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So I understand that going above the optimum yeast temperature specified is a bad thing and will cause major off flavors.

But what happens when you go underneath it?

For example, I am currently using a Wyeast 1214 Belgian Abbey from NB which specifies the optimum temperature range as 68-78*F.

My tendency is, around 3pm, when I start to feel warm, to grab 5 frozen water bottles and throw it in my swamp cooler.

I just rigged up a temperature monitoring apparatus this morning and have been measuring the temperature all day. When I started to feel warm, the temperature in the swamp cooler was only 72F, and now after I threw in 5 frozen water bottles, the temperature in the swamp cooler is 60F (now it is actually 59.8F!) (now 57.7F)

What are the consequences of my actions for doing this to an Ale?

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Can you measure the temp of the beer? E.g. tape a thermometer to the side of the carboy with insulation. The temp of the swamp cooler doesn't tell you much and will certainly not be the same as the beer. –  mdma Jun 20 '13 at 23:26
    
Agreed with mdma, the temp of the cooler water is not the same as the beer temp. Also, how long has this beer been fermenting? Temperature is most critical during the first few days of fermentation. After that the temp is still important but not as critical, since the bulk of sugars have been consumed. –  Galapagos Jim Jun 20 '13 at 23:33
    
@MDMA Would you please elaborate on taping a therm/ to the side of the carboy with insulation? I have a tea-shirt over the carboy; would that provide enough insulation (I assume it won't)? What material should I use? –  Matthew Moisen Jun 20 '13 at 23:59
    
@GalapagosJim This particular carboy has been fermenting for a week and a half; however, I was especially good during the first few days of fermenting at putting 5 frozen water bottles in the swamp cooler at regular intervals. –  Matthew Moisen Jun 21 '13 at 0:01
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3 Answers

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You're measuring the temperature of the swamp cooler water and not the beer, and the beer will take a long time to reach the cooler water temperature, which will also rise in temp during the same period. This is because heat transfer between the beer and the cooling water is slow, since the surface area is small compared to the volume, plus both liquids are not in motion.

So, what I expect will happen is that the beer temp will drop in a few hours, but no where near the drop from 75F to 60F. Probably somewhere in the middle - 66-68F at a guess. So I think the yeast will be fine.

But what would happen if you really did drop the temp to 60F? The yeast would drop out of the beer and stop fermenting, leaving a high FG/low attenuated beer.

After the first 3-5 days of fermentation (depending upon activity level) it's a good idea to slowly raise the temp of the beer to 72-74F so that the yeast are encouraged to continue fermenting and not drop out. This will give you a better attenuated beer that often requires less conditioning time. The increased temperature doesn't give the off-flavours you mentioned, since the bulk of fermentation is now complete - the yeast are much less active and produce far fewer flavor compounds.

EDIT: As you see, Denny and I have different perspectives, and unless you have a probe immersed in the beer, you don't really know what the fermentation temperature is. While one yeast strain may tolerate a drop to 60F or lower, another may stall at that temperature. Either way, it's not usually a crisis, just rouse the yeast and raise the temp and fermentation will typically pick up again. But ideally you should be looking for a more even temperature - avoid temperature swings. You can try adding just a single bottle more frequently, rather than dumping 5 in at once.

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You recommend raising the temperature after the first several days of fermentation; is that a general recommendation, or something applicable to this particular situation? –  object88 Jun 21 '13 at 15:04
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If you have temperature control, it's a general recommendation for most ale yeasts, particularly if they have a relatively high minimum temp (e.g. 68-70F.) For more hardy ale yeasts, like WLP001/WY1056/S05, it doesn't really matter, since they are typically fermented well above their minimum. –  mdma Jun 21 '13 at 16:14
    
Just to be clear - I'm not saying you can't ferment at 60F, if that was the constant fermentation temperature from the outset, but rather, that you should not drop the temp from 72F to 60F as there's a good chance the yeast will drop out from the temp decrease. –  mdma Jun 24 '13 at 0:09
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The yeast will not necessarily drop out at 60F. I've used 1214 at that temp many times and I find it preferable to fermenting it at higher temps. In fact, I prefer fermenting pretty much any ale (and many lager) yeasts at or below the lower end of the temp range. You get cleaner beer with fewer esters and phenolics. I often ferment WY1007 and 1728 in the low to mid 50s, despite the manufacturer's recommendation of almost 10 degrees higher. IMO, all the temp ranges listed by yeast companies are higher than what I prefer. Wyeast sells one strain of yeast that I gave them (WY1450) and the temp range they have for that is at least 8F higher than what I actually use! The exact behavior will depend on which yeast strain you use, but in general there is nothing wrong with fermenting somewhat below a yeast's listed temp range.

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If I understand correctly, fermenting at a lower temperature will slow the yeast down, so it will just take longer to get through all the sugars? –  object88 Jun 21 '13 at 15:51
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Yes, that is correct. And "longer" is completely variable. –  Denny Conn Jun 21 '13 at 16:15
    
WY1214 is notorious for dropping out if the temperature takes a downward turn. You're talking about ambient temp - I'm talking about beer temp, which will often be 10F above ambient. So a ambient temp of 60F is not the same as a beer temp of 60F. –  mdma Jun 21 '13 at 16:20
    
Have you had that happen to you? I have used 1214 many times and have had no difficulty fermenting it at a beer temp of 60F. If it gets above 64, it throws so many banana and bubblegum esters as to make the beer unenjoyable IMO. –  Denny Conn Jun 21 '13 at 16:47
    
It's not the ferementation temp that's so critical, but the temperature swing downwards. Sure you can ferment many yeast under the specified range if you hold the temp constant, but if you suddenly drop the temp from 72F to 60F there is a good chance the yeast will drop out and not finish up, particularly if this is towards the end of the ferment when there is less food available. –  mdma Jun 24 '13 at 0:04
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Fermentation temperature - Keep it constant. Encourage the properties you want to accentuate with the yeast to complement the style. Monitor the results, that way if you think the recipie is worth trying again, make the relevant adjustments, like you would with the recipie. Small temp variations have a great impact on results. Phenolic yeasts should be free to rise and fall on their own account preferably within a predictable/constant ambient temp. Too low, clear beer, what about character then?!

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