heavyduty wrote:Dan, I was just wondering if the OPV on the Silvia you are using has been adjusted or is it factory set?
I checked brew pressure when it arrived with a Scace II thermofilter and it was 9 bar at double espresso flow rates, so I didn't bother with over-pressure valve adjustments. If you pull lots of ristrettos (and thus the OPV is necessary to reduce the maximum pressure), it's worth adjusting the OPV. I still don't get it: Why adjust the OPV?
explains this point at length.
heavyduty wrote:Also, I've never played around with preinfusion on mine. Do you have an opinion on the best way to do this (maybe even a video) and if it truly helps?
If you want to experiment with it, see Don's Rancilio Silvia Preinfusion Technique
, summarized below:
vanboom wrote:1. grind, tamp, etc.
2. place a pitcher under the steam wand
3. set the steam valve slightly snug (allowing some water to flow at a very slow rate out of the steam wand)
4. lock in portafilter
5. press the brew switch: listen to the sound the water is making through the machine
6. tighten the steam valve a second or two after you hear the puck fill (yes, you can HEAR it)
7. finish extraction
If you listen carefully to the second pull of the "blooper" video above, you'll hear the pump tone change because I was following the above procedure. I also tried "prewetting" the puck by flicking on the pump for 2 seconds, waiting 2 seconds, then starting the pump again for the extraction. Both techniques do increase the margin of error a tiny bit. Personally I prefer using a deeper basket instead like the EspressoParts 14 gram
or 21 gram
. The extra headroom allows an extra second or two for prewetting the puck.
MountRoyal wrote:Do you believe that the screw was the main cause of the channeling?
The screw didn't cause the channeling, it indicated the puck clearance was insufficient. The Rancilio Silvia, in my experience, demands extra headspace to allow the water to more evenly diffuse over the surface of the puck prior to full pressurization. I would only replace the stock screw if I wanted prettier looking pucks post-extraction.
MountRoyal wrote:It would be interesting to see your tests with a PID...
Long answer: Rancilio Silvia Flash Review - PID temperature controller
. Short answer: Adding a PID eliminates the need to temperature surf and thus increases convenience and potentially consistency, but for a patient, skilled barista, it doesn't change Silvia's espresso potential.
MountRoyal wrote:Would a lower pressure diminish the channeling?
Yes, lower brew pressure increases your margin of error. I recommend adjusting it to around 9 bar. But don't take my word for it, try it yourself. To really get an idea of what's affected, bracket the results with a good delta between each set. For example, try the brew pressure at 7 bar, 9 bar, and 11 bar for a few days each and then narrow in on the one you prefer. Typically the lower pressure settings will channel less, but crema production will suffer and the taste may go flat. At higher pressures, crema production peaks, but the risk of channeling increases and the taste may go bitter/acrid.