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I have fermented my last few batches with a swamp cooler - putting my bucket into an igloo cube cooler filled with water and ice. They've all been ales. I usually start in the high 60s/lows 70s (groundwater temp) and then add frozen water bottles to drop it into the mid 60s after a few hours. Quite often it seems like adding the ice makes the airlock bubbling slow down significantly. I can't be sure that it's not slowing down because the fermentation is just naturally slowing down or if it's the drop in temp. It still bubbles, but more slowly, once or twice a minute. This has happened with several different ale strains - Safale US-05, White labs Kolsch, White labs English Ale.

So can lowering temperature too rapidly result in stuck/slowed fermentation?

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Not in my experience, although it's somewhat dependent on the strain of yeast you use. Supposedly, WY3787 (Westmalle) can prematurely drop out if you chill too much too quickly (subjective terms for sure), but I use that yeast a lot and have never experienced that. I think what you're seeing is not yeast dropping out, but simply becoming a bit less active because you've lowered the temp. I wouldn't say it's a bad thing as long as you can maintain temps in the low-mid 60s. A less violent fermentation at a slightly lower temp usually produces better beer.

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I don't expect any upvotes for this answer, but to tack on to the above, bubbling or lack of bubbling doesn't not mean yeast aren't working. Also, I assume you are talking about the temp of your fermenter and not the ambient air.

If, however, you were to take a batch that was having a vigorous, visibile, BUBBLING (!) , fermentation in the 70's, then drop it in to the 50's, then you MIGHT cause the yeast to go dormant.

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