View Full Version : Air temp vs. actual temp of beer in fermenter

01-06-2005, 04:59 PM
I have 14 bbl fermenting vessels and on occassion I only fill them with 7bbl worth of wort. This is traditionally only when I brew big beer i.e. barley wine, scotch ale and the subsequent second runnings. The temperature probes unfortunately are in the straight side of the tank verus the cone so the beer doesn't always reach the probe for an accurate reading. The zwickel is also higher on the tank than the beer level itself. I'm relying on the air temp inside the vessel for temperature control. So is there any formula or good estimation that can be used to get the liquid temperature in a vessel based upon air temperature and empty space? I'd like to have an idea of how low I can drop temperature without freezing?

dick murton
01-07-2005, 08:35 AM
Afraid experience of freezing several hundred hls of beer virtually solid on a couple of occasions says there is no correlation at all. The fermenting wort MUST surround the probe. Unfortunately the rate of heat transfer is so slow as to be ineffective, and gas is a poor conductor of heat compared to water.

Why not try getting a probe on a sterilisable extension and dropping it through th emanway door at the top (or other suitable opening. If you only have to brew like this occasionally then it is not worth moving the fixed probe or installing additional lower probes in each FV, but might be worth buying one as a spare and wiring in each time. Don't forget to check the calibration once wired in.

The only alternative, going back to traditional brewing techniques is to take wort samples regularly (you do do this for the SG anyway don't you ?) and manually control the temperature. With regular sampling control can be reasonable, but obviously not as good as automated systems.

Somebody please tell me I am wrong, and what I should have done differently (apart from take more care to switch to the correct temperature probe !!)


Lager Brewer
01-07-2005, 09:06 AM
Dick, as usual, is right.

There is ZERO correlation between the air temp and the beer temp.

One way to control the temp of the beer is to isolate cooling line on that particular fermenter, and raise the temp of the glycol a few degrees cooler than your setpoint for a few alternating hours of your workday. You will obviously have to spend more time doing this during the primary fermentation. When you are finished doing this, you can lower the glycol temp., shut off the glycol to the particular fementer, and use your normal cooling program for your other beers.

That's what I have done in the past before I could adjust the brew length, and it seemed to work pretty well....and it kept me from freezing the beer if the samples I pulled were in error.

Just a suggestion.

Ted Briggs
01-10-2005, 07:31 AM
My thought would be to make 2 batches and cast them in the same fv. this solves the problem of temp and sampeling and gives you twice as much barleywine!!!
Note to any who would install: always incude at least one fermenter w/ cone cooling and duel probes for 1/2 batches and yeast prop.

01-10-2005, 10:53 AM
I like Ted's solution, and would brew two batches then blend the excess big beer with the small beer I would make from the second runnings. This would be like the old three theds.(porter)
Good luck

01-10-2005, 01:10 PM
Thanks everyone for all your help. However, some of your suggestions are just impossible or atleast very unlikely.
In response to Dick, I can't check gravities when I do this because the zwickle is higher than the level of wort, so now I don't check gravities when I brew this way, I just cross my fingers. I will get a reading when I do finally transfer the beer though and I've always hit my target FG. The idea of dropping a temp probe through the door is a good one and I'm looking into doing that in the future.
Ted, as much as I would love to have 14bbls of barley wine, this is the first batch that this brewery has ever made,considering one 7bbl batch of Scotch ale usually lasts about 10 months the thought of having 14 bbls of barley wine taking up room in the brewery for a year before we even tap it is just not practical...at this point, perhaps in the future if it's received well.

Thanks again

dick murton
01-12-2005, 06:49 AM
If you have a top manway door, then you should be able to drop a sterile sinker jar into the wort, and use this sample to determine you gravity. If you keep all the sampling kit absolutely sterile then you should be able to return the wort back - but don't take any risks. Better some additional losses than infected wort.