Fermentation Temp Control, ambient or carboy?

[sablesurfer]

I am working my way through a fermentation chamber build and I am wondering best way to control the temps. This will be a two chamber build with the chilling in one chamber. I totally expect the second chamber to equal or warmer than the first because it will only have a fan circulating cold air when the controller turns it on.

So...based on first chamber must maintain temp, second chamber has fan for air flow...

....do I put the temp probes in the ambient of the chamber or tape and insulate to the carboys when I they go in?

This impacts the amount of wiring I have to plan for.

ps....not sure i am ever going to ever lager in this, so would only have ales in it, but they won't always be at same temps.

 

[Bensiff]

I use a thermowell into the carboy. Ambient temperature doesn't necessarily tell you much as the beer will rise in temp during fermentation so, if you are trying to control via ambient temp make sure to still have a temp sticker on the carboy so you can make adjustments as you will find you run a differential often times.

 

[sablesurfer]

So no thermowells. I have to use the temp controllers I have and they are too thick for a thermowell. I have no problem taping them to the carboy and wrapping them in bubblewrap or something. I am just trying to wrap my head around how I'm going to make this thing work.

 

[jroot]

First you have to understand just what a temperature controller controls. Unlike what a lot of guys want to believe it does not control the temperature of the beer. It controls the temperature surrounding your fermentation vessel (ambient temp) whether it be air blowing over ice bottles or coils from some type of cooling unit. What temperature the beer has is always going to be adjusted by heat conduction through the vessels surface. Thus keeping that ambient temp as constant as possible is what you should be doing and that means placing the probe in the space it will control. Since fermentation creates heat the process really is just a guess so setting the controller to about 4 to 5 degrees below what you want at the start is what I do, adjusting it up as fermentation progresses. A thermowell is handy for monitoring but due to the extreme time lag in getting the beer adjusted its not very useful as a temp controller.

 

[day_trippr]

I suspect "a lot of guys" will disagree with all of ^that.
I certainly do...

Cheers!

 

[raouliii]

I suspect "a lot of guys" will disagree with all of ^that.
I certainly do...

Cheers!

I also disagree with jroot's thesis.

Monitoring with the probe under a layer of insulation in contact with the side of the fermentation vessel works just great. No guessing about an offset from ambient. The set temperature IS the wort temperature.

 

[jroot]

The argument really boils down to what you believe the ambient temps should be held at. A cooling unit will bring the ambient temp far below the set point before it kicks off if the probe is placed anywhere but the air space (that's the lag time to get wort to cool down). Ice bags react very quickly and greatly reduce that temp swing keeping ambient temp steady. That's how a refrigerator works. The probe is not placed in the contents but in the air space. It controls the chamber not the contents within.

 

[raouliii]

The argument really boils down to what you believe the ambient temps should be held at. A cooling unit will bring the ambient temp far below the set point before it kicks off if the probe is placed anywhere but the air space (that's the lag time to get wort to cool down). Ice bags react very quickly and greatly reduce that temp swing keeping ambient temp steady. That's how a refrigerator works. The probe is not placed in the contents but in the air space. It controls the chamber not the contents within.

I'll have to disagree again. IMO, the issue is what temperature you want the wort/beer to be held at. I prefer to not even consider it a refrigerator but a fermentation chamber with the express purpose of controlling the temperature of fermentation. If you know what temperature you want to ferment at, then control THAT temperature. It can successfully be done with little effort. Given gentle cooling, and especially heating, under/over shoot can easily be kept below 1degF.

 

[big_len]

Here's some simplified math (in mostly SI units )

Take a large freezer, say 15cu ft. That is 0.435 m^3 of air. Lets assume it's as low as the freezer can go, around -20C. At this temp the density of air is about 1.4 so we have 0.425 * 1.4 = 0.595 kg of air. The specific heat capacity of air at -20C is 1.005 so we have 0.598 KJ/K of energy. So for every degree C that the air rises, it takes ~0.6 KJ of energy.

Now consider 5 imperial gallons of wort. 5 gal = 0.0227 m^3 of wort with a density of about 1000 kg/m^3 so our mass of wort is 22.7 kg. The specific heat capacity of (lets assume) water is about 4.2 in this temperature range so our 5gals requires 4.2 * 22.7 = 95.34 KJ/K. This means that to reduce the temperature of that wort by a single degree C you need to remove ~95 KJ of energy.

So what does this mean? Say you measure the temperature of your wort in the carboy in your fridge and your set point is 60F (15.5C). Consider the worst case scenario that, at the moment that temperature is reached and the compressor switches off, the temperature of the air in the freezer is at -20C. If all the energy to raise the temp of the air somehow comes from from the wort/carboy until the two were at the same temperature, the wort would have dropped by (0.6 * 35) / 95 = 0.22C or 0.4F.

This is assuming a large freezer and in reality the air will draw a large portion of its energy from the surrounds rather than the carboy. Even still, this is below the accuracy of any temperature measuring device we homebrewers will get our hands on!

EDIT: Also I'm not trying to get involved in the discussion about which to measure: ambient or wort - just demonstrating that a bulk of cold air cannot significantly overshoot the temperature of some wort.

 

[tektonjp]

Sooo, Big Len, you're saying... um, what? Put the temp probe on the fermenter? I'm kinda slow this morning.

 

[big_len]

Sooo, Big Len, you're saying... um, what? Put the temp probe on the fermenter? I'm kinda slow this morning.

I just added an edit to explain that I'm not actually taking sides with either!

It was mentioned further up the thread about overshooting temperatures with wort measurement and I just wanted to add my theoretical 2 cents.

 

[LordUlrich]

First you have to understand just what a temperature controller controls. Unlike what a lot of guys want to believe it does not control the temperature of the beer. It controls the temperature surrounding your fermentation vessel (ambient temp) whether it be air blowing over ice bottles or coils from some type of cooling unit. What temperature the beer has is always going to be adjusted by heat conduction through the vessels surface. Thus keeping that ambient temp as constant as possible is what you should be doing and that means placing the probe in the space it will control. Since fermentation creates heat the process really is just a guess so setting the controller to about 4 to 5 degrees below what you want at the start is what I do, adjusting it up as fermentation progresses. A thermowell is handy for monitoring but due to the extreme time lag in getting the beer adjusted its not very useful as a temp controller.

I am in the disagree camp. While measuring the air is OK in practice, measuring the beer is better.

Think of it this way. When driving your car the gas peddle controls the amount of gas going to the engine and the torque the engine produces (OK a bit more complicated when you take into account computer controls and automatic transmissions but close enough). The controller (driver) does not track the torque of the engine but the speed of the vehicle. Going up hill requires a bit more power, so you give it more power to maintain speed. This is like when fermentation is going heavy and pumping out a bunch of heat.

Now in practice the fermentation temperature control thermodynamic system involves pulling heat out of the fermentation (your really don't move cold but remove heat). To do that you pull the heat from the vessel to the surrounding air. This leads to a correlation between the beer temperature and air temperature.

The last big part of the puzzle (and lots of people will hate this) the actual temperature is not that important, it is consistency in that temperature, and from batch to batch. If you know you set your system for 68 and it will produce a good ale, then set it at 68. If it is too fruity, drop it to 64 for the next batch. If you can control something to be consist ant you can change things and make improvements.

 

[Rivenin]

While everyone is right and wrong in this thread... everything works.

My setup does ambient... reason being is i have a wine fridge that controls the ambient within the fridge itself. so it's impossible to control the "beer temperature" as they are stating... For the most part with my stuff, i check it before i go to work and when i get home. but for most ale fermentations, i have the temperature set to 60* usually, sometimes 55* if it gets unruly and jumps a bit. but that keeps the fermentation right aroudn 64-65 or so.
If i was to do a cold room i'd probably try to keep the ambient around 55 or a bit above that.
But that's how MINE works, and that's my opinion everyone is going to have different ways of doing things. but it works for me....