S-04 Fermenting Cold

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Iron Wolf Brewery
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I've put on a part-mash porter recently and for want of a better ready-to-pitch yeast, chucked in rehydrated DCL S-04. It's now fermenting at about 16-17C. Normally when using this yeast, I've fermented at 20-21C but the recent cold snap has prevented this. Does anyone have any experience that might tell me what to expect?

As a side note, I only put 1Kg of extract into 2.8Kg of grain wort. OG at pitching was 1.040. I planned to add another 1 or 1.5Kg of DME once fermentation took off (which it now has - active bubbling). I was thinking to add the extra wort still a bit warm to raise the temp by a degree or two. Feedback appreciated.

Hi PoMo,
I have only just started using liquid yeasts and before this I used SO 4 for all my ales.
Its recommended temp is 18 deg and if you added extra wort the temp may come up by itself due to fermentation temperature.
I have never deliberately fermented it at 16 or 17 deg but i would imagine that it would not effect it apart from it may be a little slower.
This yeast is generally a quick worker and ferments out very clear if kept below 20 deg from my observations.
I dont think you will have any problems!
Yeasties are amazing things... I've got a Wyeast 1028 fermenting away merrily at between 12 and 14 degrees at the moment. I've only just put the heater belt on it but the yeast doesn't seem to mind. No one seems to mention problems with fermenting too low (except maybe stuck ferments). I'd ride it out and let the little buggers do their work.

My 2 bobs worth,

Hmmmm I wonder where ferment temp is being measured? Outside of fermenter or in the middle of the active wort?

Leave adding a heat source (belt, pad or light in insulated box) until you have tried wrapping the fermenter in a blanket

Jovial Monk
I just go off the stick-on fishtank type "fermentometer". I noticed it had crept up to about 18 by itself yesterday. I added the extra litre of wort (with just over a kilo of dme) at pretty close to room temp - maybe 20C - and gave it a good stir with sterilised brew paddle. The airlock is still bubbling away nicely.

Another fermenter sitting beside it has finished brewing a 1.039 wort down to 1.009 with WLP007 at much the same temp. Looks like it's all good. Better too cold than too hot, I'm finding!
S-04 can produce a lot of diacetyl if fermented too cold, and heaps of esters if fermented above about 20C (even though DCL's recommended temp is 18-24).

I'd try to keep it somewhere in between 17-21.
So would a diacetyl rest after primary be called for?

Just keep the temp in between 17-21 to allow the yeasties to gobble up any diacetyl, and to keep the them from flocculating early.

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