Oxygen for Yeast Starters

[cladinshadows]

Is a shot of pure O2 at the start beneficial for stirred yeast starters?

My typical starter method is to boil up some starter wort in an Erlenmeyer flask, chill it down to the 60s F, and pitch the yeast. At that point I will either just start the stir plate or I will add a 5-10 second shot of pure O2 and then start the stir plate.

Is the shot of O2 helpful? Is there a risk of overoxygenation using that method? Is there a risk of underoxygenation if the shot of O2 is not provided?

I know from experience that both methods can produce great beer, and "if it ain't broke...", but I am curious about opinions on the absolute best, most optimal method to employ. One of my "Brew Year's Resolutions" is to really dial in my oxygenation process (which includes my shiny new oxygen regulator and not-as-shiny-but-still-new oxygen tank).

Bonus question: if you were to oxygenate a starter, how much would you add? My method has been to essentially ratio down the quantity I provide in a normal batch. Typically I go with 90 seconds at 1L/min into a 20L batch. That would equate to about 7 seconds at 1L/min in a 1.6L starter.

 

[TallDan]

Based on my level of understanding, I don't see any benefit of pure o2 when you're using a stir plate.

First off, the stir plate is adding air (with oxygen) to the starter, that's what it's there for. Beyond that, the stir plate is bringing the o2 concentration of the starter into equilibrium with the o2 concentration of the air. If you use pure o2 to increase it beyond equilibrium, the stir plate is going to actually release that oxygen.

Second, the gravity of your starter should be low enough that the wort does not require more o2 than what is introduced by constant shaking/stirring.

Pure o2 is great for high gravity wort which needs a higher o2 concentration, or when the volume of wort makes shaking/stirring impractical, but just isn't necessary here.

 

[Vale71]

I'd advise you against using pure O2 afer you've pitched the yeast as O2 at those concentrations is toxic and you could be doing more harm than good. If you really want to increase yeast propagation rates and yeast vitality you should look into providing continuous aeration, for example by leaving an aeration stone in the flask and pumping air through it the whole time. I started doing it over a year ago and will never be going back as I never got such strong, clean fermentations when just using a stir plate. If you decide to give it a try then it's strongly advisable that you use an anti-foaming agent if you don't want to wipe half the starter of the tabletop. Continuously aerated starters tend to start quite strongly and turn into a veritable geyser.

 

[cladinshadows]

First off, the stir plate is adding air (with oxygen) to the starter, that's what it's there for. Beyond that, the stir plate is bringing the o2 concentration of the starter into equilibrium with the o2 concentration of the air. If you use pure o2 to increase it beyond equilibrium, the stir plate is going to actually release that oxygen.

Second, the gravity of your starter should be low enough that the wort does not require more o2 than what is introduced by constant shaking/stirring.

Thanks - those all seem like reasonable points.

I'd advise you against using pure O2 afer you've pitched the yeast as O2 at those concentrations is toxic and you could be doing more harm than good.

Thanks for the reply. I have not heard this before. One of the calculator options on Mr. Malty is for a starter that receives pure O2 at the beginning but isn't stirred. If putting O2 into the starter at the beginning were an issue I would have expected to hear about that at some point. At least in my brewery I have not seen detrimental effects from a shot of O2.

If you really want to increase yeast propagation rates and yeast vitality you should look into providing continuous aeration, for example by leaving an aeration stone in the flask and pumping air through it the whole time.

Interesting. If you're talking about stirred versus non-stirred but continuously aerated I don't think that matches up with the prevailing wisdom. Stirred starters (which is what I am doing) are generally considered to provide greater cell reproduction compared to continuous aeration and no stirring. (Take a look at Mr. Malty's starter calculator) Or are you recommending stirred AND continuous aeration?

 

[day_trippr]

iirc Chris White took wort to over 40ppm O2 with no noticeable issues (reference Yeast, somewhere around page 70).
That's over three times what I'm shooting for (~12 ppm).

fwiw, I always kick off my starters with a shot of pure O2 through a .5u stone while the stir plate is running. Mixes in pretty well...

Cheers!

 

[Jayjay1976]

I'd advise you against using pure O2 afer you've pitched the yeast as O2 at those concentrations is toxic and you could be doing more harm than good. If you really want to increase yeast propagation rates and yeast vitality you should look into providing continuous aeration, for example by leaving an aeration stone in the flask and pumping air through it the whole time. I started doing it over a year ago and will never be going back as I never got such strong, clean fermentations when just using a stir plate. If you decide to give it a try then it's strongly advisable that you use an anti-foaming agent if you don't want to wipe half the starter of the tabletop. Continuously aerated starters tend to start quite strongly and turn into a veritable geyser.

I like this idea as it would be possible to seal the opening with a two holed stopper allowing only filtered air to enter, and an airlock on the outlet to prevent any unfiltered air getting in. I've had starters become infected with only tinfoil as a cap, this seems like a better idea.

 

[SanPancho]

Ambient tops out at 8ppm. Most cited figures for yeast health are 12-16ppm.

However, as the mixing is continuous in a stir plate, you’re generally fine. Its always available to yeast as they reproduce. As well as driving off co2.

 

[Vale71]

Thanks for the reply. I have not heard this before. One of the calculator options on Mr. Malty is for a starter that receives pure O2 at the beginning but isn't stirred. If putting O2 into the starter at the beginning were an issue I would have expected to hear about that at some point. At least in my brewery I have not seen detrimental effects from a shot of O2.

I've heard this from my microbiology and yeast management teacher in brewing school in Germany and I'm quite sure it's the prevailing opinion in the branch so I think it's best to err on the safe side.

Interesting. If you're talking about stirred versus non-stirred but continuously aerated I don't think that matches up with the prevailing wisdom. Stirred starters (which is what I am doing) are generally considered to provide greater cell reproduction compared to continuous aeration and no stirring. (Take a look at Mr. Malty's starter calculator) Or are you recommending stirred AND continuous aeration?

I started testing it with stirring and continuous aeration, then I got a much more powerful pump (60 liters/minute) which made the stir plate redundant as that much air being pumped through a 2 micron stone provides plenty of stirring. There's no way the yeast can settle as long as the pump is running. This also has the added benefit of creating continuous positive pressure preventing ingress of contaminating bacteria and will also hinder most lacto strains, which is very advantageous considering that DME wort startes are usually unhopped.

 

[cladinshadows]

I started testing it with stirring and continuous aeration, then I got a much more powerful pump (60 liters/minute) which made the stir plate redundant as that much air being pumped through a 2 micron stone provides plenty of stirring. There's no way the yeast can settle as long as the pump is running. This also has the added benefit of creating continuous positive pressure preventing ingress of contaminating bacteria and will also hinder most lacto strains, which is very advantageous considering that DME wort startes are usually unhopped.

If you've got a powerful pump aerating AND stirring it sounds like you're working with the best of both worlds.

This got me thinking - what about a concept that combines a regular stir plate with continuous sterile air input into the headspace of the starter vessel? I've attached a sketch.

Overkill? Sure, but would it be at least an minor incremental improvement over the standard stir plate with foil concept?

 

[Vale71]

With larger volumes (let's say greater than 0.5 liters) the surface to volume ratio drops steeply also because of the tapered shape of an Erlenmeyer, and then you've also got the CO2 coming out of solution causing foaming and pushing everything upwards. The amount of O2 that will actually go into solution will be really minuscule. If you want to keep your wort continuously and thoroughly aerated then you really need to drop an aeration stone into the wort. Just make sure you add a lot of anti-foaming agent...