Fermenting temps & Fermometer accuracy

The bottom of the modified tube goes about halfway to the bottom of the keg. In case there's any temperature stratification, I would think that position should be a reasonable estimate of the top to bottom average.

 

I don't think you are over thinking this at all . . . proper ferm temp is one of the most important factors in the entire process. My thoughts are ± one degree is pushing it, wouldn't want anything above that. IMO nothing is more accurate than using a thermowell with a temperature probe inside. Here's my setup:



Here's my setup in action. The thermo is a cheap aquarium type (Amazon, about 3 bucks) but is surprisingly accurate. I calibrate with Mr. Thermapen, this one is off by 0.5° (which I add to reading). The thermowell is 15" long and with the temp probe in the very bottom I position it right in the middle of the wort. I add about a tablespoon of water so it's submerged and doesn't swing because of air temp (the water equalizes with wort temp quickly):



I regulate the air of the ferm chamber with a Ranco or Inkbird. Was not pleased with putting the probe of the controller in the thermowell. With a differential of "1" degree I found the fridge would run for hours to drop the liquid one degree. Then it would be off for hours until the entire five gallons warmed up that one degree. As you stated, the heating/cooling will start on the outside and gradually make it to the center. I found it to be more steady (accurate) to leave the controller probe in the air of the fridge and use a fairly high differential, usually 6 or 8 degrees (it's very hot where I live). After a few trails and errors with the diff I can dial in a steady temp with the liquid. My target is for the fridge to cycle about every 45 minutes, similar to your home fridge. Usually it only runs for about ten minutes and the thermo may move 0.1° during this entire cycle.

Of course the act of fermenting changes the temp, but I find that easy to manage. I always start one or two degrees below my desired temp. As fermentation starts, watch the temp rise, then drop my set-point on the controller as the yeast takes off. After high krausen simply reverse the process, i.e. gradually raise the ferm chamber's temp to keep the liquid as desired. This requires me to look and adjust the controller's settings, usually about twice a day. With this minimum effort the liquid is rarely off by more than 0.5°.

A couple of caveats: If you wanted to set and leave town for a long weekend this wouldn't work at all. These aquarium thermometers are cheaply made, they only last a year or two (I normally buy a two pack). Usually the on/off button fails first and you control by removing battery, but I do find they are accurate. It takes some trail and error to manage the air temp in the ferm chamber . . . consider your outside air temp, seals, total volume and probably some more items I don't know. If I was smarter I would place a temp probe in the thermowell and let it drive a Raspberry Pi to cycle the ferm fridge's compressor to maintain ±0.2° liquid temp.

 

“How accurate are the stick-on Fermometer readings?”

One data point I can provide is that I store my buckets with a weak bleach solution. The readings provided by the Fermometer is the same (within 1 degree F) as the ambient I measure with my lab thermometer.

I have no data on comparing the temperature of the Fermometer as the temperature within the middle of the bucket while the beer is fermenting.

I really comes down to what level of precision you think is needed to brew quality homebrewed beer. The Fermometer has ‘worked’ for me over 20+ years of brewing (over 400 batches).

Cheers!

 

Had a contact at a fabrication shop who created it for me. His first question was how many atmospheres of pressure should it be able to withstand! Major concern: I would buy my aquarium thermometer first, obviously diameter of tube must be greater than diameter of probe (~5/16" on mine). You'll see multiple vendors on Amazon with prices all over the board . . . they all seem the same and if it lasts 2 years don't complain. They eat batteries (LR44), usually about the time it approaches high krausen. If you buy spares from Walgreens the battery will cost more than thermo, I get a 10-pack where it's ~50¢ each. Oh yeah, a corny diptube is 1/4" diameter, will not fit. But you see these in homebrew stores for not much more than a diptube.

Be very careful when you drill the lid that you don't oversize the hole. You want the grommet to seal against the thermowell tubing. Your airlock stem is tapered so seals naturally, but Mister TW has straight sides. You want this to be airtight (CO2 tight?). Nothing tricky here, but I would do a "practice" drill before hitting the lid.

I have one old primary with a Fermometer, it usually reads 2-4° higher than the thermowell . . . but it's older than Moses.

That's where the ethanol alcohol helps . . .

 

FWIW:

I use a Ranco temp controller and put the cleaned and sanitized probe directly into my wort.

I do open fermentation x3-4 days, remove probe from beer and clean+sanitize probe, place lid with blowoff on my Spiedel and at this point keep probe in fridge next to fermenter, beer is closed fermentation at this point.

Haven’t had any problems with infection, and tend to think precise temp control for the first x3-4 days is really all that is needed as that is when the majority of all ester/phenol creation occurs.

 

External thermostats don't replace the thermostat of the fridge/freezer, but they override it. You need to set the temp setting of the fridge/freezer at its coldest setting, and then plug the fridge/freezer plug into the plug holes on the backside of the external thermostat's plug (like a piggy-back plug) before inserting that plug into the receptacle. Essentially the external thermostat is controlled by its thermocoupler which you place inside the fridge/freezer (or beer) which then interrupts the power from passing thru its plug into the fridge/freezer's plug, thus shutting off the fridge mechanism, including the interior light. (Which is a bummer when you use the fridge as your beer cellar, thus I keep a flashlight nearby.)

 

Mine is a Johnson Controls analog model that I bought 10-15 years ago. I can't imagine that they have changed much in design (except for going digital), or are much different in the installation from what I described from one mfgr to the next.

 

Some controllers don't have a socket to plug the appliance into. I don't know about the Ranco model(s) the OP is referring to, but controllers that are intended to be mounted on/through a surface (like a keezer collar) do have to be manually wired. It's really not too hard, but I would only use that type of controller for a permanent installation (like a keezer). Or, by lugs he may be referring to internal dip switches used to switch from heating to cooling mode (for example).

 

Well, your beer is still fermenting, so what was your planned fermentation temp? If there was no plan, and assuming your yeast strain and gravity are typical for an American/English stout, you probably can't go wrong with 67-68F.

 

The reason I mentioned gravity was in case this was a RIS or something. For really big stouts, it's a good idea to ferment a little cooler. 66F would be fine though. 67-68F would move things along a tiny bit faster, but you may not even want to, given you'll be gone 9 days.

 

Is there a reason you think you need to do it? Having clarity problems? If I were bottling, I don't think I would cold crash in the absence of a problem. Sucks air (including O2) from the outside of the fermenter to the inside.

(Technically, I cold crash all my beers, because I keg, and if anything comes out of suspension it's going to get sucked up with the first pint or two.)

There's no need to warm up the beer before bottling. But when you use your favorite carbonation calculator, input the end of fermentation temperature, not the cold crashed temperature.