2 stalled fermentations for two different beers/yeasts - what's going on?

Question

I have two beers (recipes here and here). One is a session IPA, the other is a saison of sorts. They are two different beers fermented with different yeast, but both of them stalled.

The session IPA fermented in primary for a week using Safale US-05 ale yeast; OG = 1.046, FG = 1.026. The saison fermented in primary for 2 weeks using Wyeast 3711 French Saison; OG = 1.091, FG = 1.034.

The IPA should have finished around 1.010, the saison should have been around 1.015 - 1.020. Both fermented out much higher than expected. Here are my ideas on why:

1. It got too cold overnight (45-60F) where I ferment, causing the yeast to settle out early (and I didn't rouse them and warm them up because I thought they had just finished normally) - this seems to be confirmed in John Palmer's book How to Brew (p. 446)
2. Chlorine in the water causing the yeast to stall (I thought this just produced off flavors, but I don't know)

I don't have any other ideas. I'm leaning toward temperature control being the issue. I woke up this morning to find my 3.5 gal of stout at 58F and fermentation seemed to have pretty much stopped. I turned on the heat and roused the yeast by swirling and it's going again, back up to 68F and bubbling every 15 seconds or so.

Did my ferments stall because of the cold or could it have been something else?

PS - I should add that I made the first version of the tamarind saison last summer and FG was right on track at 1.010; that beer was fermented in August where I had AC set to 68F, and it took a week to ferment.

Answer 1

I'd stay they got crashed out with the temp swings.

Bring them up to 68°F and rouse the yeast.

Chlorine gas a low boiling point and is all but gone after a few minutes above 96°F. Chloramine different animal, doesn't boil out. And will still work as a sanitizer to rid water of bacteria / fungus. Usually the pitch overwhelms the effectiveness of the sanitizer. Yes it usually just manifests as off flavors rather than stalled fermentaions.

The only other thing would be that it is at terminal gravity and the sugars left are just not fermentable or still starch. Typical of a very high mash temp 159+

Answer 2

Temperature changes in fermenting is rarely a good thing.

For Safale US-05 the ideal range for fermenting is said to be 18-28°C (64-82°F), if the temperature drops to 45F in your fermenting space, it could very well stop the yeast activity.

I would advice to control temperature of your fermenting wort by putting a temperature controlled heater in order to stay in the correct temperature range for your yeast.

That being said, getting the temperature back up should restart your fermentation. Of course, the endured stress and temperature changes makes the yeast slower than if it didn't stall.