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I've read tidbits how that after the first 3 days of fermentation, you would ideally raise the temperature of the carboy for the remainder of the brew.

How, exactly, does one do this?

Say the Wyeast I buy states an optimal temperature range of 60-72*F (15.5 to 22.2*C), and I don't know enough about the flavor profile at different temperatures of a yeast, so I arbitrarily decide that the midway point is going to be my target temperature.

For the first three days I hold the temperature at 66*F (18.9*C).

Given that (I've heard) only 50% of the batch is brewed in the first three days, why would I want to raise at all?

Assuming I want to raise,

1) Do I raise after 3 days or some other amount? (Rule of thumb here as I'm not going to take gravity readings)

2) how much do I raise the temperature by?

3) how many hours/days do I take to raise the temperature?

4) do I hold it at this temperature for the duration of the brew?

Incidentally, I have 8 carboys going but only 4 fermwraps. Four of the carboys are closer to the end of the brew, and four of them are closer to the start. Is it more important for me to raise the temperatures towards the beginning of the batch that to maintain a raised temperature at the end of a batch?

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Raising the temperature during primary fermentation should be calculated by attenuation. What did Wyeast list as the attenuation of the yeast? –  Scott Mar 25 at 4:29
    
@Scott I have four relatively new batches that state around 72-77% attenuation. –  Matthew Moisen Mar 25 at 4:58

2 Answers 2

1) Do I raise after 3 days or some other amount? (Rule of thumb here as I'm not going to take gravity readings)

Assuming you aren't taking gravity readings, therefor you aren't examining the apparent attenuation, your best bet is to wait until after high-krausen. This really depends on the gravity of the beer, what yeast your using (ale vs. lager, fast fermenting vs. slow, high attenuation vs. low), and what temperature you're fermenting at during high krausen. If you're fermenting on the cold end of the recommended fermentation temperature it may delay this by a day or two. Your best bet is to wait three days, check to see if the most vigorous phase of fermentation has concluded, and raise the temperature if necessary, or wait another 12-24 hours before checking again. I typically wait until the 96 hour mark (post yeast pitching) before checking.

2) how much do I raise the temperature by?

Go to the high end of the recommended temperature of the yeast, potentially ~2°F over the recommended high. Ester formation towards the tail end of fermentation will be drastically lower than it is at high-krausen, so it's okay if you overshoot it by a couple of degrees for the sake of finishing out the fermentation.

3) how many hours/days do I take to raise the temperature?

You'll need to check the gravity at this point to know for certain, but chances are, you should likely only stay at this temperature for 48-72 hours tops before lowering it back down again. Once your gravity stabilizes for 48 hours, it's best to assume that fermentation has completed. If you aren't checking gravity, best to likely assume 48 hours.

4) do I hold it at this temperature for the duration of the brew?

No. Once fermentation completes and the gravity remains consistent for 48-72 hours, you're good to bring it to room temperature, assuming that isn't < 60°F or > 75°F (for standard Saccharomyces cerevisiae).

If you have a fermentation chamber (e.g. chest freezer) to store the carboys in, you can always tape one or two of your FermWraps to the inside walls of the freezer instead of wrapping them around the carboys. That would help heat the entire chamber and not individual carboys. That of course assumes all carboys inside are on the same fermentation schedule, using the same yeast, pitched around the relatively same time.

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The main point of raising the temp is simple. As the sugars become limiting the yeast begin to enter a dormancy phase. As yeast slow down the temp of your fermentation begins to lower too. That lowering temp is also a signal to yeast to go dormant. This causes a cyclical effect of potential having the yeast drop out sooner than you want and you do not attain the most attenuation as you could have. By raising the temp a few degrees as fermentation visibly slows, you help keep the activity level up as the most robust portion of your yeast population continues to ferment what little sugars remain.

There isn't a rule about how to do it. A myriad of paths exist to affecting the final outcome of the flavor and yeast performance, albeit subtle changes between paths.

There isn't an answer for the right way to do it. You do it one way and see if it works for you when you taste it. If not try it another way.

I didn't put any #s in this answer because its something that has to be determined on a personal basis. I know what works for me, but that isn't an absolute. It depends on ambient temps, OG, beer style, yeast strain, O2 levels... etc. This, like many things in brewing, requires experimentation.

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+1 "is also a signal... causes a cyclical effect" Yeast seem to be impressive little beasties, but they sometimes appear like they just don't want to help us. I like to think about that as I eat there dead cousins in Marmite. –  Another Compiler Error Mar 25 at 13:22

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