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I've got a brew that's been on primary fermentation for 10 days and still haven't seen any activity in the airlock (again). Gravity has dropped from 1.040 to 1.014, but I'd still like to raise the alcohol content a little and am worried the beer will come out flat (much like my previous attempt).

I believe the problem is that it's too damn hot here and the yeast have been killed off, despite keeping the fermenter under an aircon vent & starting fermentation at midnight.

I'd like to drop the carboy into an ice bath to get it nice & cold, and then add more yeast. Will this work? Is there anything I need to consider?

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What style of beer, and which yeast did you use? What temperatures are you fermenting at? –  baka Mar 2 '11 at 13:33
    
Amber Ale; US-05 Safale. Yeast added initially when wort temp at 26C, most days around that temp, although some days up to 30C. –  Mark McDonald Mar 2 '11 at 14:24
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26C/78F isn't enough to kill the yeast. Actually from a growth standpoint they'd be pretty darn happy. –  brewchez Mar 2 '11 at 15:15
    
Just out of curiosity, what kind of fermenter are you using? In your previous questions you've mentioned a screw-on cap, so I would guess that the reason you didn't see any activity is because of a leak or the fermentation just finished really fast. –  Room3 Mar 2 '11 at 16:48
    
A plastic fermenter, looks just like this one: kwaree.com/blog/wp-content/uploads/2008/05/coopers-3.jpg –  Mark McDonald Mar 3 '11 at 3:15
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4 Answers 4

up vote 4 down vote accepted

You can add more yeast anytime if you like, but 1.040 to 1.014 sounds like its done fermenting to me. The beer isn't going to get much more fermented than what it is now.

The beer would have to be pretty hot for the yeast to get completely killed off.

There should be plenty of yeast left to carbonate the beer. If you really feel that yeast is the reason why your last batch didn't carbonate, then a half a pack of dried yeast rehydrated in a cup of boiled and cooled water can be added at bottling right in the bottling bucket along with the sugar solution.

Adding yeast to a cold carboy of beer is just going to force the yeast into a dormant state and shock them. So I don't understand why you would consider that. (Maybe its not clear from the ?)

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I agree. Isn't yeast actually most active around 85F or so? I don't think yeast dies until it hits 120F-140F, so unless you're fermenting in a sauna I wouldn't worry about it being dead. The reason for fermenting at lower temps isn't to keep the yeast from dying, it's to prevent off-flavors from occurring in your beer. –  Room3 Mar 2 '11 at 15:37
    
... and reduce the likelihood that other organisms (like bacteria) take hold. –  Room3 Mar 2 '11 at 15:44
    
could be that temperature fluctuations caused it to flocc. early, as well. –  baka Mar 2 '11 at 16:27
    
If it's flocculation, will a big shake do the trick? –  Mark McDonald Mar 3 '11 at 3:16
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@C4H5As Normally I'd say yes to resuspending the yeast. But you have to warm it up first. Otherwise the yeast just think hey its still cold here, lets settle out. In this case though, I am sorry to say that ferment is done at 1.014. It may get down to 1.012 or something, but that is not going to give you a noticable change in ABV. Your ABV here was largely fixed due to the OG! –  brewchez Mar 3 '11 at 13:13
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Short answer: Yes you can. You'll need to make a starter and get that yeast actively fermenting before you pour it into your main fermentor, though. That's now a fairly hostile environment, so adding them at the peak will help them deal with the low sugar & high alcohol environment that you'll be putting them in. I'd suggest a fairly neutral flavored yeast (if you're making an ale, US-05, WLP001, WY1056)

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Agreed with @brewchez.

The SG of 1.014 tells you that a lot of fermenting has already happened (though it is odd that you saw no airlock activity; what about yeast foam on the surface or stuck to the sides of the fermenter just above the liquid level?). With an O.G. of 1.040 you'd usually expect a bit more attenuation, down to 1.010 or 1.012, unless you've made a relatively unfermentable wort (lots of crystal, or high mash temp.)

Sometimes a highly flocculent yeast can be swirled back into suspension and this can help it finish off the fermentation a bit quicker.

It is possible that your fermentation happened so quickly (you say you pitched at midnight) that it was over and done with by morning time.

Probably your two biggest risks from high temperatures like this are the development of off-flavours, or having an infection set it. If your sanitation is really good you can perhaps get away with the latter. The former is very much a function of the yeast strain and I've never used S-05 so I have no idea how it behaves at high temperature (I did once find out that S-189, a lager yeast and my favourite one in fact, gave a good clean fermentation at 23C - wow!)

If you really do want to raise the alcohol strength, I would add additional sterile wort and mix or agitate it well. Even if you brew all-grain the easiest way would be to boil up some water and malt extract. Adding say 5 litres of 1.080 wort to your 20 litres of what-started-out-as-1.040-wort, would give you 25 litres of wort that would have an equivalent OG of 1.048. (though my thoughts on this are, if you are in the middle of the summer in Australia perhaps a 1.040 beer would be nicer than a stronger one)

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Need some more info. What type of yeast and what recipe is this? What temp did you ferment at? It sounds like you may be close to a FG for some styles. And may still have a leak in your system if you are getting no airlock activity. I wouldn't recommend re-pitching with that low of a final gravity, if you are just looking for a higher alcohol content you would have needed to start with a higher OG to begin with.

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