Temperature Issues Beyond Reason

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Early this morning I brewed a Chocolate Oatmeal Stout. This is the first 12-gallon batch on "my" system. I possess a 14.5 gallon conical fermenter, so why not fill it? Since it was my first big batch, it was not without problems and a lot of learning. I learned a valuable lesson about combing 24.75 lbs of grain along with 8 gallons of water into a 10 gallon mash tun. It worked, but just barely. Surprisingly, I achieved 86% efficiency, as compared to my usual 74%. This is fantastic, except the beer is now not within style. Oh well. I also learned that multi-batch sparging (more than my usual 5 gallon 1 batch sparge - due to the mash tun volume), when you only have one burner, means having to lift a very heavy brew kettle onto the burner. Something I thought I was finished with after I began using a pump about 6 months ago. Lastly, I discovered something I have been a victim of before, and I thought I had learned my lesson: temperature control.

3 years ago, when I really got into brewing beer, I used two separate digital thermometers. One was a Taylor brand from Walmart, and the other an Oneida brand. I had problems early on with my beer coming out very thin and without body. It turns out the Taylor was completely off at almost any temperature, while the Oneida was off at higher temperatures and the probe had gotten wet. The probes are not designed to have the cable submerged, because the cable/probe junction is not watertight. I had been scratching my head trying to figure out the what/why/how until I purchased the Cole-Parmer Workhorse Thermocouple.

I don't believe they make this model any longer, but it was about $50.00 and it is a type-K thermocouple, meaning one may purchase any generic type-K temperature probe and it works like a champ. Not to mention it comes with a certification that says it is accurate. Walmart specials do not come with any such certification.
A side-by-side comparison in both boiling water and freezing ice water told me what was going on with my digital meat thermometers. I threw the Taylor in the trash, and used waterproof tape to seal up the probe on my Oneida, since it was consistent with the Cole-Parmer.
My beer was instantly better.
Fast-forward a couple of years to May of 2012. I purchased my stainless conical fermenter from conical-fermenter.com. The owner is based out of Portland, Oregon. I happened to have a class I was attending in Portland and it all worked out. The conical happens to come with a thermowell and an analog dial type thermometer. I have fermented ten or more batches of beer in that fermenter, and one of my last batches, a Bohemian Pilsner, has diacetyl . I raised the temperature on my fermentation chamber to perform a diacetyl rest, where the yeast are actually supposed to consume the diacetyl. I also had another relatively serious fermentation problem with a Baltic Porter back in October. Those two batches in particular don't really make sense because I did everything I know to do. I can control my fermentation temperatures to plus or minus one degree using a dual stage temperature controller from Control Products. My temperature probe is placed in the top of the unit. I figured there was enough air circulation with the fermentation chamber's internal fan that temperatures would be relatively consistent throughout.
It had never occurred to me to calibrate my fermenter's thermometer. There is a screw on the back for that purpose. Today I used my trustee Cole-Parmer and it said my wort was 64*F. My fermenter's thermometer said my wort was 69*F, a five degree difference. I also have an analog refrigerator thermometer set on top of the fermenter and it read 64*F. I believe, all this time, I have been five degrees low on everything I have been making. For some things it may not have played too much of a role, but certainly, it is the reason I have diacetyl in my Pilsner (it's okay if drunk really cold - just like Coors Light), and also is more than likely the contributor to the stuck fermentation of the Baltic Porter.

I had been down this path once before and I have no idea why it never occurred to me to calibrate my thermometer. I calibrate my refractometer every time I use it, so why not my thermometers? I encourage everyone to check out their thermometers. Calibrate, purchase, throw out, etc. all of your brewing temperature gear/devices. It just isn't worth screwing up another batch of beer. I now have high hopes for my Chocolate Oatmeal Stout.
I believe this type of problem is rampant in the home brew arena. I myself have had this problem. Please Calibrate all thermometers. Measure with two different ones when possible and from 2 different locations on the same tank when possible. You will be surprised.
I only brew small 5 gallon batches, but I am obsessed with temperature control (A byproduct of my profession in the HVAC field). I have lots of temp probes, and so far I have loved this one by UEI (even though I wasn't a fan of their Phoenix clamp multimeter, which I replaced shortly). http://www.amazon.com/UEi-DT302-Digital-Logging-Thermometer/dp/B003RY8VZ2/ref=sr_1_15?ie=UTF8&qid=1365822733&sr=8-15&keywords=uei+temperature+probe
I use this at work constantly to measure outputs on supply ducts, and delta t's on refer and ac equipment. It also has the unique function of being able to be strapped to a pipe, duct, or carboy and measure the precise temperature range over a few days, which you can plot on a graph with the provided software. Great for finding the best spot in the house to let the bucket sit during daytime setbacks and whatnot.
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That unit looks great, especialy the ability to take input from 4 different types of probes. My Cole-Parmer is Type-K only.
I totally agree! Thermometers exist to screw up our brews! I had a long stem bi-metal thermo off by over 8 degrees and too many batches of sweet beer because I used it for mashing.
I recently purchased (for cooking) a thermapen. it is splash resistant, but not submersible, but can be repaired if damaged, and is highly accurate. I compare all thermo temps with this and gives me an extra level of confidence. Check it out.
Holy crap...I am so glad I saw this post.
This weekend I am going to buy a chest freezer/temp controller. It would not have occurred to me that the probe I bought could be such a problem.
I know now.
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@iamwhatiseem You really just need to check it against a couple different known good thermometers. One of the ways I have seen is to put a couple probes in ice water, they should be around 32-34, but all be the same. Then put them in boiling water and all should be around 210-212. Do both extremes because some thermometers will give the correct temp at one extreme but not the other.
So, is there a recommended "waterproof" digital probe thermometer for home brewing? I'm currently using an old (9 yrs) Bayou Classic turkey fryer burner and it is difficult to control the temp as I'm heating/maintaining water temps so I would definitely appreciate an accurate thermometer that I can leave in.
Thank you for this. I've recently started using that same Taylor brand thermometer and my last few batches have been watery. I knew it was temperature related and I was confused, but now I am like well duh... helps to have correct temperature readings. so I just ordered a fancy new guaranteed accurate digital. It was $60 but considering the ton of money I've already invested it makes sense.
AND re-calibrate your instruments before each brew!
I'm still a noob and early on (thank heavens) I discovered nothing could be trusted until it was calibrated. I threw out the Taylor thermometer just like you did - we were lucky not to get sick from under cooked meat.
I compared several thermometers against each other: lab-grade glass thermometer, themocouple, bi-metallic food probe. Only after I trusted the lab-grade did I use it to calibrate others.
I also learned NOT to trust one reading from one point. It can make a significant difference if the fluid is agitated to make it homogeneous, or reading from the top or bottom of the pot.
Your post prompted me to do a little research...and im sure glad! Turns out my themocouple probe isnt meant for immersion. My last 2 brews are coming up really thin and im betting this is why. Good post!
I did a little write-up a while ago on my experiences with thermometers, and my solution (which I'm very happy with):
It's the same company that makes the thermopen, but I feel a little easier to use for all grain brewers.
I'm cornfuzed:
"It had never occurred to me to calibrate my fermenter's thermometer. There is a screw on the back for that purpose. Today I used my trustee Cole-Parmer and it said my wort was 64*F. My fermenter's thermometer said my wort was 69*F, a five degree difference. I also have an analog refrigerator thermometer set on top of the fermenter and it read 64*F. I believe, all this time, I have been five degrees low on everything I have been making."
Since your certified CP and fridge therm agree (64*), wouldn't you conclude that they are correct? And since your uncalibrated fermenter therm reads 69*, 5* higher, wouldn't you conclude that it is 5* high, and therefore you've been correct "on everything you've been making?" How do you conclude that your CP and fridge therm were erroneously reading 5* low "on everything you've been making?" (or am I several* off in my understanding?)
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Thanks so much for the feedback and information. I'm really happy this article helped others out!