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Topic: Silvia question (3 msgs / 167 lines)
1) From: Mike McGinness
From: "Kathy Hawken" 
Always enjoy reading your posts online.  Do you have a Silvia and if so,
what's your experience been?  Older model with 100 t-stat or newer...PIDed?
I've new model with 100 t-stat, changing over to 110 t-stat in a few
days......have issues with temp instability (so I can assume at this point)
and leaning towards PIDing her or upgrading to a HX and E-61....$$$$ model.
Thanks in advance for any input you might conjure up.
- Kathy
Hi Kathy, (Greens spreadsheet to follow in separate email shortly.)
cc'd list since others may find beneficial (or have corrections!)
Yes Miss Silvia lives here. She moved in Feb' 02. Don't know which which
t-stat and not PIDed. I temp' surf each and every pull. Simple actually.
First she needs to warmup a good half hour of course (or 'cheat' for ok shot
in 5min.) I pull just water through the PF until the heater light comes on,
remove PF & rinse (with hot water on demand:-) - dry - load grinds - very
lightly tap - level grinds with finger or Rocky doser lid - med firm tamp -
ligthly tap - firm tamp and polish. Heater light goes out about now. Lock
and pull 'bout 15sec after heater light goes out. After shot I remove PF -
flush head 'till heater light comes back on (into ss measure cup - came with
Rosto!) - dump puck (into garbage disposal) - rinse PF (hot water on demand
again) and either replace PF in head or re-load! If doing back to back shots
timing works out just perfect for heater light to go out for next shot... I
don't plan on adding PID, don't see the need. The 'surf' may seem a pain
before each shot or series of shots but it's just part of the 'usual ritual'
for me. Back to back shots it doesn't add any time...
MM;-) aka Kona Krazy miKe mcKoffee
Variable Variac Rockin' Rosto Roasting
Rocky grindin' - Miss Silvia brewin'
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2) From: Greg Scace
Hi Kathy:
  In reply to your email to the home roast list:
Do you have a Silvia and if so,
what's your experience been? Older model with 100 t-stat or newer...PIDed?
I've new model with 100 t-stat, changing over to 110 t-stat in a few
days......have issues with temp instability (so I can assume at this point)
and leaning towards PIDing her or upgrading to a HX and E-61....$$$$ model.
Yeah, I got one.   It rocks!!  It still has the 110C thermostat, but it is 
also PIDed and has brew pressure control.  I call it Bride of 
Frankensilvia.  I've used it to do some research into the effect of various 
parameters on espresso quality, and to also make some ass kicking 
espresso.  My opinion on Silvia is that she has very good thermal stability 
when one is brewing, but the shot to shot repeatability of the stock 
machine is not so good.  This isn't really a problem because you can learn 
to temperature surf.  It would suck if the brew water temperature varied 
during the 25 second brew time, but the design of the boiler is quite 
clever and keeps water temperature constant over the short term.  All non- 
HE single boiler machines use inexpensive snap action thermoswitches to 
control the temperature.  These are bi-metal switches that turn on when the 
temperature drops to some threshold level and turn off when the temperature 
rises to some threshold level.  I think the spread between low an high temp 
is something like 10 C (18F).  That makes it pretty hit or miss for getting 
the right brew temperature, but you can improve that dramatically so that 
you are always brewing at the same temperature if you follow the 
temperature surf instructions on Randy Glass's website at http://www.quiknet.com/~frcn/Coffee/Coffee.htmlI noticed that Mike McGuiness told you how long to wait for the surf time, 
but an important concept was lost in what he told you.  The surf time that 
you wait is specific to your machine, your taste buds, and the blend that 
you are using.  You can easily find the time that works for you by 
increasing the surf time by 15 or 20 second intervals until the espresso 
becomes bitter.  Then shorten the surf time by 10 second intervals until 
the taste sweetens up again.  The difference should be pretty dramatic if 
your beans are fresh and you are using a blend such as Sweet Maria's Monkey 
Blend or Barry Jarrett's Decatur Street Blend (Riley's Coffee and 
Fudge).  Once you've found the surf time that works for you, you're pretty 
much set unless you change blends, or thermostats.
Temperature surfing should really help you out in improving 
repeatability.  If you are so inclined and not afraid of getting into the 
guts of your machine,  I would definitely recommend PID control.  PID gives 
better than one degree shot to shot repeatability, allows extremely easy 
temperature changes to accommodate different blends, and benefits steaming 
as well since the temperature readout from the PID controller lets you heat 
the boiler in steam mode until just before the steam thermostat clicks 
off.  If you start steaming at the highest possible temperature you will 
get highest steam pressure.  If the heater is still operating when you 
begin steaming, the pressure will remain high and steaming will really 
improve.
I am of the opinion that most HE machines cannot hold a candle to a PIDed 
Silvia in terms of thermal repeatability.  This is because pressurestats 
can't do as good a job of temperature control as a PID system and because 
the heat exchangers must be used under conditions of constant throughput if 
you expect consistent temperature at the portafilter.  HE machines do offer 
simultaneous steaming and brewing capability, but this is not a big benefit 
If you are not making lots of milk drinks at a time.
I have recently done some experimentation wrt brew pressure control.  I am 
interested in why people think rotary pumps are superior to vibe pumps, and 
what the effect of pressure is on the brewing process.  I can say with 
certainty that the Silvia brew pressure is too high, as is the brew 
pressure of most vibe pump machines.  My measured brew pressure for 
non-regulated Silvia was about 185 psi, which is around 12 bars.  9 bars is 
considered optimum.  I installed a pressure gauge and adjustable pressure 
regulation system in my Silvia so that I could quantify the effects of brew 
pressure on the quality of the coffee coming out of my kitchen.  I believe 
that pressure regulation is a big step forward and I suspect that the main 
reason that people think rotary pumps are superior doesn't have anything to 
do with the pump type per se, but has more to do with the lack of pressure 
control on many vibe pump systems (such as Silvia's).  I am going to do 
some blind tests in late February using a Wega Mini-Nova HE machine with 
rotary pump, my Silvia, and various combinations of pressure control / 
non-control and publish the results on alt.coffee.  There are a couple 
local alties that are interested in doing this work and have agreed to be 
guinea pig taste testers.  I am quite hopeful that we will learn something 
about the effect of various pumping schemes on espresso quality. The 
results of this will also have some immediate benefit for Silvia 
owners.  The Silvia employs a pressure relief valve that is used to protect 
the boiler from over-pressure due to thermal expansion of liquid water 
during warmup.  It's very easy to modify this valve to open at a lower 
pressure, and become a pressure control valve.  I intend to publish the 
how-to on alt.coffee in late Feb. as well.
It should be pretty clear that I'm a big fan of Silvia.  I really like the 
idea of dedicated brew boilers over he machines in terms of thermal 
stability, provided that good thermal controls exist as part of the machine 
(PID being a good example).  Short term stability of Silvia has been pretty 
well documented.  Temperature surfing techniques are easy to learn and can 
make the stock machine really perform well.  And Silvia is easily modified 
to perform even better!
-Greg
By the way, in case you're interested in why I'm not going to do any of 
these studies until late Feb., check out www.sailfaster.org
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3) From: EuropaChris
Hi, Greg.  I am VERY interested on this mod for the pressure relief on the Silvia.  I, too, believe the main reason for the alleged superiority of rotary machines is the pressure regulation, and why ristrettos particularly are much better on a rotary machine.
Think of this - Ms. Silvia will develop at least 12 bar. Using 'w' pressure to get 'x' amount of espresso in 'y' seconds, you need 'z' grind fineness.  Vary any parameter, and the whole system changes.  Compared to a rotary 9 bar machine, I will have to grind much finer to get the same amount of espresso in a given time period.  A finer grind over the same 25 to 30 second extraction will produce a different cup, even though ending up with the same amount of espresso compared to that rotary machine.
Now, this doesn't take into account the pressure curve of the Silvia pump.  Deadhead, 12 bar is it.  But, what's the max pressure at brewing flow rate?  Still 12 bar??  Probably close to it, eh?  A rotary machine makes it's 9 bar and that's it.  You can therefore vary flow easily by grind fineness.  On Silvia, the finer you grind, the more pressure the pump will develop up to it's maximum capability.
This is also why I seem to prefer a 2-1/2 oz. double from Silvia.  I'd wager that this flow rate over 25 seconds roughly equates to 9 bar.  If I grind finer to get a proper ristretto, I get a harsh cup due to the very fine grind overextracting.
Chris
Greg Scace  wrote:
  The Silvia employs a pressure relief valve that is used to protect 
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