Measuring Fermentation Temperatures

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You hear it over and over again - controlling the fermentation temperature is the key to great tasting beer.
And it's true.
A glorious brew day can be ruined by forgetting about your beer once it enters the fermenter. Don't neglect the cold side!
On this topic I get business school flashbacks of management guru Peter Drucker's famous quote being drilled into my head - "What gets measured gets managed."
So let's talk about measuring your fermentation temps.
Like many things in life, doing a little something is far better than doing nothing. Even just being aware that your fermentation temperatures are important is a step in the right direction. Trust me - not everyone takes this step.
Now you're aware and you start to pay attention. You look at the house thermostat. This is where many brewers (like myself in the early days) go astray because the fermentation temperature can easily reach 10+ degrees F above room temperature.
It's nice and comfy in the 70 degrees F room, but your beer is sweating it out at 80 degrees F.
Thankfully, most homebrewing kits come with these now:

The "fermometer" has saved a lot of beer.
You could brew for years with the fermometer but many homebrewers upgrade to something more accurate and easier to read.
My favorite solution is to use a digital probe thermometer. There are hundreds of these on the market and you can cruise Amazon or HomebrewTalk for reviews.
Personally I use the Therma K from Thermoworks. Pricey but it is a total badass. I review in detail here, but in short, I use it with interchangeable thermocouple probes. The key one for fermentation is a 6.5 ft. heavy-duty wire probe.
The extra long probe is key. I'm sure a lot of you are fermenting in DIY fermentation chambers, freezers/fridges, or the Cool Brewing bag. You want something you can read without opening up your chamber.
My method involves folding up a piece of bubble wrap, taping it down, and then taping the end of the probe to the middle of it. See below:

Then I attach it to the side of the carboy in my chest freezer. First I tried taping the bubble wrap - that sucked. Tape doesn't stick very well to a carboy and if you do get it taped on, there are usually remnants when you remove it.
After getting fed up I noticed some bungee cords nearby, and my problems were solved:

A bungee cord is fantastic for attaching your probe to fermenters. They stretch for larger fermenters and can be knotted for smaller ones. Use them.
With the probe securely in place I can now easily check my temps without opening the freezer:

(If you're using a temperature controller you can use this same technique with its probe. Personally I put mine near the bottom of the freezer because I found it overshoots the target temperature when attached to the fermenter.)
This method is very accurate. It reads within 1-2 degrees F of the actual beer temp.
A thermowell is another way to measure the temperature. The probe goes into a long tube that is submerged in the fermenting beer. It works but I find it unnecessary and not any more accurate than the probe taped to the side.
Don't think you need to go for the fanciest and most expensive solution right off the bat. As I said above, just start to measure your temps and you're on the way to better beer.
Billy Broas heads up The Homebrew Academy, where you can find tips, videos, and online courses for brewing world-class beer at home. He's co-author of the book Craft Beer for the Homebrewer, a certified BJCP beer judge, and his beer philosophy is that "we should all be beer geeks, not beer snobs."
I do have those tape thermometers on my carboys still. But I purchased two 16" thermowells ($12 each) (I only use 2 fermenters) and a few of those real cheap ($1.50) Chinese digital thermometers with the remote sensor. Total cost less than 15 dollars. The thermowell fits right into the center attachment of a standard rubber carboy hood and I use the offset attachment for my blow off hose. I tested the thermometers against my good one and they are accurate. Even if they weren't I could fudge the reading. When my fermentation closet gets colder I substitute the thermometer probe with the thermocouple probe for a cheap stc 1000 type controller ($13) attached to a heat wrap. The heat wrap is 12" heat tape from the pet store and sold for $3.00 a foot. You can have quality fermentation temp control the cheap.
I did use the bubble wrap trick at first but it was a pain in the butt.
I attach my STC-1000 temp probe directly to my carboy. Insulate with a little piece of neoprene. Seems to work well for me the last few years.
I used the Mini-Thermocouple from Thermoworks with a couple different probes. I like the fast read times and variety of probes for different applications. I have a metal probe that I use when measuring the mash in temp and pitching temps, then the same wire probe to measure temp throughout mash in my cooler and fermentation.
I have been thinking about this for a while, but I often brew two batches at once (two different beers between 5-10 gallons each)and didn't want to buy two thermometers. However, based on the discussion, I got the Two-Channel Thermocouple with Alarm and will be able to measure and track both mashes!
Now it will be a breeze to take measurements at 15 min intervals (or less if I get the 10-20 minute mash down)...
i use an ace wrap to attach my probe. no muss no fuss. and you can just tuck the probe into it so no bubble wrap.
I'm not sure I understand from the images, the probe is fully covered in bubble wrap? How accurate can it be if it's not touching the fermentor?
I'm a fan of this Tac 'N Stik putty from Elmers, personally. It sticks to the carboy/bucket/whatever and doubles as insulation. The best part is that it's reusable! I've been using the same pack for the last two years.
I use a STC-1000 in a chest freezer and attach my probe exactly as described here (bubble wrap and bungee). It has worked very well for me and my beers have gone from good to great adding fermentation temp control. I recommend this in front of the long list of things most new brewers are faced with, even before the bigger pot!
I monitor my chamber temp on my STC-1000 and my probe is in a water bottle. It does take a fairly long time to change the temperature of a 5 plus gallon container of liquid. My thougth are if you place the container (carboy) in a chamber of X temperature, that is the best you can do on a home brewers budget (not having direct cooling). The two temperatures will affect each other till there is an equilibrium adn that is effected by the chamber temperature. Am I missing something?
I've been using STC-1000 to run a fan and a paint can heater, keep cold using frozen water bottles. Today I added an extra probe to the Rasp Pi watching over my keezer, now I'll never get surprised with temp swings.
I just cut up a spare bottle koozie and tape it to the side of the fermenter with the probe on the inside. The koozie insulation works fine and so far all beers from the chamber have come out clean.
I've used the outdoor sensor with six foot wire from an indoor/outdoor digital thermometer to measure the temperature inside the fermentation chamber I built. I used a piece of Styrofoam carved out a cavity for the probe to sit flush in and tape the block to the center of the fermentor, works like a charm.
@SeeMont - what you really want is to measure the temperature of your beer, not your chamber, right? If your yeast suddenly takes off and goes crazy and raises your beer by several degrees, you wouldn't want to wait until it radiates enough heat to warm up the temperature elsewhere - you'd want to chill that sucker down immediately.
That's why measuring your fermenter (by using a thermowell or taping the probe to it with some insulation) is preferable.
@QuercusMax I do the same as @SeeMont. I usually have two beers in my fermentation chamber at the same time....So I do want to maintain the temp of chamber than than just following the trend of a single beer. I haven't had any issues, even with finicky yeast... I do ferment in plastic so the temp change is more analogous to the water bottle the probe is in....If you have two different yeasts in primary that need roughly the same temp in a single chamber, what's the best course of action?
Excellent writeup! It couldn't have come at a better time. I just picked up my chest freezer and ordered a temp controller to run it.
@boicutt The prob isn't fully covered. It's exposed so it presses directly against the fermenter. The bubble wrap just insulates it so it gets an accurate reading of the beer temp.
I use 2 3 gallon Better Bottles to ferment and place my STC1000 probe between the two bottles in the indentations at the bottom. I keep the bottles squeezed tight together. I've tested in the obvious way. On a hot summer day I can open my fridge and the controller's readout doesn't budge. I've made some pretty tasty lagers this way.
I'm also using the STC-1000 probe attached to the side of the carboy with some bubble wrap for insulation. Seems to work well although I've always wondered whether it would be more accurate to put a thermowell down the carboy cap and put the probe down the thermowell? Thouhts?
I like the use of bungie cords to secure the bubble wrap, btw. After wrestling with tape for so long - why didn't I think of that? lol
Curious. Is anyone measuring temperatures from some kind of electronic device that logs temperatures to disk? I'm interested in reviewing long term temperature trends, as opposed to point-in-time measurements.
A few batches ago I had my probe taped to the side of the carboy but some condensation on the carboy and the tape wouldn't stay on. I was standing there looking at it wondering what to do, looked around and saw a bungie cord... Been using it for a few months. I guess we homebrewers think alike.
What do you mean by this comment?
"(If you're using a temperature controller you can use this same technique with its probe. Personally I put mine near the bottom of the freezer because I found it overshoots the target temperature when attached to the fermenter.)"
I thought you were attaching your probe to the fermenter?
All this time, I've thought my 65 degree basement was perfect for ales. Lager's I understand have to be much lower temps. Is there a chart on here that matches type of brew, type of yeast, and target temp?
What are the bad things that happen if ale temp is too high? Lager?
Should everyone have a fermentation chamber??
Thanks, good read.
@Skiffy Sorry, it's kinda confusing because I'm talking about two different probes here - the thermometer probe and the temperature controller probe. The one I put near the bottom of the freezer is the temperature controller probe. The thermometer probe is the one I attach to the fermenter.