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I don't have a fermentation fridge so I have to put my fermenter in the best spot to get the correct temperature; and keep an eye on it and move it or heat/cool it if necessary. My last brew I used Safale US-05 and I was aiming for a starting temperature of 16°C letting it rise to around 22°C after 3 days and holding it around 20/22 °C to the end, which I understand is a good profile for the yeast.

However to cut a long story short and my "cold" room was too cold and my "warm" room was too warm and the beer ended up sort of swinging from 12°C to 22°C a number of times, but this is still within the Fermentis recommendations, in fact it was mostly between 15 and 22 which is what they say it should be ideally.

FERMENTATION TEMPERATURE: 12-25°C (53.6-77°F) ideally 15-22°C (59-71.6°F)

My question is does it have to be a consistent temperature as well as being between 12°C and 22°C ... and if it does what negative effects would a fluctuation in temperature cause?

I think there were probably 3-5 signifignant cyles of 12/15 °C to 20/22 °C and back again

US05 PDF - http://www.fermentis.com/wp-content/uploads/2015/12/Safale-US-05-en.pdf

EDIT it just occurred to mention my gravity readings, which surprised me a bit but not sure. The fermentation went from 1058 to 1012 in 5 days

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"does it have to be a consistent temperature" - IMHO, no.

"what negative effects would a fluctuation in temperature cause" - very few unless the temperature was mainly tending to the high end of the range. Then it might give a more fruity flavour to the brew - which is not a bad thing but may not be what one wants. If the temperature dips too low for a longer time then the beer may cool and will only warm slowly. The lower temperature may produce a "cleaner/crisper" beer but will usually inhibit the yeast and so will require longer to ferment. Its a case of "swings and roundabouts". While the mentioned 3 thermal cycles between 12 and 22 may have some effect I doubt it would seriously detract from an otherwise fine brew. And I also doubt it will it turn an otherwise bad brew into a good one!

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  • thanks - I should have put in my question ( doing it now ) that the beer also fermented much faster than I had expected - went from 1058 to 1012 in 5 days; now sure whether that's OK or an indicator of anything else
    – byronyasgur
    Nov 24, 2016 at 18:52
  • The quoted drop in SG over a period of 5 days is not unreasonable. I personally would not bottle or transfer the beer before 14 days in the fermentation vessel - whatever the SG. Then I would bottle it - whatever I thought it initially tasted like. From the comments above, I doubt there is anything wrong with the brew.
    – barking.pete
    Nov 24, 2016 at 19:13
  • ok that's cool I might do that - it fermented so fast I never got to dry hop it
    – byronyasgur
    Nov 24, 2016 at 19:17

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