what would happen if you used a stir plate with a full fermentation?

[bummerkit]

obviously not for the entire fermentation because you need the trub to settle out at some point, but would this make for a better fermentation?

 

[Desert_Sky]

obviously not for the entire fermentation because you need the trub to settle out at some point, but would this make for a better fermentation?

No. If you watch a stirplate, it is constantly drawing air into the wort. Once you pitch you dont want anymore O2 entering your beer.

 

[bummerkit]

No. If you watch a stirplate, it is constantly drawing air into the wort. Once you pitch you dont want anymore O2 entering your beer.

but once the fermentation has started there would not be any O2 present in the carboy, you would be drawing co2 back into the wort.

 

[Kaiser]

There are a few papers out there that actually adress the subject of a mechanically stired fermentation. Since the yeast it kept in suspension you will get an attentuation that it very close to the limit of attenuation, meaning all fermentable sugars are consumed. And fermentaions in a tall commercial conical fermeter is able to produce very strong currents that keep much more yeast in suspension than you get in a carboy. The intention of these papers was to find an optimum for the circulation in a fermenter.

But due to the increased fermentation speed, you may end up with a different yeast derived character which may or may not be desired.


Kai

 

[bummerkit]

But due to the increased fermentation speed, you may end up with a different yeast derived character which may or may not be desired.

So a faster fermentation isnt a good fermentation?

 

[Orfy]

A beer is full of complex flavours quite a few of these are generated from the yeast. If you alter the performance of the yeast then the flavour are likely to be different from the standard.

I have recently had a ferment finish in under 24 hours, I'd of preferred it take 3-5 days.

 

[Ol' Grog]

I'm with chimone on this one. I've worked in labs for years and they will suck up air. Of course, it depends on the speed.

 

[ColoradoXJ13]

I'm with chimone on this one. I've worked in labs for years and they will suck up air. Of course, it depends on the speed.

In a 5 gallon batch, with a normal sized (1" or so) magnetic stir bar, you would barely see any movement at the top of the liquid and I doubt much O2 would get picked up. In the lab I work in, to grow 1L cultures, we have to put them on a large shaker at 250rpm to aerate the media properly, nobody does this with stir bars.

 

[bummerkit]

ok, lets start from the beginning. why is a stir plate benificial in a starter? maybe im just misunderstanding what stir plates are used for in the first place...

 

[Kaiser]

So a faster fermentation isnt a good fermentation?

Not necessarily. You want to stay in acceptable bounds. In home brewing fast fermentations usually mean to much yeast pitched or fermentation temps to high

In a 5 gallon batch, with a normal sized (1" or so) magnetic stir bar, you would barely see any movement at the top of the liquid and I doubt much O2 would get picked up. In the lab I work in, to grow 1L cultures, we have to put them on a large shaker at 250rpm to aerate the media properly, nobody does this with stir bars.

If you have an airlock on the carboy no air can get in and no O2 will be absorbed into the wort once all of the initial O2 is gone.

ok, lets start from the beginning. why is a stir plate benificial in a starter? maybe im just misunderstanding what stir plates are used for in the first place...

A stir plate keeps all the yeast in suspension. This means more of them can be an active part of fermentation and/or growing. If you have a vortex and covered the flask loosely with foil, you will also get the benefit of continuous aeration this more growth.

Kai

 

[javedian]

So stir plate for starter = more mixing and aeration -> faster growth, but possible off flavors. Since you only want the yeast, not the liquid, no problem. In full fermentation, you are using a starter for initial growth (reduced lag), but are primarily concerned with flavors, so you want the yeast to work normally. Is this right?

 

[Bills Brew]

So, when using a stir plate with a starter in one of those Erlenmyer flasks, you don't want to seal it with an air lock? Just cover loosly?

 

[Kaiser]

So, when using a stir plate with a starter in one of those Erlenmyer flasks, you don't want to seal it with an air lock? Just cover loosly?

Pretty much, you still want O2 to be able to get in. Since contaminating microorganisms don't have feet, they won't be able to get in if they cannot fall in.

Kai