Do you measure wort or air temperature during the diacetyl rest

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alagenchev

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I am doing my first temp controlled batch and was trying to follow the brulosopher's ale schedule: http://brulosophy.com/methods/fermentation-schedules
There he states that after 2-5 days of active fermentation, he removes the probe to measure ambient temp and bumps to 75 degrees for diacetyl rest.
This is all fine and dandy, but I found some problems when trying to do this in practice.
First, this causes the controller to constantly switch between heat and cold, cycling the compressor a whole lot more than feels acceptable. This with 1 degree margin from target setting and 10 min delay on the stc1000.
When measuring the temp, i see big fluctuations. Let's say the freezer kicks in. Stc 1000 holds it to 75 and turns it off; however the air proceeds to get cooled on its own to 72. Heat kicks in ang goes past 75 to 77 by the time the freezer manages to cool back down.
Also when I got tired of watching this and taped the probe back to the fermenter, it measured actual wort temp of 77 degrees, so by measuring the air, my actual temp was off.
I have a fan running in the chamber, so I can't attribute the problems to temperature stratification.
What do you guys do instead? What's the point of measuring ambient temp for diacetyl rest?
 
I keep mine attached to the fermenter. I'm not sure what the point of using ambient is.
 
I'd probably just remove the fermenter from the chamber and let it free rise to room temp. While that was happening I might put an ale into the chamber and let that ferment for about 3 days while the lager is undergoing the diacetyl rest, then trade places with them so I could start lagering the first one as the ale would be fine at room temp then.
 
What do you guys do instead? What's the point of measuring ambient temp for diacetyl rest?

I never remove the probe from the side of the FV nor do I remove the FV from the chamber till fermentation is completed.

I've never seen the sense in that part of the @Brulosopher 's discussion on fermentation profile control. I guess it's because he uses a heat source and "The Back Box" that keeps overshoot in check.

I don't typically need a heat source inn my chamber owing to it being in a climate controlled room in my house. When I want to go from 50°F to 67°F I adjust the STC1000 to 67 and let the beer passively rise to that point. This takes a couple of days usually which is what i want. A slow steady rise in fermentation temperatures.

After a day or two and confirming terminal gravity is reached I crash then beer to 31°F in readiness for fining and kegging.

Here is a recently brewed lager's profile.

attachment.php


NB: Despite the titles which I use to enable me to enter the differing temperatures with ease in Beersmith, all fermentation is done in the primary. No racking other than to the keg after cold crashing and gelatin fining. Changes to the temperature are dictated by visual clues and measuring the gravity.
 
Thanks everyone for the replies. For those with a heat source, how do you ramp up? Using the ambient temp doesn't work for the rise for me, since it's pretty cold in my garage in the winter.

@Gavin, do you trigger diacetyl rest based on time alone or do you monitor gravity?
 
I thought diacetyl rest was only for lagering and serves no purpose for an ale. Also,I leave the temp probe out and hanging during cold crash.I left it taped to the bucket the first time and the freezer never shut off due to the warm beer (ferm temp) and froze my airlock.The ambient temp was 25 deg lower than the set temp.
 
Thanks everyone for the replies. For those with a heat source, how do you ramp up? Using the ambient temp doesn't work for the rise for me, since it's pretty cold in my garage in the winter.

@Gavin, do you trigger diacetyl rest based on time alone or do you monitor gravity?

I confirm the SG is within 1-2°plato of my planned FG before making any temperature changes. Usually closer to 1°P in fact.

I don't let the beer sit very long at the higher temperature. I've not yet been able to discern diacetyl in my lagers. I'm bad at picking out flavors though. Typically they are kegged at 2 weeks approx. following pitching yeast.

I'm not sold on a long diacetyl rest for lagers but I am far from experienced. I have a decent pipeline so my lagers typically lager and carb for a minimum of 4 weeks at 34°F before I'll drink them in any significant amounts. So far so good.

Here is a recent example. A Vienna lager. Hope it's useful

OG and FG
OG and FG.jpg

SG prior to ramping temperature from 50 to 67F
Ramping SG.jpg
 
I've done it both ways many times, it works totally fine. I'm not sure it's even worth worrying about. I originally ramped measuring ambient because it made for a more gradual change in beer temp, something I'm doubtful even matters.

That said, I still do it the old way :)
 
I've done it both ways many times, it works totally fine. I'm not sure it's even worth worrying about. I originally ramped measuring ambient because it made for a more gradual change in beer temp, something I'm doubtful even matters.

That said, I still do it the old way :)

Thanks for chiming in. I didn't mean to cast aspertions on your tried and very much tested methods, merely wanted to mention my lack of understanding of that bit that the OP referenced. I've learned a boat-load from you and your blog. hands down, best brewing blog there is IMO.:mug:
 
I thought diacetyl rest was only for lagering and serves no purpose for an ale. Also,I leave the temp probe out and hanging during cold crash.I left it taped to the bucket the first time and the freezer never shut off due to the warm beer (ferm temp) and froze my airlock.The ambient temp was 25 deg lower than the set temp.

There are quite a few English strains that are notorious for producing diacetyl, and raising the temperature for them near the end of fermentation does help significantly.

Also, while not strictly a "diacetyl rest", people like Jamil Zainasheff and others recommend raising the temperature of ales near the end of active fermentation. That encourages the yeast to fully attenuate, and to clean up the byproducts of fermentation (like diacetyl) before becoming dormant. Lots of homebrewers have taken to doing that with good results.
 
I tape my probe to the side of my bucket then cover it with a blue paper towel folded about 4 times. I e only done a diacetyl rest once and after reading Yeast I might just let the yeast clean everything up and see how that goes. I believe the point of measuring ambient temp would be knowing the beer is warm enough to increase clean up of by products. I believe Brulosopher did the temp experiment and the results were interesting.

My step father puts his probe in a bottle of water and uses that for his temp control. His fermentation was 4F above the set point on his STC. He has a light bulb as a heat source and it controls temps probably as well as my fermwrap heater just don't touch it.
 
First, this causes the controller to constantly switch between heat and cold, cycling the compressor a whole lot more than feels acceptable. This with 1 degree margin from target setting and 10 min delay on the stc1000.
When measuring the temp, i see big fluctuations. Let's say the freezer kicks in. Stc 1000 holds it to 75 and turns it off; however the air proceeds to get cooled on its own to 72. Heat kicks in ang goes past 75 to 77 by the time the freezer manages to cool back down.

-- 62-64 ambient right now in the house, but with nothing but the fan running in my box its up to 75. that's a little 4" duct blower fan in a 7cu ft freezer box. surprising. basically while fan is great for helping equalize air temp and beer temp, its also generating heat. maybe no 2nd heater needed?

--5gals of beer weighs min. 40lbs. but 7cu ft of air only ~1/2 pound. air will swing much more quickly in temp than the beer. so ambient is good for large temp changes without over/under shoot. (beer will never drop to 60 if your ambient air is always 70). but once you get to target temp, you can go with beer temp as its more stable. thats my experience.

--since most of the fermenting is done by the time you start ramping to d rest, temp stability isnt nearly as important, nor likely to produce any detectable results if it swings 2-3 degrees. you can safely widen your temp differential a bit to lower the cycling rate during d rest.
 
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