Fermentation Temperature Control Question

Hi,
I know that temperature control will go a long way to brewing better beer. My question is there an online calculator or something like that, that can predict how long it will take to get your beer/wort to a certain temp. Something like my beer is at 68 degrees and put it in a 42 degree kegerator, how long will it take to chill the five gallons of beer down to 42 degrees. I know this may be impossible since there are too many variables i.e. shape and size of container, whether the vessel is plastic, glass, or metal among other things. But if you dont ask.....

I'm not aware of a calculator that does what you're describing. Like you said, it would likely have too many variables to make it very exact anyway.

If you're going to use a refrigerator, the best way to control it's temperature is an external temperature control unit. It will shut off the refrigerator's compressor when the probe tells the unit that the correct temperature has been reached.

Ranco Digital Temperature Controller (Not Wired) | MoreBeer

I tape the probe directly to the outside of my bucket. That reading should be within a degree or two of the temperature you want. It's a fairly precise way to control the fermentation temperature.