Measuring Fermentation Temperature

[beerkravin]

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

 

[TSMill]

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.

 

[zarniwoop]

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

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.

 

[Kingy]

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.

 

[beermeupscotty]

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.

 

[Glot]

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.

 

[jkeske]

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)?

Yes, I have multiple probes to measure the beer temperature and the fridge temp at the same time. You can basically add as many probes to the brewpi as you want. I just bought a couple of new temp probes. Next brew I do I will tape one to the side of the fermenter and put a second one in the thermowell to measure the difference in a single brew.

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)?

The graph with the oscillations just shows that the temp probe taped to the side of the fermenter is being affected by both the wort and the air temperature. The oscillation in the beer temp graph are right in phase with the air temp. 20 L of wort is a pretty big thermal mass and there is no way it is going to oscillate that fast.


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...

Sorry I didn't really explain it, but in the second graph the fridge is turned off and the beer was left to free rise in temperature. So the set temp (red line) had no affect as long as the beer temperature was above it. you can see right at the end of that run the heater kicked to raise the fridge temp and keep the beer at the set point.

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?

The brewpi is completely programmable. You have total control over the fermentation temperature. you can set it to ramp up and down to your hearts content.

Cheers.

 

[BilBrewing]

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.

 

[Spiesy]

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.

 

[hellbent]

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!