[Homeroast] Sunbeam Vac pot tuning: a simple solution
Ryan M. Ward
silvercro_magnon at hotmail.com
Thu Apr 15 03:55:52 CDT 2010
"Ice can exist at 30°F, 20°F, -20°F, -40° with little effect on the ice bath
temperature. Ice absorbs most heat when it melts. (32° ice --> 32° water).
It's a stable temperature regulator only at 32° F. There is no regulation at
any other temperature,"RayO brings up a very good point here that I didn't even think to mention. It is a weird fact of nature(well, not that weird, there are stranger facts of nature), that although water can take on any temperature between melting point and boiling point- and ice can take on any temperature between absolute zero and 0 Celsius, ice water, once it has reached a uniform temperature- is always 0 degrees Celsius(32 F, sorry- I exclusively use Celsius and Kelvin temperature scales in life, I honestly never use Fahrenheit and don't know Fahrenheit temperatures very well, the one exception to this rule being that I steam my milk to 150 F, when I worked as a Barista, I was trained using Fahrenheit).
This is why thermometers and thermocouple readers are calibrated with ice water that has been allowed to sit for 10 minutes- its pretty reliable.
In fact, all the way up until the 50's the Celsius temperature scale used to be defined in terms of the melting and boiling points of water(0 is melting, 100 is boiling) at standard atmospheric pressure.
Ryan M. Ward
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> Date: Thu, 15 Apr 2010 00:22:49 -0600
> From: raymanowen at gmail.com
> To: homeroast at lists.sweetmariascoffee.com
> Subject: Re: [Homeroast] Sunbeam Vac pot tuning: a simple solution
> You say " The result is water at 200-203 F each time in the upper globe and
> very nice coffee."
> I am sorely tempted to ignore the political scene, international terrorism
> and posit that the temperature was not the "200-203 F" you imagine. That's
> 1.5% precision- Not with a meat thermometer that can't be calibrated or read
> that closely and improperly installed. A frangible device, poorly installed
> with toxic contents sounds like a sequel to Poe's *The Pit and the Pendulum*
> Without instigating quarrels, flaming, etc,- if the result already is "very
> nice coffee," what more do you want? For a certainty, if you keep tinkering
> your results will change. Some better, some worse. Keep notes. Small
> increments in grind size, along with time and the mythical temperature
> control make the brew.
> Ice can exist at 30°F, 20°F, -20°F, -40° with little effect on the ice bath
> temperature. Ice absorbs most heat when it melts. (32° ice --> 32° water).
> It's a stable temperature regulator only at 32° F. There is no regulation at
> any other temperature,
> You would never use a precise Hg thermometer around food stuff, but note
> that for basic research use, the proper calibration check procedure is to
> fully immerse the thermometer body in the heated medium (water or oil) and
> compare the 10% FS and 90%FS readings for Ø and Full Scale, against a
> mercury standard thermometer. Most physical devices are non-linear and
> useless at the extreme ends of their scales
> Unless your thermometer is thus calibration-checked along with that of a
> separate technician, the two can never duplicate each other's results, Most
> people using cheap (<$100) thermometers or a bad installation, couldn't tell
> the difference between 200°F and 203°F, if their life depended upon it. If
> the coffee already rates as "very nice," and you can repeat it stop talking
> and start enjoying.
> If you don't know anything about parallax scale errors, a digital
> thermocouple readout probably won't help, given a poor initial installation.
> How many grad students wanted us to instrument their projects with new
> thermocouples, connectors and lead wire "for accuracy," for free. Beggy
> Cheers, Mabuhay -RayO, aka Opa!
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