Ferm temp, ambient vs wort

[Toy4Rick]

So while setting up a very rudimentary temp controller in my fridge it occurred to me that I don't know what temp we should monitoring, the ambient temp/the temp of clear water in the fridge or the temp of the wort as it ferments

The reason I ask, I placed a gal jug in the fridge with a thermometer, it read 62* while the fermometer was reading 68*. I have never used a temp controller and only relied on the fermometer in my previous brews

This might be a simple thing and I am just over thinking it

Rick

 

[Beernik]

Fermenter temp (wort temp) is what you want to monitor and control.

 

[BroStefan]

What you care about is the temp of the beer, not the air around the beer.

Tape the probe to the outside of your fermenter - blue painters tape works well for this - and cover it with something to insulate the probe from the ambient air. Fold up dish cloth or a couple of layers of bubble wrap work well. It at take a whole but the beer will settle at the set temp and the ambient air will settle down, too. 5 gal of suggest water has a huge thermal mass compared to the air.

 

[WoodlandBrew]

The difference in temperature that you are seeing could be due to the accuracy of the measurement devices. You might want to calibrate your thermometer using ice water.

details:
http://woodlandbrew.blogspot.com/2013/01/how-to-measure-thermometer-drift-to.html

 

[Wynne-R]

Careful. There’s a big difference between ice water and a proper ice bath. I got this from a chemist buddy:

If you can be assured of linearity the water melting point, boiling point calibration is pretty damned accurate. The tricks are:

The water/ice must be pure, as in distilled. Use slush (crushed ice) with the water level slightly below the ice. When determining melting point remember that water is densest at 4C so the ice/water mixture must be continuously well stirred or the water at the bottom will be 4C and the rest of it somewhere between 0C and 4C (magnetic stirrer works best). A steady well-stirred temperature is 0.0C.

Got it? More ice than water and stir it.