How to best measure temperature in a carboy

[Ike]

Couldn't find anything with the search function, so I thought I'd ask.

So, I'm a half-dozen or so batches into homebrewing, and at the moment am fermenting in a 6.5 gal glass carboy, and use a swamp cooler setup for temperature control.

In an attempt to keep an eye on the temperature I'm reaching, I've been using a Polder thermometer tucked between the glass carboy and the shirt that is acting as the swamp cooler. I figure this is about as good as the stick-on thermometer that came with my startup kit; but all that's really telling me is the temperature of the glass carboy and the wet shirt, not the temperature of the wort INSIDE the carboy.

So, what's the best trick to go about actually measuring the temperature of the wort instead of the glass carboy? One thought I had was to find a way to poke the solid thermocouple through the rubber stopper holding the blowoff tube, at least this would let me monitor the temperature of the headspace over the wort, which would surely be a better approximation than what I have now.

As always, THANKS!

 

[FlyDoctor]

Many use a thermometer probe attached to the external wall of the fermentation vessel - whatever that may be. The issue though is that you need to insulate it so its reading the fermenter and not the environment. Cardboard, bubble wrap, all work well. The alternative is a thermowell that puts the probe essentially in contact with the wort itself. I do t have one, but have been toying with the idea. As far as I can tell, the cons are possible contamination, but with good sanitation I don't see this being a big deal.

 

[Punx Clever]

As mentioned before, a thermowell is what you are looking for:
http://www.morebeer.com/products/stopper-thermowell.html

 

[BlueHouseBrewhaus]

I used a piece of packing styrofoam and carved a groove in one side. I lay the grooved side against the carboy and use a couple of mega-huge rubber bands (you could just use tape) to hold it in place. My temp probe slides nicely into the groove and is held securely against the carboy and surrounded by insulation.

 

[wardens355]

Cut some pipe insulation and tape it to the carboy such that it creates a small pocket to push the temperature probe into.

 

[Ike]

I bet I'm too late to worry about insulating the probe for the current batch, but with regard to temperature control I was pretty much going to get what I was going to get from the swamp cooler, knowing true temp would just be a good point of reference for future work and record-keeping. If necessary for the next batch or two I'll insulate the probe as suggested, but I gotta say the thermowell is JUST what I was looking for! Excellent idea, will do!

Ike

 

[Sailingeric]

Digital fish tank thermometer.

 

[lazarwolf]

How are your beers turning out? If they're great, I wouldn't change a thing. If you're getting of flavors that can be specifically tired to high temps or temperature swings, fuesal, banana, etc... then make the change. Therm probe is best put into a two liter of water in your swamp cooler. No risk of contamination and nearly identical Temps.

 

[Ike]

How are your beers turning out? If they're great, I wouldn't change a thing. If you're getting of flavors that can be specifically tired to high temps or temperature swings, fuesal, banana, etc... then make the change. .

I live in Arizona, so while my house is currently 68 degrees (swamp cooler was 63-65 using uninsulated probe this current batch of ale), 9 months or so out of the year it is 75+. Add the heat of fermentation on top of that, and I need to do something. During the hot months, even the swamp cooler doesn't seem to be quite enough: my last batch of ale (an american ale fermented with Notty) had noticeable flavor that (now that I understand a bit more about it) would classify as "hot" flavor. It got better with longer conditioning in the bottle, but it told me I needed to work on temperature control.

Thanks to all!

 

[azazel1024]

Craigslist for a used mini fridge and a temperature controller for it. I happened to have a spare mini fridge laying around (actually two, but I've only converted one) and I bought the parts to make an STC1000 based temp controller for $35.

Been working great for my 3-6 gallon carboys (will fit 1 5/6 gallon carboy or a pair of 3 gallon carboys with a bit of work).

For a swamp cooler/ice bath, thermowell inside the carboy down in the wort is the way to go. For a fermentation chamber, a lightly insulated thermometer on the outside of the carboy works fine.

I've done some quick tests using a sanatized candy thermometer stuck in my carboy versus my STC1000's temp sensor strapped to the side of my carboy with an ace bandage to make it easy to strap on and also mild insulation.

They read within 1 degree F of each other, even during vigorous fermentation. When both are in air, they are within half a degree F of each other. So I'd say that is close enough.

However, with a swamp cooler or ice bath it is a lot harder to properly insulate the thermometer from the actual cooling action.

I've only put 1.5 batches through my new fermentation chamber, but it seems to be working well (and one cold crash, which worked great). My basement though is 63F on the slab in winter and 72F on the slab in summer. A little on the warm side for some ales in the summer, but I haven't had any real temp issues with ales so far (though, I'd prefer repeatable fermentation temperatures instead of "whatever the season brings).

I mostly converted the mini fridge because I wanted to start playing with lagers, and doing ice baths is a PAIN. I've done two lagers pre-real temp control. One was an Oktoberfest which I did in the dead of winter by turning down the thermostat and threatening my marriage so that it was 61F on the slab (and used S23 dry yeast, which seems a bit more warm temp tolerant than some lager yeast), then let it "warm lager" for 10 weeks at 63F (to save my marriage) and then bottle lager through the summer (in the low 70's in my basement) and finally bottle lager in the fridge for over a month from late August until late September before I started drinking it (okay, I tried a couple out of the batch of 30 bottles over the ~6 months).

It was pretty good, but I've had cleaner.

I just did a Dopplebock that I used an ice bath for to keep it at 55-56F for 3 1/2 days before I went on a family trip for 10 days and was able to crank the thermostat in my basement down so that it was 57F on the slab. I then let it sit at 62F for about a week once I got back and was busy/converting my mini fridge. Then it lagered at 42F for a week and then at 35F for a week before I bottled it. I used White labs bock liquid yeast for it.

Tastes very good and clean at bottling, but the ice bath was a horrible pain and I can't really lager using an ice bath.

I just brewed a German Pilsner with WLP830 German Lager yeast and it is bubbling away in my mini fridge at 53F right now. Very excited about being able to do the entire thing with my mini fridge (I did the temp probe comparison with this Pilsner as I was curious). SOOOOOOO much less work than having to swap melted half gallon bottles out of a rubbermaid container half filled with water every 8hrs and then sticking them outside/in my freezer to refreeze. That and now I can properly lager too.

Its cheap and easy. Once you've converted a fridge/freezer, you'll never go back :-D

 

[wardens355]

Once you've converted a fridge/freezer, you'll never go back :-D

Yup. Got three fermentation freezers now, in addition to my serving freezer... my apartment is officially a man cave.

 

[lazarwolf]

I built a fermentation chamber with a garage sale AC unit and a tiny ceramic heater. I am currently the temperature control unit, But I will be upgrading and adding a temperature control unit. I cost me less than $100.00.

 

[azazel1024]

Yup. Got three fermentation freezers now, in addition to my serving freezer... my apartment is officially a man cave.

Waiting on approval from my brother-in-law (IE, no, I don't need my dorm fridge back ever. I am 2600 miles from you, you have to ask? Is the response I am expecting)...then I convert the second mini fridge.

I'd make one big one with a build, but frankly, 1-2 carboys is all I need one to hold, but I'd really like 2-3 in the end. With rare exceptions (like my upcoming "the family is gone, so Daddy will play" week where I am planning 5 brews in 7 days) I generally only have 1 or 2 carboys with something in them. Maybe twice a year I'll have 3 carboys with things in them and maybe once a year we are talking 4-5 carboys/buckets with stuff in them.

Even with the bunch of carboys/buckets, most of them aren't brewed in a short enough period of time that I need them all under temp control still.

2 mini fridges should be enough. I hope. It might end up at 3 some day (at which point, my wife will skin me).

 

[TheMilkMan]

While I do have a temperature controller taped to the side of the carboy, I also use an infrared thermometer gun.

 

[2005STi]

Fermometer strip from Northern Brewer, cheap and easy. Jamil says whatever temp you get on the the outside face of the carboy is within 1/2 a degree of the internal temp of the fermenting wort. Either way it gives you a point of reference. If it's too estery, ferment a few degrees lower than the reading.

 

[azazel1024]

Fermometer strip from Northern Brewer, cheap and easy. Jamil says whatever temp you get on the the outside face of the carboy is within 1/2 a degree of the internal temp of the fermenting wort. Either way it gives you a point of reference. If it's too estery, ferment a few degrees lower than the reading.

That only works if the outside of the carboy is in contact with air. If in contact with water/swamp cooler wrap, it will be inaccurate.

 

[Ike]

Today is brew day, and I have the foam ready to go! And a thermowell is probably going to end up on the "wish list."

Thanks to all!

Ike

 

[RM-MN]

Glass isn't a particularly good insulator. The temperature of the beer on the inside of the glass will be really close to the temperature of the outside of the glass. People who have compared the difference between using a thermowell and just fastening the probe to the outside of the carboy report a difference of about 1/2 degree. Having your probe in contact with the wet shirt and the carboy may skew that a little but I doubt it would be more than a degree, not enough to get excited about. Putting an insulator between the shirt and the probe will get you quite accurate.

 

[Ike]

Yesterday I started five gallons of the brown ale that is a base for the Requiem Raspberry ale everyone loves so much, as well as three individual one-gallon bottles of Edwort's Apfelwein. The Ale Pail (my 6.5 carboy has a scottish ale in primary) and one of the three bottles of apfelwein-to-be each have a Polder thermometer tucked into a pocket made by some foam and what is probably an insane amount of duct tape. No activity so far, but now I have something ELSE to obsess over day after day during primary fermentation! JUST what my OCD needed!

Thanks to all;

Ike

 

[Ike]

OOH WAIT, another question related to this, not something I need to know at the moment but will tuck away for later:

When I make my fermentation chamber (somewhere... over the rainbow...) and I build my controller, it's the temperature from that probe stuck to the fermenter that is the input for the controller, no? I know they're related but for the most part we don't give a hoot what the temperature in the chamber really is, we care only about the temperature of the wort, no?

Another way of asking it: when someone says "I put 5 gallons of blah blah blah in my ferm chamber at 63 degrees" they mean the 63 degrees was the temperature from the probe stuck to the fermenter, not stuck inside the chamber, right?

THANKS TO ALL for suffering the death of a thousand questions as I get the knack of this!

Ike

 

[wbarber69]

OOH WAIT, another question related to this, not something I need to know at the moment but will tuck away for later:



When I make my fermentation chamber (somewhere... over the rainbow...) and I build my controller, it's the temperature from that probe stuck to the fermenter that is the input for the controller, no? I know they're related but for the most part we don't give a hoot what the temperature in the chamber really is, we care only about the temperature of the wort, no?



Another way of asking it: when someone says "I put 5 gallons of blah blah blah in my ferm chamber at 63 degrees" they mean the 63 degrees was the temperature from the probe stuck to the fermenter, not stuck inside the chamber, right?



THANKS TO ALL for suffering the death of a thousand questions as I get the knack of this!



Ike

Usually it's the chamber temp we want to regulate. By changing the chamber temp we in-turn change the temp of the wort inside. Have a way of monitoring both then gives us a differential. Allowing us to see the difference in temperature on the outside relative to the inside can also allow us to monitor fermentation to a point. If you keep the chamber at 63 and the wort stats at 67 then we can reasonably assume that active fermentation is still underway. If the 2 equalize and subsequently the wort temp starts to go lower in relation to the chamber temps then we can surmise that active fermentation has lessened or stalled. Meaning that our yeasties are nearly done. Then you could raise the temperature a bit to force the yeast to "clean up" a bit before deciding to cold crash before kegging/bottling. Check out brewpi.com

 

[RM-MN]

Typically we want to use the probe to measure the beer temperature as that is what matters to the yeast. They don't care if the air outside the fermenter is -20 as long as the beer is the right temperature for them to be comfortable.

 

[azazel1024]

Glass isn't a particularly good insulator. The temperature of the beer on the inside of the glass will be really close to the temperature of the outside of the glass. People who have compared the difference between using a thermowell and just fastening the probe to the outside of the carboy report a difference of about 1/2 degree. Having your probe in contact with the wet shirt and the carboy may skew that a little but I doubt it would be more than a degree, not enough to get excited about. Putting an insulator between the shirt and the probe will get you quite accurate.

It isn't just that it is against the glass, you are going to have a temperature differential through the wort as well, so the parts closest to the glass are going to be cooler than the core of the wort. The more convection going on within the wort, the lower the differential.

I doubt it is going to be off by tens of degrees, but it probably will be off by a degree or two, once the carboy has reached homeostasis. If it is actively cooling down or heating up it could easily be off by more than that.

The temperature differential at the thermometer is a lot more likely to split the difference between the two. If the "cold shirt" is 54F and the carboy is 58F, the thermometer is probably going to read around 56F as an example.