Temp question

[j4c]

Hello.
My brew is in a freezer that I haven't converted yet.
The temp in there is 18.5c
Is it the temp of the freezer space I need to keep an eye on or the fermenter itself.
I can tape my probe to the side of the bucket.


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[Troutman47]

Temp of the fermenter.

Although the temp of the wort will rise a bit when the yeast kicks off.
All that sexy budding action!
Ya'know what I mean!

[Rogermort]

Put the probe in a jar full of Starsan. Monitor the temperature of the liquid.


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[j4c]

Oh OK.
So I'm not trying to cool the fermenter when the yeast warms it just keep a constant in the freezer.
Thanks

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[rpt]

There are a variety of opinions on the best way to do this. I tape the probe to the side of the FV and cover it with bubble wrap.

Sorry to disappoint you, but by definition there is nothing sexy about budding.

[TheSumOfAllBeers]

The temperature of the fermenter is the important thing

[BrannigansLove]

Put the probe in a jar full of Starsan. Monitor the temperature of the liquid.


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I disagree, starsan doesn't generate heat as the beer will during fermentation. I attach the probe to the side of the FV using plumbers clay.

[j4c]

The probe is on the side of the FV. I have put a strap around it to hold it. Is like neoprene.
The temp has crept up today from 19.4 to 20
It's bubbling away.
I have a temp controller but the heater isn't ready.
Will it be OK to set it to 19c with just the freezer working or will it just push it to low as it stays cold inside after the freezer cuts out.


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[rpt]

Yes, that should be fine. The wort has a much greater thermal mass than the air around it.

[TheSumOfAllBeers]

The freezer itself is a great insulator from ambient temp swings too

[Kev888]

There will always be differences in opinion, because freezers (and fridges) are thermally coupled to the fermenter by air. This is not a very good conductor and so allows appreciable difference/separation between what the freezer is doing, what effect that has on the air, and what effects are felt by the wort. There are (IMO) two main features of this system:

Firstly, measuring the temperature of the wort will be more accurate, partly since it also detects the effect of the fermentation heating itself. However the wort has a large thermal mass which changes temperature only slowly, and so measuring the wort yet controlling the freezer compressor (especially if you bypass the thermostat) can allow the latter to be on constantly for hours, even days, at a time. Which it isn't really designed to do and which can cause over-heating (I had this). Conversely, measuring the air is kinder to the freezer but is less accurate for the wort temperature, especially during peak activity when it heats itself.

Measuring the wort and not bypassing the freezer's thermostat is my preferred approach, since the in-built thermostat will pause the compressor and give it at least some rest each time the air temperature drops sufficiently. Its not as necessary to bypass freezer thermostats as it is for fridges; freezer stats offer more leeway for crash cooling without as much interference; when they do interfere it is briefly and helps protect against overheating. Compromising is another option: putting the sensor against the fermenter so that it has some recognition of both wort and air temperature can work quite well, or using a smaller jar of liquid that is affected by air but not as immediately as being in the air itself can also help, though it knows less about what the wort is doing.

The second issue is the resolution of the thermostat (the actual/control resolution, not the display resolution). if your thermostat has a high resolution, say +/- 0.1c, then measuring the wort is a reasonable approach. If it only has low resolution, say +/-1c (so 2c) or worse, then that is quite a large swing - putting the sensor in the air can cause a more consistent wort temperature, since the wort (with its large thermal mass) only changes a tiny bit and so averages out the bigger controlled swings in air temperature. However, you have to manually adjust to compensate for self-heating during the vigorous stages of fermentation.

Some thermostats also allow an adjustable 'dead band' which can be used both to stop cooling and heating chasing each other; which is more likely when measuring the more responsive air and/or when using finer resolution controller. All thermostats used to control the compressor should have a time delay, so that the compressor can't be cycled on/off too rapidly whatever happens.

[j4c]

Thanks guys
I put the heater in last night.
The thermostat is set at 0.3c for the swing each way.
Seems to be stable.
Kev that post was epic. Has made me happy with my decisions.
Cheers

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