A Great Place To Shove Your Temperature Probe

[Darren]

Hey,

I would have thought that if your probe was in the wort you would also need to have the cooling mechanism in the wort too.

Putting your probe in the wort is stupid. It creates an additional infection risk but mainly, how long would the fridge have to be running to cool/warm the wort to the desired temp? Your fridge would get to 4 degrees fairly quickly if you needed to drop your wort tem (in the centre I presume) by 2 degrees. How do you off-set that cool fridge interior.

For a lager, I can see that in the wort may have its benefits. For an ale though, it is a waste of time. You are better off maintaining a constant fridge temp by placing the probe outside as it is all usually fermented in less than the time it takes to cool a few degrees.

cheers

Darren

 

[Ross]

Hey,

I would have thought that if your probe was in the wort you would also need to have the cooling mechanism in the wort too.

Putting your probe in the wort is stupid. It creates an additional infection risk but mainly, how long would the fridge have to be running to cool/warm the wort to the desired temp? Your fridge would get to 4 degrees fairly quickly if you needed to drop your wort tem (in the centre I presume) by 2 degrees. How do you off-set that cool fridge interior.

For a lager, I can see that in the wort may have its benefits. For an ale though, it is a waste of time. You are better off maintaining a constant fridge temp by placing the probe outside as it is all usually fermented in less than the time it takes to cool a few degrees.

cheers

Darren

I refuse to bite.... Do whatever floats your boat

cheers Ross

 

[BrissyBrew]

...I would have thought that if your probe was in the wort you would also need to have the cooling mechanism in the wort too....
...Putting your probe in the wort is stupid. It creates an additional infection risk
Darren

If air surrounds your fermenter you have 360 degrees coverage.

As far as infection goes, the probe is a single piece of stainless steel, a quick spray of idophor (or your fav. sanitising solution) before insertion that that's it, I think the additional risk is is minimal to say the least.

I should dig it up but somebody logged a brew with three data loggers, one outside the fridge, one inside air temp and one inside the wort. What I did remember is in early fermentation wort temperature was 8*C above the air temp.

 

[PostModern]

Think about a non-modified fridge. It's thermostat is in the airspace, not in your bottle of milk. Do normal fridges cycle too often?

I keep my fermentation probe in the airspace. I subscribe to the theory as discussed above, that the thermal mass of the wort will keep it within a degree of the set temperature most of the time. A probe in wort would have to be set with <1 degree of variance.

Here's the scenarios:
a) Probe in wort.(or taped to side of fermenter) Temp set to 17 with 2 degrees variation (ie compressor cuts in when temp is 19 and out when 15). This means your wort will slowly vary between 20 and about 14, because the coolness of the fridge will keep chilling the wort even when the compressor has cut out, and when it cuts in, the temp will keep rising at least a degree before it starts dropping. Moreso with early fermentation.


b ) Probe in air space Temp set to 16 with 2 degrees variation. The wort will reach about 19 before the probe reads 18 and kicks in the compressor. The compressor will then chill the air space to 14 before cutting out. The thermal mass of the wort will prevent it dropping this cool, maybe 16 before it stabilises with the air temperature then the exothermic behaviour of the fermentation will start the cycle again.

I like b best. I set the temp to two degrees cooler than I want the fermentation to be. With the probe in the wort, you have to shift the temperature of the whole mass of the wort. The compressor will run for longer, and the variation in the wort's temperature will be greater. If you set the variation to be one degree instead of 2 or three, the compressor will cycle more often, creating the exact problem you sought to avoid.

I'm not religious about this, tho. If someone could convince me of the merits of attaching the probe to the wort (or using an internal sensor), I'd change what I do, but I think my theory is sound.

 

[bindi]

I should dig it up but somebody logged a brew with three data loggers, one outside the fridge, one inside air temp and one inside the wort. What I did remember is in early fermentation wort temperature was 8*C above the air temp.

I placed 2 probes with the new brew, one taped on the outside and one in the wort, and after 12 hours there was a 5c gap still.

 

[newguy]

I don't think there's a completely foolproof (i.e. 'correct') method of tightly controlling the temperature of fermenting beer no matter whether the probe actually contacts the beer or just the air in the fridge/freezer.

I designed and built my own HERMS (heat exchanging recirculating mashing system) and I can tell you from experience that a simple thermostatic (on/off) control action leads to overshoot/ringing of the temperature of the mash, and I'm very skeptical that beer in a fridge would be any different. The problem with thermostatic control is that it ignores the rate of change of temperature. An analogy would be driving your car to a cliff without going over it: if your approach speed is slow, chances are that simply taking your foot off the gas will allow the car to stop before it gets to the edge. Conversely, if you approach the cliff at 100 km/h, you'd have to take your foot off the gas much sooner to avoid catastrophe. What about brakes? In the thermal system of a refrigerator and the beer, there are no brakes. In this example, brakes = heater, gas pedal = cooling system.

I grossly underestimated the thermal mass/thermal momentum issue when I first put together my system and implemented a very simple modified thermostatic control algorithm. When I tested it, the system was so unstable as to be completely useless. I had to implement a much more complex PID (proportional-integral-derivative) control algorithm. PID control, in and of itself, isn't that hard to implement. The real bugger is tuning the system so that it displays optimal (i.e. no overshoot) temperature control.

The real issue is varying the cooling/heating 'power' as required. With an electric heating element, this is easily achieved by cycling the power to vary the 'on' time in relation to the 'off' time. With a fridge/freezer, good luck. It's either on or off, not in between.

Although I'm not a pro brewer, I know a few and have toured their breweries. I can assure you that their temperature control of most of their fermenters is analogous to the probe measuring the air temperature inside the fridge, not measuring the temperature of the beer. With ales anyway. The fermentation room is usually kept at a preset temperature, and they usually don't measure the temperature of the beer. Just like a giant fridge. If they ferment lagers in the same fermentation room as their ales, that fermenter will likely have a glycol jacket cooling system.

 

[Screwtop]

Time to set the cat among the pidgeons.

What about the location of the probe in the wort, and stratification. Does fermentation activity (CO2 production) move the wort around or do the bubbles move freely without disturbing the equilibrium of temperature stratification in the wort. Would naturally occuring layers in wort be difused by CO2 bubbles transversing such a layer. Would thermal convection play a part, would inversion layers or capping inversion layers occur, maintaining temperature stratification. Would CO2 bubbles travel more slowly through the more dense lower temperature layers and faster through the warmer layers. Air in the fridge is going to be cooler at the bottom of the cabinet than at the top, temperature of the air effects the temperature of the fermenter and the temperature of the fermenter effects the temperature of the wort, and vice versa. There is an equal and opposite reaction occuring continuously at the interface of each element and within the mass of each element, parts of the fermenter mass will be at different temperatures, but will be attempting to reach equilibrium. The air (inside and outside the fridge cabinet), fermenter material and wort, will all be effecting each other, how can such a system ever reach equilibrium when the one and only element we have control of (inside fridge air temp) is being controlled by an astable system (refrigeration system), simply incapable of maintaining a static temperature setting. In an attempt to reach equilibrium each element will affect the other, this effect occurs in both directions as physics dictates.

I have put all of this stuff in the IBU (interesting but useless) category and simply use a probe in the airspace. No matter what measures are taken, wort temp will fluctuate and vary at differing points throughout the wort. Is it more important to measure the wort temp at the bottom (for bottom fermenting yeasts)? or the top (top fermenting yeasts)? or should the average of temps taken in varying locations in the wort be used?

I'M SO CONFUSED, think I'll have another beer and see if I can reach equilibrium :chug: ,would only make a poofteenth of a difference anyway.

 

[warrenlw63]

:lol: :lol: What a thread this one's turning into.

Anybody would think some of you blokes are fermenting hectolitres rather than 23 litres. :blink:

I just stick my probe between the two fermenters with some convoluted foam. Beer tastes fine. Question you've got to ask yourselves collectively is this... Is there a problem with the finished beer in terms of bad fermentation byproducts? If not then what difference does it make where your probe is, so long as some basic stable temp control occurs it's all good. :beerbang:

Edit: For the anal among us perhaps a rectal probe is in order?

Warren -

 

[Wortgames]

Does measuring the temperature change it?

The application of quantum thermodynamics in fermentation, love it :beer:

Regarding the stratification - a fermenting wort heaves and rolls like you wouldn't believe, apparently it depends more on fermenter geometry than anything else. I doubt stratification would be an issue at all, especially in the volumes we are dealing with.

If you've got the technology and you can be bothered, then a probe in the wort with a suitably accurate controller is probably a slightly better way to do it, although the more 'thermal mass' you have between the chilling or heating mechanism and the probe (ie the fridge + the air + the fermenter + thermal gain due to insulation inefficiency + the wort) the slower the cycling and the greater the amount of overshoot. With a 2-stage controller this could lead to the heating and cooling systems actually fighting each other.

Personally I monitor the air temp in a commercial (fan-assisted) fridge, it just seems easiest and I believe it does the trick. In the future (if and when my fermenters are stainless) I may attach a probe to the outside of the fermenter, but I don't think I'd bother immersing a probe - I just don't really see it making enough of a difference to justify the inconvenience (small though it may be) of having something else to clean and sanitise and connect up and get in the way etc etc etc.

 

[jupiter]

i have two thermocouples in my fridge space, 1 measuring inside air temperature, the other is taped to the side of the fermenter with a 1cm2 piece of adhesive copper tape with a 4cm2 piece of adhesive aluminium tape over the top and a big strip of gaffer tape over the top to strap it all on and support the thermocouple wire.

my temperature controller uses the taped thermocouple to control the compressor. i found using the air temperature thermocouple to control temperature, the compressor cycled on and off frequently and the fermenter temperature was dependent on the rate of fermentation and the fermenter sat at an approximate average 3degC above the inside fridge air temperature.

i was initially considering sticking a probe into the wort, but that quickly landed in the too hard basket (too much effort for little return).

 

[SpillsMostOfIt]

I think this thread is becoming a bit like some of the sanitation threads that have come and gone. My only (current) question on both issues remains 'How did they get by 300 years ago?'. (Apart from the issue of having to walk tens or hundreds of miles to find other brewers to argue with.) Either they ditched a lot of beer or they had something right that we, collectively (or is it just me), are missing?

 

[bindi]

I think this thread is becoming a bit like some of the sanitation threads that have come and gone. My only (current) question on both issues remains 'How did they get by 300 years ago?'. (Apart from the issue of having to walk tens or hundreds of miles to find other brewers to argue with.) Either they ditched a lot of beer or they had something right that we, collectively (or is it just me), are missing?

They only brewed during the right season and unlike us did not try and brew a Lager in Queensland during summer, or for that matter most Ales.
Like trying to grow rice and cotton [Cubby Station and others] in a dry land <_< wait a sec, the silly pr$cks a doing just that . h34r:

 

[Ross]

I think this thread is becoming a bit like some of the sanitation threads that have come and gone. My only (current) question on both issues remains 'How did they get by 300 years ago?'. (Apart from the issue of having to walk tens or hundreds of miles to find other brewers to argue with.) Either they ditched a lot of beer or they had something right that we, collectively (or is it just me), are missing?

Even far less than 300 years ago - The 1st brews in Australia were all brewed without fermentation control, & pretty disgusting they were too by all accounts.
++
The forum is for discusing opinions, facts & ideas, without discussion the forum would be boring. A thread like this can be of interest to quite a few, with new ideas learnt. From what I've read above, many seem happy with measuring air & are no doubt happy with their results, & as some have mentioned, a small difference in temp will probably not make much difference anyway. Others like myself who have actually measured the difference, have seen it can vary more than we are happy with & hence we prefer to measure the wort either by probe or stuck to the fermenter. If the threads of interest, you read & make your own judgement - If it's of no interest, then simple to ignore.

Cheers Ross

 

[SpillsMostOfIt]

The 1st brews in Australia were all brewed without fermentation control, & pretty disgusting they were too by all accounts.

Were they CUB products?

 

[Wortgames]

Brewers of old used to throw away A LOT of beer. Before they began to figure out yeast in the eighteen-wotsits it was all voodoo and luck.

In fact, the Pilsner Urquell brewery was created as a community facility when all of the local breweries had to dump barrels full of undrinkable beer leaving the villagers with no grog.

 

[Screwtop]

Brewers of old used to throw away A LOT of beer. Before they began to figure out yeast in the eighteen-wotsits it was all voodoo and luck.

In fact, the Pilsner Urquell brewery was created as a community facility when all of the local breweries had to dump barrels full of undrinkable beer leaving the villagers with no grog.

Lot to be said for a modified practice of old "making a starter". If the beer (starter) is good then go for it and make more wort to add. Was only the small infected (proof) batches that were thrown out.

 

[BrissyBrew]

Here's the scenarios:
a) Probe in wort.(or taped to side of fermenter) Temp set to 17 with 2 degrees variation (ie compressor cuts in when temp is 19 and out when 15). This means your wort will slowly vary between 20 and about 14, because the coolness of the fridge will keep chilling the wort even when the compressor has cut out, and when it cuts in, the temp will keep rising at least a degree before it starts dropping. Moreso with early fermentation.
b ) Probe in air space Temp set to 16 with 2 degrees variation. The wort will reach about 19 before the probe reads 18 and kicks in the compressor. The compressor will then chill the air space to 14 before cutting out. The thermal mass of the wort will prevent it dropping this cool, maybe 16 before it stabilises with the air temperature then the exothermic behaviour of the fermentation will start the cycle again.

I'm not religious about this, tho. If someone could convince me of the merits of attaching the probe to the wort (or using an internal sensor), I'd change what I do, but I think my theory is sound.

SCENARIO A
Probe Inserted in Wort.

Small fan to circulate air inside the fridge/freezer unit.
Set temp 17*C
Unit will turn the compressor on when the wort hits 19*C
Unit will turn the compressor off when the wort hits 16*C

The air temperature of the fridge responds quickly if a fan is inside the unit, so when it kicks in the cooling effect will be reasonably immediate. With a fan running in the unit you are also adding a little bit of heat to the equation but probably not enough to make any difference. However you are correct you can overshot the target temperature especially early in fermentation, eg the compressor turns off at 16*C and the cool air in the fridge keeps chilling, the over shoot will depend on a number of factors, is any heat being generated from the wort, thermal conductivity of your fermenter, volume of wort vs cooling capacity of the air inside the fridge. The over shoot, or under shoot of temperature is the biggest concern, especially if you are dropping the temperature of wort that started at say 24*C, best monitored for the first couple hours.

SCENARIO B
Probe Inserted in airspace.

Small fan to circulate air inside the fridge/freezer unit.
Set temp 17*C
Unit will turn the compressor on when the air temperature hits 19*C
Unit will turn the compressor off when the air temperature hits 16*C

The air temperature responds rapidly with a fan inside your unit (you can stand their and watch it drop), however just because the air temperature arrives at the target temperature does not mean your wort has. If you pitched a little warm, your fermenter could still be at the original temps, as I stated it does not take long for the air temperature to adjust. If the fermentation is producing heat, you will need to wait until the heat produced is sufficient to warm the air, to enable the compressor to turn on. The system will settle and move towards equilibrium, eventually. However it is early fermentation that plays a key role in fermentation flavour by-products.

In short Scenario A is better for early fermentation IMHO (people are free to sick there probes wherever they like). And Scenario B is better for long term lagering. After crash chilling I simply insert the probe for early fermentation and pull it up a bit and leave it in the airspace inside the fermenter (probably middle grounds between scenario a and B) for lagering.

In the early stages I want to know and measure the fermentation of my wort, not the air temps of my fridge which after awhile and all the action is over will reach equilibrium the wort.

 

[Tony]

OK i thin ki know where PP is comming from here.

He is concerned with how the controller is going to crash chill the wort but then steady out to hold temperature when required.

most get confused with the whole concept of a thermostat and the temp controller controlling the fridge.

My set up has the probe in the wort, as u can see from the pics in the first page i think.

The probe is hooked up to a temperature controller that will control to within 0.1 deg c.

I have a 0-40 deg thermostat but it stays on 2 to 4 deg no mater what. It isnt the thermostat that is controlling the brews temp............ its the temp controller.

The trmp controller is hooked up to a power point that switches the power on and off the the fridge............ yes the fridges power lead plugs into my temperature controller.

If i put a 60 liter firmenter in with 50 literd of 30 deg c wory and want it at 20 deg to pitch, i set the fridges thermostat at 2 deg. this way the fridge will cool down to its coldest setting without freezing and cut out like its suposed to.

the temp controller will keep power on the fridge untill the beer is at 20 deg and them turn off the power when it reaches temp. the thermostat has cut in and out as it should to keep the fridge at its coolest temp to drop the wort temp quickly but hasnt run continuously and burnt it out.

it will them just cycle power every now and then to keep the wort at a steady say 19 deg. the fridge gets down to about 16 i think.

It works fine and doesnt over work anything.

Another thing is i have the end of my fridge thermostat in a 600ml bottle of metho to measure liquid temp and not air temp. It buffers it and snoothes out the fridges cycles

Its full of metho cause metho wont runt the metal and will never go mouldy. I just drilled a hole in the bottles lid and then sealed it with silicon

Its been like that for over 3 years

cheers

edit......... i was going to fix the spelling but there are some great ones in there so i left it

cheers agian

 

[browndog]

I'd like to stick my bib in here and for all the dummies (of which I am one) can tell you all the techinical discussion here is all about lag between your set point and actual temps. If the probe is in the fermenter and it says the temp at the center of the fermenter (or where ever the probe is) is at 18C then at the outer edges of the fermenter it is going to be colder when the controller tells the fridge to shut down. And the exact opposite for having the probe in the airspace. If you can imagine your ideal wort temp as a nice straight line then the actual temp will occillate above and below this in waves. We want our waves (and hence our lag) to be as shallow as possible. As the wort has a huge thermal mass compared to the airspace in the fridge, it will tend to occillate less giving a more stable temperature control IMHO. I'm no scientist, but have done quite a bit of proccess temperature control though my work. I happen to have a Data Logger with 12 inputs and am prepared to do an experiment to see how the temperatures work within the fridge and the wort. We should be able to sort this out and see exactly what goes on. I'd like to hear some ideas of where to place the thermocouples.

cheers

Browndog

 

[PistolPatch]

Tony: I want your gear My problem is that my fridge probe no longer works so I just have Frank's controller. Being a freezer, if I have the probe in the wort the freezer is going to run continuously and drop to at least minus 25 until the wort hits 18. Having it in the airspace inside the fermenter above the wort seemed to solve the crash chilling part really well which brings me to...

Browndog: You are the man. That'd be a great experiment. I'd be really interested to see how differently a probe taped to the side of the fermenter worked compared to it being in the airspace in the fermenter. I'm guessing that they would act similiarly but it would be great to know for sure. Look forward to hearing the results.

I'm with you Warren on the lol's