Ambient vs Fermentation temps with a chest freezer

[cdburg]

I'm definitely not trying to stir up shit here, but I did want to post an example of what I was talking above with my experience with a glass carboy in a freezer for fermentation.

The picture below (not great, but hopefully visible) shows the difference in temperature between a probe taped to the outside of the glass carboy (insulated with silver, reflective bubble wrap) and a probe in a thermowell in the middle of the fermenting beer.



In this case, I was fermenting a Kolsch at 60F. The "Cool" Ranco controller is the probe in the thermowell (running the freezer). The "Heat" Ranco controller is the probe that was attached to the outside of the carboy (for comparison).

In this case, the freezer was running, to knock the temperature back down to 60F from 61F. In the process of cooling the beer, the first thing to cool is the glass carboy, like a bottle of beer in the fridge. In this picture, there is a 5 degree difference between the two probes.

When the freezer isn't running, the two temperatures are usually very close or the same. When the freezer kicks on though, the "outside" probe reaches the desired temp (60F in this case) about 20 minutes before he internal probe. If I used that to control the ferment, it wouldn't be quite as accurate. The liquid wouldn't be cooled to the desired temp, and could get quite warm over time. I actually had problems with fusels in the past before I moved to the thermowell.

As always, your experience my vary, but I've found the thermowell to be more accurate and to produce better beers, in my set up. If you use a refridgerator to control temps (as Jamil does), I don't think it would be as much of an issue since the liquid would be cooled slower. If you ferment in buckets or plastic carboys, I also don't think it would be an issue, since plastic is a better insulator. For glass carboys fermenting in freezers though, I would encourage everyone to test for themselves. You might see something similar to what I have experienced.

[andy77]

I'm definitely not trying to stir up shit here, but I did want to post an example of what I was talking above with my experience with a glass carboy in a freezer for fermentation.

The picture below (not great, but hopefully visible) shows the difference in temperature between a probe taped to the outside of the glass carboy (insulated with silver, reflective bubble wrap) and a probe in a thermowell in the middle of the fermenting beer.



In this case, I was fermenting a Kolsch at 60F. The "Cool" Ranco controller is the probe in the thermowell (running the freezer). The "Heat" Ranco controller is the probe that was attached to the outside of the carboy (for comparison).

In this case, the freezer was running, to knock the temperature back down to 60F from 61F. In the process of cooling the beer, the first thing to cool is the glass carboy, like a bottle of beer in the fridge. In this picture, there is a 5 degree difference between the two probes.

When the freezer isn't running, the two temperatures are usually very close or the same. When the freezer kicks on though, the "outside" probe reaches the desired temp (60F in this case) about 20 minutes before he internal probe. If I used that to control the ferment, it wouldn't be quite as accurate. The liquid wouldn't be cooled to the desired temp, and could get quite warm over time. I actually had problems with fusels in the past before I moved to the thermowell.

As always, your experience my vary, but I've found the thermowell to be more accurate and to produce better beers, in my set up. If you use a refridgerator to control temps (as Jamil does), I don't think it would be as much of an issue since the liquid would be cooled slower. If you ferment in buckets or plastic carboys, I also don't think it would be an issue, since plastic is a better insulator. For glass carboys fermenting in freezers though, I would encourage everyone to test for themselves. You might see something similar to what I have experienced.

You're not stirring things up, good data point.

This would be my question: if you're controlling the temp via a probe taped to the side, what's the actual temp swing of the wort. If the measured temp swings from (in you example) from 61, back down to 60 very quickly because you're measuring the glass temp, then everything equalizes, then the fridge turns back on again and cools back down again very quickly, the wose case scenario is overcycling the fridge. But if the actual wort temp, over the long term stays at 60-61 then that's a good ferment.

Remember that the goal isn't to measure the fermentation temps exactly, but to maintain a desired temp through a whole fermentation.

At any rate, I tape to the side of the carboy, and have great fermentations.

[cdburg]

You're not stirring things up, good data point.

This would be my question: if you're controlling the temp via a probe taped to the side, what's the actual temp swing of the wort. If the measured temp swings from (in you example) from 61, back down to 60 very quickly because you're measuring the glass temp, then everything equalizes, then the fridge turns back on again and cools back down again very quickly, the wose case scenario is overcycling the fridge. But if the actual wort temp, over the long term stays at 60-61 then that's a good ferment.

Remember that the goal isn't to measure the fermentation temps exactly, but to maintain a desired temp through a whole fermentation.

At any rate, I tape to the side of the carboy, and have great fermentations.

From what I can tell, the beer temp isn't reducing for the externally mounted probe. The "outside" probe hits a 1 degree drop in temperature pretty quickly, probably in about 15 minutes. To drop the thermowell probe temperature 1 degree, it takes more like 45 minutes to an hour. In 15 minutes (the time the freezer would run with the external probe location), I don't think the temperature of the beer is dropping too much. I also don't think the glass gets cold enough to drop the beer any further, so I don't think that everything is equalizing at the correct temperature. I actually think that the internal temperature is increasing, since it's not being cooled enough to maintain the correct temp.

To me, it seems like the outside probe is measuring the temperature of the glass, not the beer. When the freezer is not running, it's generally fine, since the glass is roughly the same temp as the beer. When it's being cooled though, measuring the temp of the glass and not the beer seems like it could be inaccurate. Over time, I believe it builds upon itself. I think that is compounded with an especially aggressive yeast (e.g. belgian strains).

To be fair, I am in California, and it gets warm in the room where the freezer is located. The freezer is fighting external temps also, so if it isn't running long enough to cool the fermenting beer, the fermentation can get out of control pretty quickly. I think that's exactly what was happening to me. I was getting fusels. I could taste them, and I got dinged on several judging sheets for them. Those beers fermented at the low end of the temperature range, according to the external probe, but they still ended up tasting hot. Combining that with the temperature difference I showed in the picture, I have a reason to believe the temperature measured with the external probe was inaccurate enough to cause issues.

As with everything, my experience is just that, my personal experience. I just wanted to throw out an example where the external probe mounting may not be ideal. I've learned that I get better control and better beers with a thermowell. For $14.00 (http://www.brewershardware.com/16-Stainless-Steel-Thermowell.html) and the price of a carboy hood, I know that my temperature is where I want it. It's definitely worth the price to me.

[BrewChemistinCO]

What step of fermentation is your yeast in? If you just pitch and you are going nuts then you should have a fair amount of circulation in the beer. I would bet that both the therm well and the outside glass temp are fairly similar.

If you have made it past the first few days or are conditioning then I would bet you see more variety. The thermal mass of the beer is pretty significant and the outside layers of your beer have probably dropped but your therm well is reading rig in the middle which would be the last to change.

The idea is similar to the jamil style wort chiller. Circulation causes quick heat transfer.

[cdburg]

What step of fermentation is your yeast in? If you just pitch and you are going nuts then you should have a fair amount of circulation in the beer. I would bet that both the therm well and the outside glass temp are fairly similar.

If you have made it past the first few days or are conditioning then I would bet you see more variety. The thermal mass of the beer is pretty significant and the outside layers of your beer have probably dropped but your therm well is reading rig in the middle which would be the last to change.

The idea is similar to the jamil style wort chiller. Circulation causes quick heat transfer.

The temperature difference I showed in the picture has happened at all parts of the fermentation. Any time the freezer turns on to cool the beer, there is a lag in the time it takes to drop the beer temperature (thermowell probe) versus the carboy temp (external probe). That lag time leads to a temperature difference between the probes (the carboy gets colder than the liquid inside it).

The freezer definitely cycles more when the fermentation is at or near its peak, but the temperature lag and resulting differential is the same throughout.

[ultravista]

cdburg - will you post photos of the probe & thermowell together? I am confused as to how the two fit together. How far into the wort is the probe - top, bottom, middle?