Stir Plate or Aerate?

[jrubins]

So, my next step in brewing adventures is making proper yeast starters. I was looking at properly aerating my wort, also, using an aquarium pump.
My question: do I actually *need* a stir plate or is the main purpose of the stir plate just to aerate things anyway, because if it is, then why not just use the air pump and diffusion stone? Aerating with a pump seems to be the more "direct" route and it doesn't require any new equipment.

If aerating is better (or at least as good), what's the optimal method -- pump the whole duration of starter fermentation or pump at the beginning or ... ?

Thanks,
JR

 

[LandoLincoln]

Stir plates/stir bars are more important than aeration stones and pumps.

You can sufficiently aerate a batch of beer just by sloshing it vigorously for about two minutes.

Stir plates aren't to aerate the starter wort. They're to keep the yeast moving about.

(source)

 

[Homercidal]

They are not for the same thing. Stirplates are for building up a large quantity of yeast in a starter.

Aeration is for adding Oxygen to your wort so the yeast can grow in the fermentor.

Both are good practices, and both are pretty much dependent on liquid yeast use.

If I had to pick one over the other in importance, I would choose the stirplate and get a nice big batch of healthy yeast going. You can do this without a stirplate, but from the numbers I've read you won't get as much yeast and the stirplate makes it super easy to get as much as possible.

 

[jrubins]

Cool. Thanks for the feedback, guys. I guess my next question is why? What else is a stirplate doing when it's spinning the yeast around... making them dizzy?

 

[LandoLincoln]

It keeps them from laying on the bottom of the flask, being lazy bums. Yeast are like teenagers. They're shy. They need encouragement to get out there and mingle.

 

[trentm]

So, my next step in brewing adventures is making proper yeast starters. I was looking at properly aerating my wort, also, using an aquarium pump.
My question: do I actually *need* a stir plate or is the main purpose of the stir plate just to aerate things anyway, because if it is, then why not just use the air pump and diffusion stone? Aerating with a pump seems to be the more "direct" route and it doesn't require any new equipment.

If aerating is better (or at least as good), what's the optimal method -- pump the whole duration of starter fermentation or pump at the beginning or ... ?

Thanks,
JR

Continuous aeration throughout the starter propagation is key to getting the healthiest yeast and the highest cell counts. The problem with using a pump and stone is foaming. If you try it, you will see the flask will quickly foam over, forcing you to shut off the pump. Contrary to what some believe, if you stir your starter at high speed, making sure the vortex is reaching all the way down to the stir bar, it will bring enough air into the culture to provide adequate and continuous aeration. Also, if you stir fast enough there will be no issue with foaming or krausening as the stirring action will drive off the CO2 while bringing in O2. A stir plate simulates a shake flask which is a tried and true lab technique for propagating almost any aerobic microorganism. As an added bonus the continuous agitation will help expose all the yeast cells to most possible nutrients available in your starter media.

Let me add why you need continuous aeration: Yeast use O2 to synthesize sterols which are important to healthy cell walls. Healthy cell walls allow the yeast to reproduce more. Also the cell wall regulates the nutrients that come into the cell and waste products (including ETOH) that move out. Each time a cell buds it shares it's sterols with the daughter cell, so each has half of the what the mother cell had synthesized in the presence of O2. So if more O2 is not available the cells quickly have a deficit of sterols, the cell walls become thick and leathery, with challenges in reproduction, taking in nutrients and removing waste.

 

[JustLooking]

Stir plates aren't to aerate the starter wort. They're to keep the yeast moving about.

Not exactly.

From Mr Malty:

The stir plate causes several things to happen. One is that it drives off the CO2 (which suppresses yeast activity) and allows for an exchange of air into the starter (increasing oxygen levels) and eliminates dead spots in the starter liquid, ensuring that the yeast have easy access to the sugars.

 

[LandoLincoln]

if you stir your starter at high speed, making sure the vortex is reaching all the way down to the stir bar, it will bring enough air into the culture to provide adequate and continuous aeration.

I'm not sure how one aerates without air. During yeast propagation in the starter, CO2 is created, and since it's heavier than air, it's going to push the air out of the flask leaving a blanket of CO2 on top of the wort. So you'll be reintroducing CO2 back into the wort maybe, but not air.

 

[jrubins]

It keeps them from laying on the bottom of the flask, being lazy bums. Yeast are like teenagers. They're shy. They need encouragement to get out there and mingle.

LOL
I'll play some Taylor Swift tunes to get them on the dance floor

 

[trentm]

I'm not sure how one aerates without air. During yeast propagation in the starter, CO2 is created, and since it's heavier than air, it's going to push the air out of the flask leaving a blanket of CO2 on top of the wort. So you'll be reintroducing CO2 back into the wort maybe, but not air.

I know it doesn't seem to make sense but it is tried and true method. This article quantifies it with a shake flask system and I believe a stir plate simulates this this system. After all the shake flask is just shaking instead of stirring. When stirring fast enough it really resembles a shake flask. Notice the faster it is shaken (to a point) more O2 can be measured in the culture medium. And of course you need a closure that will allow the gases to exchange.

http://aem.asm.org/content/17/2/286.full.pdf+html

 

[k1ngl1ves]

Cool. Thanks for the feedback, guys. I guess my next question is why? What else is a stirplate doing when it's spinning the yeast around... making them dizzy?

Mostly pissing my wife off with that "dink dink dindink" sound.


So now it sits in the downstairs bathroom...