Beer fridge, sensor on FV or in free air?

[Nial]

The wife was working this weekend, I managed to get a second hand larder fridge on Gumtree for £30, cleaned and
installed in the garage without her noticing!

I have an ITC-1000 controller on the way. What's the consensus for mounting the sensor, insulated and
against the FV, or mounted in free air somewhere safe?

Thanks for any pointers,

Nial.

 

[HisDudeness]

I go for the side of FV with foam over the top, the fermentation generates its own heat so ambient air temp does not always correlate with wort temp. This way is more likely to maintain stable fermenting temp which is key for good yeast performance

 

[MickDundee]

I have the Inkbird with the 12" sensor and I have this suspended in my FV, has been pretty steady between 18 and 19C. I don't have a brew fridge though, just a cupboard.

 

[TheRedDarren]

I don't have the 12" sensor so I go with what The Dude said, tape it to your fv with a wodge of foam.
In free air you'll have a huge yoyo effect as air is no where near as stable as fluid when it comes to holding temperature.

 

[Bigcol49]

Hi!
+1 for for HisDudeness.

 

[houndeye]

hi.i've got mine against fv and its about 1c difference to the temp of the wort

 

[Spoon]

I don't have the 12" sensor so I go with what The Dude said, tape it to your fv with a wodge of foam.
In free air you'll have a huge yoyo effect as air is no where near as stable as fluid when it comes to holding temperature.

Which is why it SHOULD be in the air. You want the sensor to yo-yo, not the beer. Remember the sensor is always going to go +/- whatever you set it, would you rather it was taking the beer with it?

Say it's set at 19 +/-1. Taped to the side the FV drops to 18, warms upto 20, drops to 18 etc. In the air the air drops to 18 (but the FV is still 18.9), rises to 20 (but the FV is probably 19.1). The downside of that is that the heater and compressor will cycle more often (but will be on for less time, so it probably balances out).

Fermentation kicks off some heat, but unless the bucket is particularly thick, or insulated it's probably less of a temperature change than the accuracy of the controller.

Where I deviate from that principle is in the first 24h and when cold crashing. Because in the first 24h I want to get the beer from whatever temp I pitched the yeast at to the fermentation temp ASAP, and ditto during cold crashing I want it as cold as possible (arguably better to bypass the STC and plug the fridge back in). Hanging in the airspace will get there eventually, but it takes a bit longer.

 

[Brew_DD2]

That's a very interesting point Spoon and one I'd never considered before. It's seemingly the consensus that people tape it to the side of the fermenter, but to my mind your post made a lot of sense.

 

[TheRedDarren]

Which is why it SHOULD be in the air. You want the sensor to yo-yo, not the beer. Remember the sensor is always going to go +/- whatever you set it, would you rather it was taking the beer with it?

Say it's set at 19 +/-1. Taped to the side the FV drops to 18, warms upto 20, drops to 18 etc. In the air the air drops to 18 (but the FV is still 18.9), rises to 20 (but the FV is probably 19.1). The downside of that is that the heater and compressor will cycle more often (but will be on for less time, so it probably balances out).

Fermentation kicks off some heat, but unless the bucket is particularly thick, or insulated it's probably less of a temperature change than the accuracy of the controller.

Where I deviate from that principle is in the first 24h and when cold crashing. Because in the first 24h I want to get the beer from whatever temp I pitched the yeast at to the fermentation temp ASAP, and ditto during cold crashing I want it as cold as possible (arguably better to bypass the STC and plug the fridge back in). Hanging in the airspace will get there eventually, but it takes a bit longer.

I've got to disagree, sorry fella.
Taping the sensor to the fv has always resulted in no more than 1 degree of difference between the wort and the reading on the stc, and when cold crashing it gets it down within 24 hrs.
I've tried it in free air and it cycles like crazy and the sensor doesn't correlate with the temp inside the fv when tested with another thermometer.
It may be the difference between theory and practice.

 

[HisDudeness]

I must also respectfully disagree. Because it takes a lot of heat/cooling for the wort to change temp you actually want the air temp to overshoot the target up or down or it will take a lot longer for the liquid temp to change. The heater/fridge will raise or drop air temp very quickly and cut out the controller before the wort temp has even moved if it is measuring ambient air.

The Brewing Elements book on Yeast is fairly clear on this point when discussing fermentation temperature control:
"In all these methods, it is critical that you measure the temperature of the beer. You want to control the beer temperature, not the air temperature."

 

[duncans]

Yep, measure as close as possible to liquid temp. That's what you are trying to control in fermentation fridge.

 

[Inkbird]

Hi all, I know that there's temperature difference between in the FV and the ambient temp. As MickDundee said, it's good to have inkbird 12"/30cm long sensor, this is IP68 waterproof, you can put in your beer directly with a casing.

 

[Leon103]

I out mine on the wall off the fridge. Fan circulating air. No issues so far

 

[Nial]

Thanks for the feedback guys.

When things are up to temperature there's probably not much difference, but when you're heating or cooling having it on (or in) the FV is probably
better?

I've got some 50mm Kingspan insulation, I'll shape this to fit the side of the
FV and get a big bit of elastic!


Nial.

 

[BreadMurderer]

I've always taped it to the FV thinking that the closer to the beer it is the better, as the beer temperature is more important than the air temperature. My thoughts anyway.

 

[Twostage]

Posts #13 and #18 :-

http://www.thehomebrewforum.co.uk/showthread.php?t=54503&highlight=temperature&page=2

Read #18 first.

Post #18 demonstrates how using the probe in/attached to the FV creates a cycle of cooling/heating/cooling/heating as the liquid lags behind chamber temp and the liquid ends up varying in temp by 1.5c Whereas with the probe in the air the liquid settles to the air temp and varies by less than .1 degree. This experiment was with a non-fermenting liquid to demonstrate the principle.

Post #13 is a real life fermentation controlled with the probe in the air. The brew generates its own heat but only about 1.5c at its peak and it is actually useful to monitor its temperature as you can track progress better than just watching the airlock, particularly the later stages when there is activity that doesn't generate CO2.

Obviously monitoring the brew directly works but you are wasting energy and actually controlling it less than air temp control.

By the way, if you are using the probe attached to the FV method it is worth doing a 'leave the fridge door open for a few minutes' test. If you start to see a drop in temp from your probe it isn't insulated enough and you are actually monitoring air temp.

 

[Spoon]

[edit, typed too slowly, I agree with Twostage, the flowing is aimed at those monitoring FV temp]

But when you put milk (or beer for that matter) in the fridge, do you ever worry that when you take it out it won't be at the fridge temperature?

It comes down to which do you think is better/worse. Cycling +/- the dead band. Or the FV sitting 0.5C above the set point due to the heat it generates.

But in all seriousness, do you really know what fermentation temp you want to within 0.5C? and as an extension to that, does it therefore matter?

 

[Bigcol49]

Hi!
The conclusions here are interesting: http://www.jimsbeerkit.co.uk/forum/viewtopic.php?f=6&t=68518
It's from another place.
May I add that, when it comes to sensor placement, one is either Catholic or Protestant, and no amount of data or reasoning is going to make any difference.

 

[Twostage]

Hi!
The conclusions here are interesting: http://www.jimsbeerkit.co.uk/forum/viewtopic.php?f=6&t=68518
It's from another place.
May I add that, when it comes to sensor placement, one is either Catholic or Protestant, and no amount of data or reasoning is going to make any difference.

Yep, seen that thread and must admit have been tempted to sign up and do a review of it but its and old post and the poster doesn't seem to be posting any more so it seemed somehow not fair. Maybe I should reconsider if it is still being referred to.

The fact is they have made a fundamental error.

Why is it flawed ? In experiment 4 (the one that they promote as being the best option) they say they put the probe on the FV and therefore it is the beer temp that is controlling the heating cooling cycle. But the sensitivity of the STC is .3 degrees so the thing that is being monitored must vary by at least that to make it switch. In the experiment the beer only changes by .19 degrees, therefore it is impossible that the beer is controlling the STC, .19 degrees isn't enough to make it switch. It should really have stood out for them that something was wrong. They repeat the mistake in experiment 7.

Now compare experiment 5 (probe in the air) with experiment 4 and ignore the beer temp you can see that the variations in chamber temp are exactly the same pattern. The ONLY different between them is the starting temperature of the beer. Experiment 4 it starts at the right temp, experiment 5 it starts low and has to warm up. In other words they are the same experiment but with a slightly different starting temp of the beer. If you look at the last quarter of the graph in each case they are identical.

My conclusion is that either they didn't insulate the probe and simply stuck it to the side therefore it was actually monitoring air temp or they simply set it up wrong somehow.

Personally I don't see it as a belief thing and I think there are many that genuinely want to understand what happens and what the differences are so they can make an informed choice.

Both make beer though :-)

 

[Robbo100]

Well, rather than use an "off the shelf" solution for regulating FV temperature, I personally use a Raspberry Pi powered system.

With this, I measure both air temp and fluid temp (with the sensor on the outside of the FV with a lot of insulation covering it).

I get about 2 deg per hour change of the wort during cooling or heating periods (based upon a 30 ltr batch) and once at the desired temperature, the wort stays within +/- 0.12 degs for the duration of the fermentation.

So, my answer is that to do it properly, you need to measure both!