# Measuring Fermentation Temperature



## popmedium (8/12/13)

Hey mates,

Just wondering how you guys measure fermentation temp?

I cut up a stubby cooler, tape it to the side of my fermenter and stick my temp probe in there. 

I actually measured the temp of the fermenting wort the other day (well after primary, most activity had died down) and was surprised to see that although my temp probe read 19 C, the temp of the fermenting wort was 22 C! What the heck would the temp be during the night of activity!?!?!

Keen to hear your thoughts. 

Joel


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## manticle (8/12/13)

I have my probe attached to the cube with tape and softlon foam but I always set the stc about 2.5 degrees below intended temp for the first part to allow for heat generation and plastic insulation.

Well I did before my fridge died.

Have measured actively fermenting wort previously and usually find it's around 2-2.5 degree higher than stc reading.


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## Ducatiboy stu (8/12/13)

Your probe needs to be in the wort. Tapping it to the outside gives a false reason due to

A. The plastic of the ferm acts as an insulator

B. You are also measuring the outside ambient air temp along with the temp of the plastic.


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## indica86 (8/12/13)

Do you do that Ducati?


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## Ducatiboy stu (8/12/13)

I have, but not as a rule. Adds an element of infection ingress. Generally you will find the wort temp to be within a few degrees of ambient temp. So the cooler place the better for your ferm. I have measured peak ferment temps 4-5*c higher than ambient. 

Personaly, I dont bother measuring any more. So dont loose sleep over iy


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## elcarter (8/12/13)

One option is to piss of the air lock and glad wrap the top of the fermenter.

Stc 1000 probes are apparently water proof 

Lost one a while back and froze a lot of beer so I'm not so sure these days.

Drop Sensor into wort for bang on temp.

This of course would need to be sterilized and what ever plastic is on the wires would be in contact with the wort.

I guess if you were that particular you'd be fermenting in stainless with a pt 100 in direct contact and broke.


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## Rubix (8/12/13)

Stainless steel well in the lid of the fermenter and just drop the stc probe in. Easy to steralize and accurate.

http://shop.beerbelly.com.au/equipment/fermenting/fermentor-thermowell-9-53mm-x-400mm-stainless-steel-with-grommet.html


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## Glot (8/12/13)

I just have a thermocouple sensor in each fermenter and plug them into my thermometer when I want a reading. I just sanitize them and then seal the cling wrap lid over them with insulation tape.I have the temp controller probe taped to the side of the fermenter but insulated from air temp. I set the fridge thermostat just a bit cooler than my required temp so I have a back up minimum temp.


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## jotaigna (8/12/13)

I stick my probe outside the fermenter with a strap and bang in a lot of insulating foam on the other side of the probe.
The downside: 1 to 2 degrees lower than inside fermenting temperature in the first 48 hours (ale) of fermentation.
The upside: easy to do, no risks of infection and it is repeatable i.e. it is always the same so set your temp control for 1 to 2 degs lower than the desired fermentation temp for good results.

On a side note, I find that the only time that 0.5C precision is needed is when you aim for(or leaving out) certain ester characters in beer. i.e. belgians and german wheat beers.

For lagers if you ferment between 10-12C there is no (major) difference, so high precision is not that warranted
For west coast ales 17 to 19C is fine and for english ales 18-20C.
In summary, an approximate setting with rule of the thumb adjustment will produce acceptable results, without much fuss.

How to arrive to a rule of the tumb? get a couple of thermometers: one in the fermenter properly sterlisied, one in a glass of water next to the fermenter, your probe stuck to the side of the fermenter. Note the readings on all three quite often (3 hours) during active fermentation and less so (12 hours) during the final stages of attenuation.
This will give you a clear picture of the differences, and then you can sleep easy anyhow.


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## lael (8/12/13)

Rubix said:


> Stainless steel well in the lid of the fermenter and just drop the stc probe in. Easy to steralize and accurate.
> 
> 
> Rubix, I was looking at getting some of these. What is the bottom made of? Have you tested the reported temp vs putting the probe against the side of the fermenter?
> ...


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## verysupple (8/12/13)

I drilled a hole in the lid of my fermentor and put in a cable gland. The ST-1000 probe get's sanitised and goes though that straight into the wort and works brilliantly. I prefer it over a thermowell because it's cheaper and I can adjust how low it hangs for doing different sized batches.


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## Spiesy (8/12/13)

It's super cheap and easy to buy a thermowell and then submerge your temp probe into the middle of the wort for an accurate reading... kind of puzzles me why people cut corners and choose to do either tape something to the side of a fermenter, or measure the temp of an inactive body of liquid elsewhere in the fermenting chamber... but, each to their own...


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## popmedium (8/12/13)

Thanks mates!

So, one of three options:

1. Live with it
2. Do some experiments with fermenting wort and get an average temperature differential
3. Use a thermowell (I smell a DIY project coming on!)

thanks a bunch everyone!


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## Ducatiboy stu (8/12/13)

I would say all 3


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## Rubix (9/12/13)

Lael, it's all stainless mate. Haven't played around taking temps from the side vs the thermowell. Might see if i can get a bit of free time tomorrow and test it out and report back.


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## zarniwoop (9/12/13)

Correct me if I'm wrong on this but doesn't the fermentation, particularly in the first few days, create heat? If so by using an offset then wouldn't the temperature be correct whilst the wort in generating heat but once the primary fermentation is over it will stop generating heat, will reach equilibrium with ambient and the temperature will now be incorrect owing to the offset?

FWIW I just tape the NTC probe to the outside of the fermenter, I don't even bother with foam. The fermenter is in a fridge and has such large thermal mass that even if the temperature that the probe measures increases a couple of degrees when I open the door in comes back down again very quickly long before the fridge can kick in and start cooling.

I should probably put a thermowell in or dangle a waterproof sensor in the wort as there will be some temperature differential especially when the wort is creating heat but I tend to rely more on the insulating capacity of the fridge to mean that the temp on the outside of the fermentor is similar to the wort temp.

BTW although you'll probably get away with dunking the STC-1000 probe in the fermenter I'm not sure it will do a lot for it's lifetime and it may even affect the accuracy of the reading if the sensor gets wet (parallel resistances etc - but I need to think about that), you'd be better off buying a waterproof sensor from ebay, I haven't used these but the specs are so close that they should work fine:

http://www.ebay.com.au/itm/5Pcs-NTC-10k-1-3470-Temperature-Temp-Sensor-Probe-Thermometer-Waterproof-/300961133754?pt=AU_B_I_Electrical_Test_Equipment&hash=item4612ae74ba

Cheers

Zarniwoop


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## Kingy (9/12/13)

Stainless probe into the wort set the controller temp. Sleep well at night, never worry at work.


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## verysupple (9/12/13)

zarniwoop said:


> BTW although you'll probably get away with dunking the STC-1000 probe in the fermenter I'm not sure it will do a lot for it's lifetime and it may even affect the accuracy of the reading if the sensor gets wet (parallel resistances etc - but I need to think about that), you'd be better off buying a waterproof sensor from ebay, I haven't used these but the specs are so close that they should work fine:
> 
> http://www.ebay.com.au/itm/5Pcs-NTC-10k-1-3470-Temperature-Temp-Sensor-Probe-Thermometer-Waterproof-/300961133754?pt=AU_B_I_Electrical_Test_Equipment&hash=item4612ae74ba


STC-1000s are sold as aquarium temp controllers....I'm pretty sure the probe is _properly _water proof. I also check the calibration every couple of months and it hasn't changed over the year I've had it.


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## jaypes (9/12/13)

Yes, fermentation is an exothermic reaction so if you want to ferment at 18 Degrees and the yeast strain you use actually bumps this up to 20 degrees then you can adequately compensate.

Reality is that you cannot predict what this number will be due to yeast strains, health and quantity of yeast and how active the ferment is.

Saying that, I just tape a foam block over the sensor and set to 18 for my ales, pretty good drinking IMHO but YMMV


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## breakbeer (9/12/13)

Extra hole drilled in the lid, probe dropped into the wort & good old gaffer tape to seal it

I prefer to measure the temp of the actual wort rather than the plastic holding it


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## manticle (9/12/13)

zarniwoop said:


> Correct me if I'm wrong on this but doesn't the fermentation, particularly in the first few days, create heat? If so by using an offset then wouldn't the temperature be correct whilst the wort in generating heat but once the primary fermentation is over it will stop generating heat, will reach equilibrium with ambient and the temperature will now be incorrect owing to the offset?


The early part is when it's most important.

I usually start my wort about 4 degrees below intended temp, set it to around 2.5 below once pitched then often bring it up a degree or two when it's close to FG. Rest it for a few days then down to fridge temps to cold condition.

I measure the actual wort every so often to see if I'm in the ballpark - as easy as dropping a thermometer into a hydrometer tube (unless you're outside in the snow).


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## bradsbrew (9/12/13)

I found that the STC probe in a PET bottle of water sealed with blue tack and placed against the fermenter works well. That way you get to measure the temperature of the liquid and not the air.


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## stm (12/12/13)

I just let the probe hang near the top of the fridge and let it measure the air temp, and set it about 3 degrees below my target fermenting temp. This produces the smallest temp variation in the wort/beer with the equipment I have (fridgemate). As fermentation completes (ie, exothermic phase completes), the beer temp slowly drops to about what the fridgemate is set to.


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## Dips Me Lid (12/12/13)

I've been thinking about this topic all week, at present I use a Hevac HTC-2 heat/cool controller with a standard Hevac sensor stuck to the outside of the fermentor to control the fridge/heatband. I've been looking to tighten my control on the actual temp of the liquid, 
A thermowell looks like a good option to get a more accurate reading of the liquid but it seems accuracy can be a problem for an incorrectly sized thermowell, looking at this entry from wiki;

"To be representative of the average temperature of fluid, the thermowell must extend a few percent of the inside diameter of the process pipe or vessel. [1] A rule of thumb that is sufficient for most industrial applications (apx. 1% accuracy) is to ensure that the thermowell projects 5 times its own diameter into the process plus the length of its sensing element. So, for a grounded thermocouple spring loaded into a thermowell with a 1 inch diameter shank and a tip thickness of .25" a typical immersion length would equal 5.5 inches (1" OD x 5 + .25" well tip thickness +.25" sensor wall thickness = 5.5"). 

Apx. 1% accuracy by that rule sounds pretty good, are there any other downsides to thermowell's? Increased sanitation risk ect?


,


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## verysupple (13/12/13)

That quote is simply about how quickly the thermowell and probe can get to thermodynamic equilibrium (or near enough) with the liquid. It's about systems where the temperature may change rapidly such as if you had a thermowell in a pipe where the liquid flowing through it can change quickly. For fermentation the temperature changes very slowly and this really isn't an issue.

The only minor issue with using a thermowell I can think of is if the inside diameter of the thermowell is significantly larger than the probe such that the volume within the thermowell (which would be mostly air) never reaches thermodynamic equilibrium with the wort. That's hopefully unlikely though.


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## Dips Me Lid (13/12/13)

That makes sense, a static liquid wouldn't pose the same issues, in regards to the deadspace between the inside of the thermowell and the probe I guess Heat transfer paste would work as a good conductive medium between the two.


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## Parks (13/12/13)

joel connolly said:


> I cut up a stubby cooler, tape it to the side of my fermenter and stick my temp probe in there.


This is exactly what I do for these reasons:

1. Measuring the actual wort temp is only beneficial at the start of the ferment when it's really generating heat. After that point you are deliberately fluctuation your temp 2 degrees around your set point.

2. Measuring air temp means unnecessarily turning your fridge on and off when you open the door.

3. Measuring a bottle of water in the fridge doesn't address wort temp at all. This option I use in my kegerator.

Ideally you would measure wort temp first then switch to something more suitable. Or have a temp controller that could turn on/off more tightly than 1 degree.


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## manticle (13/12/13)

Or just pitch cool and allow gentle rising through ferment. Easy done, works well for me.


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## Parks (13/12/13)

manticle said:


> Or just pitch cool and allow gentle rising through ferment. Easy done, works well for me.


See I struggle to get my wort below 25 degrees with the chiller. I'll try to sort out a post chill ice pump thing one day...

Anyway my point is that I either wait to pitch another 2-3 hours to get from 20 to 16 or whatever or I pitch and wait it out. Lots of things to think about...


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## manticle (13/12/13)

Easier for no chill I guess.


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## Coalminer (13/12/13)

manticle said:


> Easier for no chill I guess.


I normally no-chill and usually put the cube in the fermenting fridge set at the desired pitching temp - after a couple of days its ready to pitch

Whats wrong with one of these: -

http://www.craftbrewer.com.au/shop/details.asp?PID=955

They fit into an airlock grommet and connect to an stc-1000 - not expensive in the grand scheme of things

I am considering using one of these and I think it should be placed half way between the side of the fermenter and the centre to get an average reading

cheers

edit -spelling and hyperlink


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## djar007 (13/12/13)

I also use a jar filled with water to put the probe in. Less reactive if I need to open the door. I set it up at temp the day before so I can put the fermenter straight in. Always wrestle with the pitch too warm and stress the yeast v's wait for wort to be chilled to temp and risk an infection dilemma. Usually get it chilled close to temp and those few degrees over soon drop down in the fridge I have so I can live with myself pitching a couple of degrees over. For now anyway.


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## Parks (13/12/13)

Coalminer said:


> Whats wrong with one of these: -
> 
> http://www.craftbrewer.com.au/shop/details.asp?PID=955
> 
> I am considering using one of these and I think it should be placed half way between the side of the fermenter and the centre to get an average reading


My argument against using something like this is you *guarantee* a temperature swing _in your wort_ up and down a total of 1 to 2 degrees (for 18 degrees it'll go down to 17, up to 19, down to 17 etc).


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## Dips Me Lid (13/12/13)

Is there any data available on the average amount of heat yeast produce during primary fermentation? I realize this could probably vary a lot due to a number of reasons but is there a ballpark figure for aerobic/anaerobic phases?


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## manticle (13/12/13)

All yeasts are different. I mostly operate on a 2.5 degree swing based on measurements I've taken but just like some humans can run faster than others, some yeasts can produce more or less heat than others.

Apart from that- wort gravity and composition, yeast health, yeast numbers, fermentation vessel and environment will create other important variables.


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## Dips Me Lid (13/12/13)

Cheers mate, I thought there would be a lot of variables and hence no easy answer, 2.5 is a good start point though. What are common commercial brewery practices for measuring fermentation temp? I guess they have tighter deadband control and measurement than homebrewers have access to.


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## O-beer-wan-kenobi (13/12/13)

Im going to add my 2c worth.

if you have a temperature controller that has a differential setting of say 0.2 degrees, you can measure the wort directly and will only get the 0.2 degrees fluctuation either side of your set temp.

I had a fridge temp controller that only had 1 degree differential, which like Park said, would give you a fluctuation from 17 to 19 degrees if your set temperature was 18.

I now use a temp controller set at 0.2 degrees differential to measure the wort and keep tighter temp control. I was concerned that there was too much fluctuation for the yeast which could stress them or maybe stall if you were fermenting on the high or low end for the yeast strain.


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## Spiesy (13/12/13)

verysupple said:


> The only minor issue with using a thermowell I can think of is if the inside diameter of the thermowell is significantly larger than the probe such that the volume within the thermowell (which would be mostly air) never reaches thermodynamic equilibrium with the wort. That's hopefully unlikely though.


I drop the probe in so that it hits the end of the thermowell (which is positioned in the middle of my 30l fermenter, and goes down about halfway). Stainless on stainless - I'd imagine that translates a reasonably accurate temperature of the surrounding wort.


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## jkeske (13/12/13)

I know this site thrives on conjecture and hearsay, so I hope I don't break the mold with posting actual data. But yes yeast is exothermic (heat generating) during fermentation, and can raise the fermentation temperature buy several degrees over the ambient temp. The attached examples were done in a chest freezer controlled by a brewpi (www.brewpi.com). The wort temperature during early ferment is significantly higher then the surrounding air. A fan in the freezer would have probably equalized the temp a bit, but it clearly shows that where you are measuring your temp makes a difference


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## djar007 (13/12/13)

That is awesome jkeske. Says it all. Now I am rethinking the glass of water with a probe in it. Because obviously a glass of water is not equal to a glass of fermenting wort. Pretty obvious I guess.


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## lael (14/12/13)

jkeske said:


> I know this site thrives on conjecture and hearsay, so I hope I don't break the mold with posting actual data. But yes yeast is exothermic (heat generating) during fermentation, and can raise the fermentation temperature buy several degrees over the ambient temp. The attached examples were done in a chest freezer controlled by a brewpi (www.brewpi.com). The wort temperature during early ferment is significantly higher then the surrounding air. A fan in the freezer would have probably equalized the temp a bit, but it clearly shows that where you are measuring your temp makes a difference


Site thrives on conjecture  - remember reading a similar comment in how to brew and laughing.

Do you use one of the brewpi's?


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## verysupple (14/12/13)

Dips Me Lid said:


> That makes sense, a static liquid wouldn't pose the same issues, in regards to the deadspace between the inside of the thermowell and the probe I guess Heat transfer paste would work as a good conductive medium between the two.


Maybe that'd work, although the only thermal paste I'm used to working with is for computer CPUs and that's designed to be used in a very thin layer, not a thick clump. If you had some industrial type paste (if that exists) that might work. 

I think the best solution is to simply get a thermowell that's the right size for you probe.


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## verysupple (14/12/13)

Spiesy said:


> I drop the probe in so that it hits the end of the thermowell (which is positioned in the middle of my 30l fermenter, and goes down about halfway). Stainless on stainless - I'd imagine that translates a reasonably accurate temperature of the surrounding wort.


Yeah, that should work fine because the probe and thermowell _should_ be in equilibriuim. The issue is if you're relying on air to transfer heat between the thermowell and probe.


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## bmarshall (15/12/13)

Does +/- 1 deg really make much difference?


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## Ducatiboy stu (15/12/13)

Not really if you get it below 18-20*c. 

Remembering that the yeast will create it own heat.


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## verysupple (15/12/13)

bmarshall said:


> Does +/- 1 deg really make much difference?


If it's _consistently _1 deg out then it's not a problem. You can adjust the ferment temp up and down as required to get the desired result. If it's not consistent then it does make a difference. 

If you have your probe stuck to the outside of the FV and it consistently reads 1 deg lower than the actual temp then that's fine. However on the homebrew scale, no two ferments ever create the exact same amount of heat at the exact same rate, so the error in the measurement will be different for every ferment. The problem comes when you actually have no idea what the real temp is.


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## bmarshall (16/12/13)

There couldnt be drastic differences in ferment temp from different varieties of yeast and amount of sugars in the wort for homebrew volumes. Commercial volumes may vairy a bit though.
Be good to see a small and large volume ferment with same amount of sugars, and two with same volume ferment with different amount of sugars. Then vice versa with yeast varietys.


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## Dips Me Lid (16/12/13)

verysupple said:


> Maybe that'd work, although the only thermal paste I'm used to working with is for computer CPUs and that's designed to be used in a very thin layer, not a thick clump. If you had some industrial type paste (if that exists) that might work.
> 
> I think the best solution is to simply get a thermowell that's the right size for you probe.


Yeah I'd agree the right sized probe for the well is paramount, industrial type pastes are available for this use as well, not sure what the losses from direct contact between metals to contact via heat transfer paste would be, but I'm guessing the accuracy would be close enough.


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## superstock (19/12/13)

I was doing an experiment today with using different materials for the swamp cooler covering and only had water in the fermenter, so I pulled the temp probe out of it's insulated (wet suit ) pocket on the side of the FV and dropped it through the airlock hole into the water. The result------- in the pocket 21.7'c, in the water 21.8'c-------so it seems to me that a temp probe in a well insulated & tightly fitting pocket reads the wort temp pretty accurately.


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## breakbeer (22/12/13)

I still find it hard to believe that people aren't measuring the temp of the actual wort & rely on a small bottle of water or something taped to the side of the fv

If you're gonna do something, do it properly


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## Glot (22/12/13)

An interesting concept. Actual data. Sorry.


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## vortex (22/12/13)

superstock said:


> I was doing an experiment today with using different materials for the swamp cooler covering and only had water in the fermenter, so I pulled the temp probe out of it's insulated (wet suit ) pocket on the side of the FV and dropped it through the airlock hole into the water. The result------- in the pocket 21.7'c, in the water 21.8'c-------so it seems to me that a temp probe in a well insulated & tightly fitting pocket reads the wort temp pretty accurately.


So it should. The wall of the fermenter will equalise with the wort temp pretty quickly.

That said, I have a thermowell in my wort - though I didn't notice much difference between that and when I sat the fermenter on it.

New fermentation controller will have graphs and logging. Data geek wants to know.


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## lael (22/12/13)

Would love more data from people that have thermowells / place the probe in the wort. Fascinating they were only marginally different.


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## Scooby Tha Newbie (22/12/13)

Nice thread good info. I will go with the stubble cooler on the out side idea (2.5deg less than ferment temp dialed in). Easy simple and ticks all the boxes


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## beerkravin (22/12/13)

is measuring the ambient temperature of your fermentation area (read: fridge) less ideal than measuring the temperature of the wort itself?
measuring the ambient requires something to activate the heat\cool cycle. If the fridge itself is chilling the wort, then what's heating it back up?
The temperature outside the fridge. the heat provided by the ferment itself. the heating side kicks in to balance it out. yeast doesn't like a lot of fluctuation, a stable warmer temp or a stable cooler temp will give you more consistency.

Ambient
Fridge cools ambient > When Ambient hits desired temp > cooling stops > drops below ambient > heating starts > start again.

the logic in this involves 'Thermal Dynamics'. while the ambient temp can fluctuate back and forth quite rapidly, the mass of the wort will fluctuate much slower keeping it more stable. or for a simple analogy if i had boiling hot water and freezing cold water and sprayed you with each alternately fast enough, it would mostly feel warm to you because your body needs time to heat or cool accordingly, somewhere in the middle is 'warm'

Wort
Fridge cools ambient > ambient cools wort > wort hits desired temperature > Cooling stops > Drops below ambient > heating starts > start again

the difference here is that second step, "ambient cools wort". if I freeze something, or heat something, both the cool and the heat need to penetrate the mass to heat or cool it evenly. while fermenting, your wort is spinning, stirring and being circulated by the yeast, but that's still a lot of mass to heat or cool to hit temperature.
the fridge will keep cooling until the mass is at the ideal temp, but in doing so, theoretically the ambient would be cooler than the mass due to the fridge still running while we're waiting for that mass to cool. the same goes for the heat.

so what you have with ambient is fast temperature swings back and forth, which I think would be slower, but much more gentle at raising or lowering the temperature of your wort. with measuring your wort, you'll get to the temperature quicker but you'll probably find there will be bigger swings while the heating and cooling kicks in and out adjusting the mass of 23+L of wort.

if you can get your wort to the temp you want BEFORE you pitch your yeast, i think the difference between the two is negligible as once you reach that desired temp, fluctuations are going to be minor either way you choose. probably be easier to split hairs.

to test it you would need two calibrated thermometers. one to measure the ambient and one to measure the wort, monitoring the differences between the two.
i would be surprised if the difference was +/- 2C


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## zarniwoop (22/12/13)

OK at the risk of putting some further science in this...

We're basically dealing with a thermal system here with the wort the being both the heat source and the target measurement point. As you move further away from the wort through various materials (side of the fermenter wall, stainless steel thermowell etc) you will encounter thermal resistances of varying values, if the wort is generating heat then as you pass through each resistance the temperature will drop as some of the heat is absorbed by this interface (resistance), how much it drops will depend on the level of resistance and how much heat energy is passing through it, but the better the conduction properties of the interface the less temperature drop, i.e. if the wort is 25C and generating heat then it might be 24C on the other side of a metal thermocouple with thermal paste but only 23C on the other side of a plastic fermenter. Once the wort stops generating heat the difference will be significantly lower as they will reach thermal equilibrium as there is no heat energy coming from the wort to generate a thermal difference across the interface. There may be a slight difference owing to the varying insulating levels of the fridge.

Bottom line when the wort is generating heat you're better off measuring the actual wort, when it's not it probably doesn't matter.


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## Glot (22/12/13)

But that takes all the voodoo out of making a good beer 
A good clear explanation though.


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## O-beer-wan-kenobi (22/12/13)

So if heat rises, is the top part of then wort warmest or the bottom?
If it is bottom fermenting yeast is the bottom warmest?
What position should the temperature be taken? Top, middle, bottom?


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## lael (22/12/13)

Yeah, that's why I'm interested in hearing more from people who actually have the thermowells. I'm guessing there is a difference in from the steel, but realistically I doubt any people have managed or attempted to get thermal paste to the end of a long narrow tube ( good luck...) Which means the air inside the thermo well also acts as an insulator too, right?

So, I'm curious to hear from more people what the temp is inside the thermo well, taped to side under insulating material (foam/neoprene sound like the most common) and directly in the wort (with great sanitisation of course!)

Any other people have them?


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## zarniwoop (23/12/13)

Sadly I no longer have access to multi-channel temperature data loggers or else I could have stuck probes all over/in my next batch. Anyone else got any kit?


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## beerkravin (23/12/13)

is measuring the ambient temperature of your fermentation area (read: fridge) less ideal than measuring the temperature of the wort itself?
measuring the ambient requires something to activate the heat\cool cycle. If the fridge itself is chilling the wort, then what's heating it back up?
The temperature outside the fridge. the heat provided by the ferment itself. the heating side kicks in to balance it out. yeast doesn't like a lot of fluctuation, a stable warmer temp or a stable cooler temp will give you more consistency.

Ambient
Fridge cools ambient > When Ambient hits desired temp > cooling stops > drops below ambient > heating starts > start again.

the logic in this involves 'Thermal Dynamics'. while the ambient temp can fluctuate back and forth quite rapidly, the mass of the wort will fluctuate much slower keeping it more stable. or for a simple analogy if i had boiling hot water and freezing cold water and sprayed you with each alternately fast enough, it would mostly feel warm to you because your body needs time to heat or cool accordingly, somewhere in the middle is 'warm'

Wort
Fridge cools ambient > ambient cools wort > wort hits desired temperature > Cooling stops > Drops below ambient > heating starts > start again

the difference here is that second step, "ambient cools wort". if I freeze something, or heat something, both the cool and the heat need to penetrate the mass to heat or cool it evenly. while fermenting, your wort is spinning, stirring and being circulated by the yeast, but that's still a lot of mass to heat or cool to hit temperature.
the fridge will keep cooling until the mass is at the ideal temp, but in doing so, theoretically the ambient would be cooler than the mass due to the fridge still running while we're waiting for that mass to cool. the same goes for the heat.

so what you have with ambient is fast temperature swings back and forth, which I think would be slower, but much more gentle at raising or lowering the temperature of your wort. with measuring your wort, you'll get to the temperature quicker but you'll probably find there will be bigger swings while the heating and cooling kicks in and out adjusting the mass of 23+L of wort.

if you can get your wort to the temp you want BEFORE you pitch your yeast, i think the difference between the two is negligible as once you reach that desired temp, fluctuations are going to be minor either way you choose. probably be easier to split hairs.

to test it you would need two calibrated thermometers. one to measure the ambient and one to measure the wort, monitoring the differences between the two.
i would be surprised if the difference was +/- 2C


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## TSMill (24/12/13)

Spiesy said:


> It's super cheap and easy to buy a thermowell and then submerge your temp probe into the middle of the wort for an accurate reading... kind of puzzles me why people cut corners and choose to do either tape something to the side of a fermenter, or measure the temp of an inactive body of liquid elsewhere in the fermenting chamber... but, each to their own...


I didn't have a good answer, so I bought the beerbelly thermowell within 5 minutes of reading this. Installed today and on its maiden run.


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## zarniwoop (24/12/13)

beerkravin said:


> is measuring the ambient temperature of your fermentation area (read: fridge) less ideal than measuring the temperature of the wort itself?
> measuring the ambient requires something to activate the heat\cool cycle. If the fridge itself is chilling the wort, then what's heating it back up?
> The temperature outside the fridge. the heat provided by the ferment itself. the heating side kicks in to balance it out. yeast doesn't like a lot of fluctuation, a stable warmer temp or a stable cooler temp will give you more consistency.
> 
> ...


I think you're probably right but my only concern with measuring ambient is that the accuracy will be questionable whilst the wort is producing heat, ie loss of heat between wort and outside of the fermenter, it may work if your measured and used an offset during this period.


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## Kingy (24/12/13)

Stainless steel probe into the wort for accurate reading on a 1 degree swing for on/off times. If you gunna have a dedicated fermentation fridge why not do it properly and be incontroll of the wort temp. I think the probe and controller is only about 75 bux all up. Small price for the benifits.
I can't believe how many people have a ferm fridge and arnt measuring the actual wort.


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## beermeupscotty (25/12/13)

*jkeske*, awesome data! Great reference for those looking at temperature measurement and considering getting a thermowell (i.e. me ).

I'm establishing a new setup with temp control, and looking at your data, seeing the dT between the two measuring points, I thought I might forego the thermowell for now and instead just measure the side of FV and add an offset to the beer temp setpoint. However, the dT seems to change depending on the steadiness of the wort temperature. As the wort temp settles, the dT decreases as the two temps equlibrate, as zarniwoop and manticle mentioned. As others are suggesting, looks like it's worthwhile just to do it right (accurately) and be done with it, so I think I will get a thermowell.

That brewpi is sweeeeet - I'd love to have a setup like that. :beer:

I have a few questions/comments about the charts/brewpi setup:

1) To clarify, do you have two probes simultaneously feeding data into a multi-channel reader (i.e. one for beer, one for fridge)?

2) Sorry if I've misunderstood, but reading your chart comments... are you suggesting the oscillations are due to measuring *air *(temperature) rather than _liquid_, and that using a thermowell (with probe in liquid) allows for smooth recording changes in temp (as seen in second chart)?

If it were the influence of air temp causing the oscillations, the oscillations would be present for the 'Fridge temperature' series in the second chart, no? That probe is still measuring the air...

I'd say the oscillations are due to poor controller tuning, as indicated by the stripy bar (red/blue, heat/cool) down the bottom, with the controller repeatedly acting back-and-forth (heat, cool, heat, cool...). The tuning seems much better in the second chart.

And may I guess that primary fermentation is occurring in the second chart? This is causing the beer temp to increase - which the cooling is struggling to keep on top of (or perhaps not active at all)? Once the temperature calms down (fermentation slows?) below setpoint, the heating appears to control the beer temperature very well.

3) Why is the beer temperature setpoint constantly rising in the second chart? Ramp rate on setpoint change, perhaps?

4) Are you able to vary the heating/cooling duties with the brewpi at all? Or is it just an on/off, bang-bang controller operation?

Cheers.


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## Glot (25/12/13)

There s a reasonable ( for the price) two channel thermometer for about $20 on Ebay. The thermocouples are about $2 each. If you want to do some measurements without going to the expense of a multi channel recording thermometer, just seal some sanitised sensors in the fermenters, fridge air, fridge glass of water, side of fermenter etc and plug them is to read them when you want. I usually run two fermenters at the same time. I have a sensor in each one just to use as a double check and to offset my temperature controller. It also makes a difference wether the fermenter is on the top shelf or bottom shelf but I just compromise and average them.
While active fermentation is occurring, there should be enough gas movement to reduce temperature stratification. If in doubt, just put one sensor high and one low.
I am just offering some cheaper alternatives to those keen to follow their temperatures more closely.


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## jkeske (2/1/14)

beermeupscotty said:


> *jkeske*, awesome data! Great reference for those looking at temperature measurement and considering getting a thermowell (i.e. me ).
> 
> I'm establishing a new setup with temp control, and looking at your data, seeing the dT between the two measuring points, I thought I might forego the thermowell for now and instead just measure the side of FV and add an offset to the beer temp setpoint. However, the dT seems to change depending on the steadiness of the wort temperature. As the wort temp settles, the dT decreases as the two temps equlibrate, as zarniwoop and manticle mentioned. As others are suggesting, looks like it's worthwhile just to do it right (accurately) and be done with it, so I think I will get a thermowell.
> 
> ...


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## BilBrewing (16/1/14)

This is an interesting topic!

My 2c is Bertus Brewery's temperature monitor link. 

http://www.bertusbrewery.com/p/temp-monitor.html

He tapes the probe to the side of the fermenter and logs the data of both fridge and ferment temps. Despite the big swings in fridge temps the wort stays fairly constant. Reading through his blog he usually begins his ferments slightly cooler and raises the temps later on. Whether this is to account for the wort (during primary) being a higher temp than the probe measures through the side of the fermenter i can't answer specifically. 

I use this same method. So far it works a-one, but i'd be interested, from a obsessive compulsive point of view, to understand how much the primary fermentation lifts the temperature above what my probe is measuring. 

After reading all these opinions i think i might try just running the probe right into the wort.


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## Spiesy (16/1/14)

verysupple said:


> Yeah, that should work fine because the probe and thermowell _should_ be in equilibriuim. The issue is if you're relying on air to transfer heat between the thermowell and probe.


The probe is touching the thermowell. Metal on metal. Very little to do with air.


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## hellbent (16/1/14)

Hmmmmm............... It wasn't that long ago I had wet towels and a fan trying to control my temps, just glad I hadn't read all about this scientific stuff then, woulda had to go and get 2 fans in case one was out by a few revs!


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