Stir plate on fermenter

I was wondering, has anyone here tried using a stir plate while fermenting their beers? It seems like it would decrease fermentation time but I don't know what keeping that yeast active would do to the beer. Any opinions or experiences?

Ok I realize people use stir plates for making starters but I never really figured out the point. Is it just to keep the yeast in suspension so they have more contact time with the wort?

gtpro said:

Ok I realize people use stir plates for making starters but I never really figured out the point. Is it just to keep the yeast in suspension so they have more contact time with the wort?

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That and it's constantly aerating the wort.

rcm_rx7 said:

That and it's constantly aerating the wort.

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But but... don't you use an airlock? If so, all you're aerating with is the CO2 that the yeast has put out. And I don't think you want to be sucking outside air into it, do you?

I was thinking since the fermenter has an airlock, there will only be CO2 inside the fermenter, so the "beer" wouldn't get oxygenated. I guess it might get oxygenated at the beginning of fermentation before the yeast use it all up.

frazier said:

But but... don't you use an airlock? If so, all you're aerating with is the CO2 that the yeast has put out. And I don't think you want to be sucking outside air into it, do you?

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A lot of people just use a piece of foil over the top, it still lets some oxygen in.

Stir plate would make rousing the yeast easier - instead of shaking the fermenter. Once a day would probably be enough. Its a good question, hopefully one of the gurus can answer.

Your getting to excited just make a big starter aerate then let it go. It will do its thing leave it on the primary for a month dry hop if you want to and youll be fine. Don't over complicate the process.

I agree that a big starter is the way to go - my beers have always got off to a quick start and finished where I expected them to but theres definitely advantages to rousing the yeast during fermentation - especially the bigger beers.

During the lag phase, the yeast will pick up all the oxygen in the fermenter headspace. It'll get even more with the top of the fermenter open (e.g. no airlock, bucket lid off). Like a starter, this will promote healthy yeast growth.
When the yeast is done growing, it'll start fermenting and generating CO2. This is when an airlock should be put on.
In general, the beer on the stir plate may attenuate higher. Yeast is kept in suspension and CO2, which can inhibit fermentation activity, is driven out of solution.
For beers that I really, really want to finish dry, I'll sometimes use a stir plate.

There are a few misconceptions going on in here in regards to a yeast starter, which this thread isn't even about in the first place. But, let me try to clear those up:

1. It is OK and even encouraged to constantly aerate a starter. More oxygen generally means more yeast growth which is one of the main reasons to do a starter. You're not going to drink your starter, so the affect this has on the taste of it is irrelevant.

2. Given #1, you generally do not put an airlock on a starter. You put a piece of loose fitting aluminum foil on it or one of those fancy spongy plugs. That will let the air in but keep airborne bugs out.

Ok. Now for the actual topic - I see no theoretical reason why you couldn't use a stir plate when fermenting actual beer. I'm thinking it really isn't necessary 99% of the time, though. The strength of the fermentation is usually such that beer will be getting swirled around plenty. But, if you want to get a bit higher attenuation or try and prevent a stuck fermentation, it could work. MikeSzwaya does say he uses one if he wants a beer to finish really dry. Given that it can increase attenuation, it may actually prolong fermentation rather than making it finish faster, though.

I see some practical reasons that may make it difficult. For one, you need a stir plate that can withstand the weight of your container and 5 gallons of beer. Second, I think you'd need a pretty big stir bar to sufficiently stir your entire batch. Third, you'd need the power on the stir plate to move that large stir bar fast enough. All these things are irrelevant, though, if you're doing smaller batches.