I've been using a stick-on liquid crystal thermometer, but I think I'm ready to begin probing the core temperature of my fermenting wort in order to achieve greater control over fermentation.
Here's my concern:
The specific heat of the high density polyethylene bucket fermenter is somewhere between 1.8 - 2.7 J/g.K (joules per grams Kelvin)* whereas the specific heat of the air in my fermenting room at 20 degrees Celsius is 1.005 J/g.K ** If the wort has a gravity of 1.05, its specific heat would be just above 4 J/g.K throughout the possible range of fermentation temperatures for my yeast (Safbrew T-58). ***
What this means is that while using the stick-on thermometer, I'm getting some measurement of the average kinetic energy between the air and bucket (which have greater thermal transfer potentials than wort [ie. lower specific heat]), and the fermenting wort.
Originally Posted by Clementine
If you have spare stainless steel dip tube or small diameter tubing you can make a thermowell (or buy one) then drop your favorite temp probe in there to monitor what is going on. I just made mine x 2 one for a mash thermometer and one for fermenter.
I like Clem's idea because it involves measuring the average kinetic energy between two substances and not three (provided one uses a steel temperature probe). Further, steel has a relatively low specific gravity (.5 J/g.K)**** and thus a better thermal transfer potential than both plastic and air. It should essentially suck the heat right out of the surrounding wort and give one a reading with a much more negligible deviation.
The thermowell has two apparent benefits then:
- Greater accuracy in temperature measurement
- Ability to measure core temperature of wort
I suppose I could drill another hole in my lid, stick a rubber lid grommet into it, then find or make a stainless steel thermowell of the appropriate diameter and length and be all set.
* Material Properties of HDPE, Commodity Polymers | Polymers Data Sheets
***Sugar - Specific Heat Capacity
(SG to brix calculation necessary to use calculator)
****Metals - Specific Heats