santalum Senior Member Joined: 27 Jun 2002 Posts: 215 Location: Australia Expertise: I live coffee
Posted Sun Jan 31, 2010, 10:12pm Subject: Re: Bezzera owners thread - Modifications to my BZ35
I purchased an old and crusty BZ35 on eBay and was pleasantly surprised by the build quality. After rebuilding it worked great but was a challenging for me to get consistent shots. Since it was old and cheap to begin with I didn't hesitate to tinker with the machine with the goal of improving the consistency. The first thing I did was install a dual pressure gauge to monitor the boiler and brew pressures. There were already capped ports on the boiler so this task was easy.
I wanted to improve the group temperature stability so my next task was to install a PID controlled group heater. This mod added about 4 pounds of thermal mass to the group, 600 watts of additional heater power, and made for much faster warm up time. The group temperature is now programmable and stable within one degree. A composite photo of the mod is shown below.
My latest modification was to add pressure regulated preinfusion capability. This involved replacing the rotary pump pressure adjusting screw and spring with a solenoid that is controlled with a timer circuit. I just finished this mod and it seems to really reduce the spurts and channeling that I frequently experienced. A posting with photos and a video is on HB at Click Here (www.home-barista.com)
tedegreene Senior Member Joined: 4 Oct 2005 Posts: 164 Location: JACKSONVILLE
Espresso: Bezzera BZ40 Grinder: Baratza Preciso
Posted Mon Feb 1, 2010, 1:00pm Subject: Re: Bezzera owners thread - Modifications to my BZ35
Manual modulation of grouphead temperatures/grouphead thermometer description and link
Glad to have Farmroast and Ethorson join our discussion.
Ethorson, your mods while very very cool are way beyond my abilities. Just yesterday I figured out how to adjust the grouphead temp using a manual method however and it has had an immediate positive impact on my pulls. See earlier discussions regarding flush timing if you are interested in background. Basically I had trouble getting my pulls above 197 regardless of my flushing routine, I could get cooler pulls with the longer flushes described by owners of other designs but even omitting a flush wouldn't get me higher.
I installed a semi permanent grouphead thermometer a few days ago by running the thermocouple wires under the portafilter gasket and securing the tip to the screw that attaches the shower screen. I found that in general the temp during the pull would remain about where the grouphead temp was at the start of the pull regardless of my flushing technique. If I tried a long flush to warm up the grouphead the water flowed too fast and the grouphead wouldn't heat up much before the HX water got too cool to do the job. It seemed most of the heat was being lost with the steam billowing out. Then the Head would cool back down during the time needed to reheat the now cool HX water and I'd be right back where I started. As an experiment I bumped the brew button to allow just a squirt to fill the empty portafilter stopping as soon as the first bit of steam escaped from the spout. The temp fell from 200 to 198, I assume from cold water in the pipe between the HX and the grouphead. I paused 2 or 3 seconds bumped again and got the temp 202. The next pause/bump/pause raised the grouphead/portafilter temp to 205, another got me to 207 then 209 and I decided to try a pull from there. The temp fell to 206 while I was grinding and tamping a test dose but without additional flushing remained there throughout the shot pull. Wow what a hot cup I had, not a God shot to be sure but not all that bad either. Not burned but perhaps a little bitter.
That description sounds real tedious but in practice this morning it wasn't bad and added almost nothing to the total prep time. I just bumped between the steps of my normal routine. It went like this: Bump the button until steam just starts hissing from the portafilter spout then measure beans into the grinder's hopper, bump then pour milk into the pitcher, bump then grind beans into a glass, bump remove the portafilter-dry-fill with coffee and tamp. Now the temp gauge is at 206, flush and the reading starts falling after the water dance slows; 205,204,203. Stop, lock the filter and pull with no delay for a 202 degree shot. Shorten the final water dance flush for higher pull temps or extend it for lower.
This is of course, very preliminary. I think the process I've described is probably more elaborate than it needs to be since I achieve a higher than necessary starting point but this was the first day and more practice will be needed to perfect and simplify the procedure. It looks like I will be able to quickly hit any specific temperature I desire from 209 on down and with precision after I work out the details.
Hey Retfeg, I did manage dream cups 5, 6 and 7 this morning after months of taking wrong paths. So donít give up. The journey's been fun if sometimes frustrating. It's all about trying different approaches. The higher temps moved me from a good cup to great or nearly great one. Only thing is, now the barís been set a little higher for my next dream cup. That's how it's gone with my learning curve. I reach a plateau where I my single parameter at a time adjustments from where I am donít seem to improve things. Trying one thing at a time takes so long I feel like giving up then one day I hit on the one thing that does make a positive impact, sometimes by accident and I start all over looking for a new way to raise the bar again. Meanwhile Iím enjoying coffee better than I can get anywhere locally. It's not the fish you caught nor the golf shot you made that keeps you coming back to those hobbies. It's the one that got away that turns a hobby into pursuit and it's all about the chase. I'm OK with that too.
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