Measuring Fermentation Temperature

[manticle]

Correct me if I'm wrong on this but doesn't the fermentation, particularly in the first few days, create heat? If so by using an offset then wouldn't the temperature be correct whilst the wort in generating heat but once the primary fermentation is over it will stop generating heat, will reach equilibrium with ambient and the temperature will now be incorrect owing to the offset?

The early part is when it's most important.

I usually start my wort about 4 degrees below intended temp, set it to around 2.5 below once pitched then often bring it up a degree or two when it's close to FG. Rest it for a few days then down to fridge temps to cold condition.

I measure the actual wort every so often to see if I'm in the ballpark - as easy as dropping a thermometer into a hydrometer tube (unless you're outside in the snow).

 

[bradsbrew]

I found that the STC probe in a PET bottle of water sealed with blue tack and placed against the fermenter works well. That way you get to measure the temperature of the liquid and not the air.

 

[stm]

I just let the probe hang near the top of the fridge and let it measure the air temp, and set it about 3 degrees below my target fermenting temp. This produces the smallest temp variation in the wort/beer with the equipment I have (fridgemate). As fermentation completes (ie, exothermic phase completes), the beer temp slowly drops to about what the fridgemate is set to.

 

[Dips Me Lid]

I've been thinking about this topic all week, at present I use a Hevac HTC-2 heat/cool controller with a standard Hevac sensor stuck to the outside of the fermentor to control the fridge/heatband. I've been looking to tighten my control on the actual temp of the liquid,
A thermowell looks like a good option to get a more accurate reading of the liquid but it seems accuracy can be a problem for an incorrectly sized thermowell, looking at this entry from wiki;

"To be representative of the average temperature of fluid, the thermowell must extend a few percent of the inside diameter of the process pipe or vessel. [1] A rule of thumb that is sufficient for most industrial applications (apx. 1% accuracy) is to ensure that the thermowell projects 5 times its own diameter into the process plus the length of its sensing element. So, for a grounded thermocouple spring loaded into a thermowell with a 1 inch diameter shank and a tip thickness of .25" a typical immersion length would equal 5.5 inches (1" OD x 5 + .25" well tip thickness +.25" sensor wall thickness = 5.5").

Apx. 1% accuracy by that rule sounds pretty good, are there any other downsides to thermowell's? Increased sanitation risk ect?


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[verysupple]

That quote is simply about how quickly the thermowell and probe can get to thermodynamic equilibrium (or near enough) with the liquid. It's about systems where the temperature may change rapidly such as if you had a thermowell in a pipe where the liquid flowing through it can change quickly. For fermentation the temperature changes very slowly and this really isn't an issue.

The only minor issue with using a thermowell I can think of is if the inside diameter of the thermowell is significantly larger than the probe such that the volume within the thermowell (which would be mostly air) never reaches thermodynamic equilibrium with the wort. That's hopefully unlikely though.

 

[Dips Me Lid]

That makes sense, a static liquid wouldn't pose the same issues, in regards to the deadspace between the inside of the thermowell and the probe I guess Heat transfer paste would work as a good conductive medium between the two.

 

[Parks]

I cut up a stubby cooler, tape it to the side of my fermenter and stick my temp probe in there.

This is exactly what I do for these reasons:

1. Measuring the actual wort temp is only beneficial at the start of the ferment when it's really generating heat. After that point you are deliberately fluctuation your temp 2 degrees around your set point.

2. Measuring air temp means unnecessarily turning your fridge on and off when you open the door.

3. Measuring a bottle of water in the fridge doesn't address wort temp at all. This option I use in my kegerator.

Ideally you would measure wort temp first then switch to something more suitable. Or have a temp controller that could turn on/off more tightly than 1 degree.

 

[manticle]

Or just pitch cool and allow gentle rising through ferment. Easy done, works well for me.

 

[Parks]

Or just pitch cool and allow gentle rising through ferment. Easy done, works well for me.

See I struggle to get my wort below 25 degrees with the chiller. I'll try to sort out a post chill ice pump thing one day...

Anyway my point is that I either wait to pitch another 2-3 hours to get from 20 to 16 or whatever or I pitch and wait it out. Lots of things to think about...

 

[manticle]

Easier for no chill I guess.

 

[Coalminer]

Easier for no chill I guess.

I normally no-chill and usually put the cube in the fermenting fridge set at the desired pitching temp - after a couple of days its ready to pitch

Whats wrong with one of these: -

http://www.craftbrewer.com.au/shop/details.asp?PID=955

They fit into an airlock grommet and connect to an stc-1000 - not expensive in the grand scheme of things

I am considering using one of these and I think it should be placed half way between the side of the fermenter and the centre to get an average reading

cheers

edit -spelling and hyperlink

 

[djar007]

I also use a jar filled with water to put the probe in. Less reactive if I need to open the door. I set it up at temp the day before so I can put the fermenter straight in. Always wrestle with the pitch too warm and stress the yeast v's wait for wort to be chilled to temp and risk an infection dilemma. Usually get it chilled close to temp and those few degrees over soon drop down in the fridge I have so I can live with myself pitching a couple of degrees over. For now anyway.

 

[Parks]

Whats wrong with one of these: -

http://www.craftbrewer.com.au/shop/details.asp?PID=955

I am considering using one of these and I think it should be placed half way between the side of the fermenter and the centre to get an average reading

My argument against using something like this is you guarantee a temperature swing in your wort up and down a total of 1 to 2 degrees (for 18 degrees it'll go down to 17, up to 19, down to 17 etc).

 

[Dips Me Lid]

Is there any data available on the average amount of heat yeast produce during primary fermentation? I realize this could probably vary a lot due to a number of reasons but is there a ballpark figure for aerobic/anaerobic phases?

 

[manticle]

All yeasts are different. I mostly operate on a 2.5 degree swing based on measurements I've taken but just like some humans can run faster than others, some yeasts can produce more or less heat than others.

Apart from that- wort gravity and composition, yeast health, yeast numbers, fermentation vessel and environment will create other important variables.

 

[Dips Me Lid]

Cheers mate, I thought there would be a lot of variables and hence no easy answer, 2.5 is a good start point though. What are common commercial brewery practices for measuring fermentation temp? I guess they have tighter deadband control and measurement than homebrewers have access to.

 

[O-beer-wan-kenobi]

Im going to add my 2c worth.

if you have a temperature controller that has a differential setting of say 0.2 degrees, you can measure the wort directly and will only get the 0.2 degrees fluctuation either side of your set temp.

I had a fridge temp controller that only had 1 degree differential, which like Park said, would give you a fluctuation from 17 to 19 degrees if your set temperature was 18.

I now use a temp controller set at 0.2 degrees differential to measure the wort and keep tighter temp control. I was concerned that there was too much fluctuation for the yeast which could stress them or maybe stall if you were fermenting on the high or low end for the yeast strain.

 

[Spiesy]

The only minor issue with using a thermowell I can think of is if the inside diameter of the thermowell is significantly larger than the probe such that the volume within the thermowell (which would be mostly air) never reaches thermodynamic equilibrium with the wort. That's hopefully unlikely though.

I drop the probe in so that it hits the end of the thermowell (which is positioned in the middle of my 30l fermenter, and goes down about halfway). Stainless on stainless - I'd imagine that translates a reasonably accurate temperature of the surrounding wort.

 

[jkeske]

I know this site thrives on conjecture and hearsay, so I hope I don't break the mold with posting actual data. But yes yeast is exothermic (heat generating) during fermentation, and can raise the fermentation temperature buy several degrees over the ambient temp. The attached examples were done in a chest freezer controlled by a brewpi (www.brewpi.com). The wort temperature during early ferment is significantly higher then the surrounding air. A fan in the freezer would have probably equalized the temp a bit, but it clearly shows that where you are measuring your temp makes a difference

 

[djar007]

That is awesome jkeske. Says it all. Now I am rethinking the glass of water with a probe in it. Because obviously a glass of water is not equal to a glass of fermenting wort. Pretty obvious I guess.