Temp sensor positioning during crash chill

[sbond10]

Just wondered where you all keep your temp probes when crash chilling. During active ferment I have mine taped to the side of fv under bubble wrap and keep here during chilling but it does take ages to go ferment temps to below 5 c (rounghly 12 hours +). Now reading through various lager method s it actively suggests to remove the probe after active ferment and let it monitor free air rather than being taped under.
So I'm just wondering if during crash chill it matters as much the main reasons are.
1) the length of time it takes to drop to crash chill temps is this healthy for the fridge motor to be running for 12 hours
2) the energy costs associated with this constant running.
3) more stable temps monitoring free air

Any advice thanks in advance
Sean

[AnthonyUK]

Measuring the FV temp will be the quickest to get to the required temp. All you'll be doing by measuring the air would be extending this time due to the poor conduction properties of air.

Costs will be minimal in the range of a few pence per day and will not be a problem for a modern fridge.

[f00b4r]

Also, unless you have bypassed the thermostat wiring, you are at most just running the fridge as if it's on its coldest setting prior to adding the STC/Inkbird device.

[Mr Squiffy]

Many people will disagree with this but MEASURE THE AIR, do not stick it to the side of the FV unless you have a second probe in the air that prevents overshoot. The bulk of the wort will settle at the air temperature. Sticking it to the FV with a single probe will unnecessarily overwork the fridge and may cool the wort lower than intended (if your fridge is good enough that is).

[AnthonyUK]

Many people will disagree with this but MEASURE THE AIR, do not stick it to the side of the FV unless you have a second probe in the air that prevents overshoot. The bulk of the wort will settle at the air temperature. Sticking it to the FV with a single probe will unnecessarily overwork the fridge and may cool the wort lower than intended (if your fridge is good enough that is).

That would ever happen. The cooling capacity of the air in the fridge is not enough to continue cooling 20 odd litres of liquid that much.
Of course both will work as the air and the FV will eventually equalise temps but air is just not a good conductor.

[MTW]

Many people will disagree with this but MEASURE THE AIR, do not stick it to the side of the FV unless you have a second probe in the air that prevents overshoot. The bulk of the wort will settle at the air temperature. Sticking it to the FV with a single probe will unnecessarily overwork the fridge and may cool the wort lower than intended (if your fridge is good enough that is).

Very interesting thought. I am a BIG advocate of the bubble-wrapped-probe-on-FV method for the fermentation (in the absence of a multi-probe setup) and I know it keeps the central wort temperature very close indeed to what I've set, over many brews. However, that's a very good point about placement during a hard chill, long after the yeast has stopped producing any of its own heat, and I can see why it would avoid the fridge working harder than necessary.

You've probably just elicited a nice little tweak to my longstanding method there Mr Squiffy!

[Only small downside is that I will now have to test the wort directly with a thermometer if I want to record the point at which it gets down to the desired chilled temperature.]

Many people will disagree with this but MEASURE THE AIR, do not stick it to the side of the FV unless you have a second probe in the air that prevents overshoot. The bulk of the wort will settle at the air temperature. Sticking it to the FV with a single probe will unnecessarily overwork the fridge and may cool the wort lower than intended (if your fridge is good enough that is).

That would ever happen. The cooling capacity of the air in the fridge is not enough to continue cooling 20 odd litres of liquid.

I was reading Squiffy's 'overshoot' as meaning the air temperature in the fridge would overshoot (downwards) at points because the probe is getting warmth from the FV if it's taped to the side during the chill. ie, you set your STC to 5C, probe on the FV, but at points, the fridge will chill the air to (say) 2C (if it can). If the beer is currently 18C, then that extra -3C will hardly make any difference to how quickly it gets down to the intended 5C; the 'air overshoot' will speed things a bit once the beer is down to 6 or 7C, but in the meantime, you've worked your fridge harder than required.

[vacant]

Worth a read

viewtopic.php?t=68518

[Mr Squiffy]

Many people will disagree with this but MEASURE THE AIR, do not stick it to the side of the FV unless you have a second probe in the air that prevents overshoot. The bulk of the wort will settle at the air temperature. Sticking it to the FV with a single probe will unnecessarily overwork the fridge and may cool the wort lower than intended (if your fridge is good enough that is).

Of course both will work as the air and the FV will eventually equalise temps but air is just not a good conductor.

True, air is not a good conductor but fridges work by air conduction.

[AnthonyUK]

True, air is not a good conductor but fridges work by air conduction.

They are also not designed for fermenting beer or cooling large thermal masses which is why we need to use other methods more suitable for our requirements

Cooling is not so critical though and you are not looking for accurate temperatures just cooling beyond a certain point. I have a 6ft larder fridge and the biggest difference for me was fitting fans for when heating/cooling is active which assists thermal transfer.

[Jocky]

Worth a read

viewtopic.php?t=68518

Indeed, it is.

Personally I attach to the fermenter for the first 3-4 days of fermentation covered in a piece of thick neoprene, and then let the probe hang free in the fridge space after that.

But then I also allow for a 1c variation in temperature, and generally I only either need heating or cooling at any particular time - cooling in the summer and heating in the winter. It minimises the stress on the fridge.

When attached to the fermenter I've always found the reading settles to within 0.5c of the beer temperature.

[Fil]

pulling down to 5c within 12 hours isnt bad performance from your fridge at all imho, my own brewfridge has its internal thermostat bypassed and i can chill below 0C if requiered however it still takes the best part of 24 hours to achieve such a low temp especially if a diactyl rest is employed.

an internal fan will improve both chilling and heating efficiency as its the air inside the fridge which is the medium of heat exchange.

[sbond10]

Well it's floating free at the mo.seems a lot calmer and less coming on and off we shall see