: Bezzera owners thread..Why do you hate/like/love your machine? Tips and Tric
I still have a lot of experimenting to do! Unfortunately, I can't really test the different gicleurs side by side since the machine needs to cool. Also, I'll have to save the serious research for later (2 weeks), when I can play with my toys and not feel guilty that I'm not busy studying. Jammin, thanks for contributing your measurement. It looks like it's the semi-commercial machines (heavy duty pump) that have the higher debit. I'm not sure why that would be preferred in a commercial setting, but it seems to bring out a difference in technique with the BZ-40 and 35 accommodating a less fussy italian style prep. Like I said though, it just hasn't been working for me. GATORRPH, I'm finally understanding what you mean about the effect of turbulence and mixing the water. I wonder if there are any espresso machine technicians that can chime in on the different HX designs, primarily tube vs chamber. It seems that there must still be an effect of continuous/linear flow as well. I'll try some even shorter flushes and see what happens. As I mentioned though, I'm also having extraction problems aside from temperature. During your flush, does the water spray out toward you at all? When I'm flushing superheated water, I always get sprayed a bit and my prep space in front of the machine always gets wet. I also attributed this to the high flow combined with the the exploding hot water. Also, good to know there are some possibilities to calm the rattling. When i had the top off and the machine was on but cold, I noticed that I could pinch some pipes and it would quiet down, so after I try your shim idea, maybe I can brace the pipes a little more too. So much work/play to do with my machine. I can't wait until I have more time.
Anyway, it's great to see Bezzera users come together. Since the topic of steam tips has come up, has anyone tried to install a new steam wand? I've been lusting after the no-burn steam wand and I'm wondering if it's possible to install.
GATORRPH, Since we have the same model, do you leave your machine on all the time or turn it off and on every day? I don't use mine every day and I have roommates that might be annoyed by me leaving the machine running all the time (electricity bill), but I'd like to have it on all the time, then I'd use it every day. I wonder if keeping the temp up and stable will actually not cost so much more. I guess this is a non Bezzera specific topic for another thread. I'll do some searching.
Let's keep this thread alive, I'll post some pics when I have some more time to play. In the mean time, I'll mostly be using my french press. -daniel
Posted Sat Jan 30, 2010, 2:01pm Subject: Tips and Tricks
BZ07 4-hole steaming tip
I did the tooth-pick trick to plug one hole. Made a serious improvement to my frothing in my 8oz pitcher. I think it will still allow me to have ample steaming power for larger pitchers as well. Thanks the for the idea GATOR.
PS: mods - can you please shorten the title, it is causing problems for us when replying - error in the title becomming too long. thx
Hi Jackson, This comes up occasionally, and it is a pet peeve of mine as well.
But the mods are actually supposed to avoid making edits for content, and that includes titles. The Coffeegeek moderation policy is that this is a "free speech" domain and the only time moderation is used is when rules are broken...and then it's generally preferred to delete rather than edit for content.
Also, each post has it's own title so we would have to edit them all....which I would absolutely be willing to take care of for y'all but I should have explicit permission from all of the thread contributors first.
I like the way you shortened your post title to "Tips and Tricks", and another possibility would be to remove the "Tips and Tricks" from the other post titles to read: "Bezzera owners thread..Why do you hate/like/love your machine?"
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