A Rather Pedantic Question...

[joshesmusica]

I've read on here multiple times that people use bubble wrap around the temp probe taped to the side of the fermenter in the fermentation chamber. I've just been using either a small towel or a wool sock or something of the sort. But my wife came home with some bubble wrap, and I just had to make sure she didn't throw it away, because, I said, "Everyone on here suggests it." Then, she said, "But isn't air a poor insulator?" Which I thought about, and was in agreement about.

So what is better as far as insulating the probe from the actual air temp in the ferment chamber, and why? Bubble wrap, or a small towel, folded 2-3 times?

 

[BrotherBock]

I've tested the temp between a thermowell, electrical taped to the side of a carboy and the thermometer sticker. All gave the same temperature reading (give or take .5 degree).

Just tape it to the side and you'll have an accurate reading.

 

[TheHopfather]

I don't know the answer to your question. I use a small piece of sponge I cut from a larger one and it seems to work just fine. I cool my wort to pitching temps, pitch my yeast and move everything to my fermentation chamber. When I attach the temp probe and my sponge the probe always reads whatever my pitching temp was so I figure it is working fine.

If I had to guess I would think the towel would be better than the bubble wrap.

 

[CGish]

The idea behind the bubble wrap is that the air is trapped between two layers of plastic. While air alone is a poor insulator and plastic has limitations, together they form a decent level of insulation. (think multiple layers of clothes in the winter, or the old style house windows that trapped air between two panes).

Having said that, I can tell you from personal experience that a thermowell is worth the expense. My brewpi controller temp swings are wider and quicker with a probe taped to the outside of the fermentor than they are with a thermowell.

If you use bubble wrap, just layer it as much as you can.

 

[GilaMinumBeer]

Air is actually a good insulator because it has low density. The materials used in insulation are chosen more for the properties in creating interstices, or small pockets of air.

 

[passedpawn]

I've read on here multiple times that people use bubble wrap around the temp probe taped to the side of the fermenter in the fermentation chamber. I've just been using either a small towel or a wool sock or something of the sort. But my wife came home with some bubble wrap, and I just had to make sure she didn't throw it away, because, I said, "Everyone on here suggests it." Then, she said, "But isn't air a poor insulator?" Which I thought about, and was in agreement about.

So what is better as far as insulating the probe from the actual air temp in the ferment chamber, and why? Bubble wrap, or a small towel, folded 2-3 times?

Air is an excellent insulator. It conducts heat poorly. Bubble wrap has more air, and less solid, than a towel, so it would be much better for your purpose.

(Air, and other fluids, is a good heat convector. That is, you can move heat by moving the air. Hair dryers rely on the convection of heat by moving the air, not conducting through the air. But if the air is held stationary, as in bubble wrap and insulation and a down-filled coat, the heat won't get through easily).

 

[day_trippr]

I use ~4" square pads of inch thick closed-cell foam scavenged from packing cartons, pinned to carboy or keg with a 2" wide velcro strap.

I'd be skeptical about the insulative value of bubble wrap.
It certainly doesn't look like anything actually sold as insulation...

Cheers!

 

[Biscuits]

To piggy-back off of this thread...what is the consensus about wrapping the sensor in cellophane (sanitized of course) and dropped right into the fermenting wort?

 

[passedpawn]

To piggy-back off of this thread...what is the consensus about wrapping the sensor in cellophane (sanitized of course) and dropped right into the fermenting wort?

You want a thermowell.

 

[invictusbrew]

Air is actually a good insulator because it has low density. The materials used in insulation are chosen more for the properties in creating interstices, or small pockets of air.

This is absolutely correct. The reason your home insulation works so well is all the air in and around it, if you compressed the insulating material the R-Value (which is it's resistance to heat flow) would be greatly diminished... However, I would also echo that a thermowell is the best way.

 

[Gavin C]

I use insulation I had left over from my kegerator build. I figured what better to insulate than.... you guessed it, insulation.

Cold crashing the FV

 

[passedpawn]

This is absolutely correct. The reason your home insulation works so well is all the air in and around it, if you compressed the insulating material the R-Value (which is it's resistance to heat flow) would be greatly diminished... However, I would also echo that a thermowell is the best way.

Brewers have tested where to put the probe in a freezer. Turns out the time lag is WAY too slow using a thermowell, and the best place is on the surface of the carboy to minimize overshoot. I use a small jar of water/starsan, but I used to just use blue painters tape to hold the sensor on the carboy.

It seems to me that if a PID was used to control the temperature, and it was tuned with the sensor in the thermowell, that would be ideal. But most people use simple temp controls with minimal hysteresis (aka Johnson, Ranco, STC1000), and if there is a great time lag between the freezer kicking on and the temperature at the sensor dropping, the overshoot will be huge.

 

[invictusbrew]

Brewers have tested where to put the probe in a freezer. Turns out the time lag is WAY too slow using a thermowell, and the best place is on the surface of the carboy to minimize overshoot. I use a small jar of water/starsan, but I used to just use blue painters tape to hold the sensor on the carboy.

It seems to me that if a PID was used to control the temperature, and it was tuned with the sensor in the thermowell, that would be ideal. But most people use simple temp controls with minimal hysteresis (aka Johnson, Ranco, STC1000), and if there is a great time lag between the freezer kicking on and the temperature at the sensor dropping, the overshoot will be huge.

Hmm... I suppose you are right, perhaps I should not make a blanket statement like I did without thinking of all possibilities first. Touché

 

[Gavin C]

Brewers have tested where to put the probe in a freezer. Turns out the time lag is WAY too slow using a thermowell, and the best place is on the surface of the carboy to minimize overshoot. .

That's great to know. I was under the impression that thermowells were the gold standard. Was looking at getting a couple. Guess I 'll not bother now. Saved me some unnecessary expenditure. Thanks PP.

The more you know..

 

[Brewsncrabs]

I had overshoot problems in my freezer as well using a thermowell until I added a computer fan. This helped a lot but still wasn't perfect. I started pushing the fermenter against the wall of the freezer and my temp hasn't varied from my dual Ranco settings in 2 years. From pitch time to kegging, temp never varies. Friend with exact same setup solved it the same way.

 

[Wynne-R]

If you use a thermowell you are guaranteed maximum hysteresis and a big overshoot.

If the probe is in air, it will be minimum hysteresis and you will have a lot of small cooling cycles. Also a weak correlation to fermentation heat.

In between is in between. The one time I used a refrigerator I put the insulation under the probe next to the carboy and added layers until I had the compressor cycle timing I wanted. Three layers of packing tape, with the probe duct taped on top is what worked for me.

I’m not sure the insulation on the outside does much. I don’t know, I use a temperature controlled water bath now.

When I used the ‘fridge I measured the thermowell temp, the fridge temp and the temp in a liter of water. This is essentially a closed system so the average temps should be close to the same. It’s basically about timing.

 

[seventhmagus]

It seems to me that if a PID was used to control the temperature, and it was tuned with the sensor in the thermowell, that would be ideal. But most people use simple temp controls with minimal hysteresis (aka Johnson, Ranco, STC1000), and if there is a great time lag between the freezer kicking on and the temperature at the sensor dropping, the overshoot will be huge.

If you had a PID controller for your temperature, you would either need a tiny VFD or motor soft-start or you'd burn out your motor before your beer is done fermenting.

 

[doug293cz]

My take is that to minimize over and under shoot, and dueling cooling and heating cycles (if you have a double acting controller) is that you want to have a lightly insulated probe taped to the side of the fermenter. The issue is the lag time between the wort temperature and the chamber temperature, due to the high thermal mass of the wort. With a temp probe taped to the side of a fermenter, you are actually measuring a weighted average of the wort temperature and the chamber temperature. And the more insulated the probe the more weight is given to the wort temperature and the less to the chamber temperature. What you want in order to reduce the over and under shoot, is to give more weight to the chamber temperature, and less to the wort. This will cause the compressor to shut off earlier during cooling, because the chamber temperature cools faster than the wort. Likewise on heating, the heater will shut off sooner. The earlier shut off is what you want in order to reduce the over and under shooting. So, to give more weight to the chamber temp, and less to the wort temp, you want to use less insulation on the temp probe.

You want to tune your insulation and controller hysteresis such that on a cooling cycle you don't undershoot enough to cause the heater to kick on, and likewise on a heating cycle you don't want to overheat so that the cooling comes on.

Brew on

 

[doug293cz]

Having said that, I can tell you from personal experience that a thermowell is worth the expense. My brewpi controller temp swings are wider and quicker with a probe taped to the outside of the fermentor than they are with a thermowell.

Themowells work well with BrewPi because BrewPi tunes its predictive algorithms to compensate for the lag time between the beer temp and chamber temp, and to keep the beer temp from over or undershooting very much. In order to do this you need a second temperature probe measuring the chamber temp, and a small amount of computing power.

For a simple on/off controller with hysteresis, a temperature probe that gives a weighted average between the beer temp and chamber temp will provide better cycling performance. See my post above this one for more information.

Brew on

 

[hifidelity]

Everyone has a few neoprene can coozies lying around that they're not using. They make great insulators...tape one to the side of the fermenting vessel and slip the probe in the pocket created.

 

[kent7918]

That is just pure genius. Never even thought about that. Thanks!

 

[CGish]

Themowells work well with BrewPi because BrewPi tunes its predictive algorithms to compensate for the lag time between the beer temp and chamber temp, and to keep the beer temp from over or undershooting very much. In order to do this you need a second temperature probe measuring the chamber temp, and a small amount of computing power.

For a simple on/off controller with hysteresis, a temperature probe that gives a weighted average between the beer temp and chamber temp will provide better cycling performance. See my post above this one for more information.

Brew on

Ahhh, so that is why there is so much discussion. I haven't used any of the other controllers. Thank you for the clarification.

Cody