Starter areation NO stirplate

[Dusan Kovacevic]

Hi all

I remember seeing sporadic coments where people mentioned they are areating their starters with inline sterile filter and stone.

I even have a recolection of Martin Brungard saying he's doing it but I can't find that thread or any similar.

Now, I know about "shaken, not stired" method. But I would like to know is anyone areating their starters and if they have any wisdom on the process to share?

 

[IslandLizard]

Sure you can bubble (filtered) air through the starter for days, instead of stirring. The oxygen-rich beer keeps the yeast in propagation mode. Use a drop of Fermcap-S in the starter wort to prevent excessive foaming. But keep an eye on it, you may still get quite a bit of thick heavy foam, due to the small bubbles from the stone. I get that during the 30' of oxygenating the starter that way, before putting them on the shaker for their 2-3 day propagation run.

 

[Dusan Kovacevic]

Sure you can bubble (filtered) air through the starter for days, instead of stirring. The oxygen-rich beer keeps the yeast in propagation mode. Use a drop of Fermcap-S in the starter wort to prevent excessive foaming. But keep an eye on it, you may still get quite a bit of thick heavy foam, due to the small bubbles from the stone. I get that during the 30' of oxygenating the starter that way, before putting them on the shaker for their 2-3 day propagation run.

Thanks for the explanation but I have a couple of questions there.
Wouldn't 12-18 hours be enough for propagating yeast, as in that time they are supposed to reach their max density for the medium they're in?
I remember seeing a picture of areation stone dangling above the worth, but I see you are submerging it, any toughts on that?

 

[IslandLizard]

Thanks for the explanation but I have a couple of questions there.
Wouldn't 12-18 hours be enough for propagating yeast, as in that time they are supposed to reach their max density for the medium they're in?
I remember seeing a picture of areation stone dangling above the worth, but I see you are submerging it, any toughts on that?

Most books say 12-18 hours but counting from exactly where?
For most of my older yeast reserves (6-12 months in the fridge) that's clearly not enough. I don't get the color change I'm looking for, in that short time.

I wait for the color to change from (darker) brown to a much lighter color, becoming to look creamy. That can take 24 hours, even with "fresh yeast" from my LHBS, which is usually 3-4 months old, and up to several days for older, harvested, and not so fresh yeast. I give it another 12-24 hours from there. That always works well for me.

I guess you could "pump" air into the headspace while it's on a stir plate. The O2 gets dissolved, transported to the suspended yeast, while it sheds the CO2 that gets created in the process.
But without continuous agitation, by putting it on the counter and swirling from time to time, it's surely not optimal even if there's an airstone in the headspace.

So, agitation will be paramount, either way, to get the exchange of gases while keeping the yeast suspended, so it can assimilate the O2. Without continuous or intermittent stirring, keeping the starter in motion with air bubbles from the stone on the bottom, is probably the next best thing. Just watch out for excessive foam build up and foam overs. If need be turn the air supply down until there's a balance.

 

[Dusan Kovacevic]

Most books say 12-18 hours but counting from exactly where?
For most of my older yeast reserves (6-12 months in the fridge) that's clearly not enough. I don't get the color change I'm looking for, in that short time.

I wait for the color to change from (darker) brown to a much lighter color, becoming to look creamy. That can take 24 hours, even with "fresh yeast" from my LHBS, which is usually 3-4 months old, and up to several days for older, harvested, and not so fresh yeast. I give it another 12-24 hours from there. That always works well for me.

I guess you could "pump" air into the headspace while it's on a stir plate. The O2 gets dissolved, transported to the suspended yeast, while it sheds the CO2 that gets created in the process.
But without continuous agitation, by putting it on the counter and swirling from time to time, it's surely not optimal even if there's an airstone in the headspace.

So, agitation will be paramount, either way, to get the exchange of gases while keeping the yeast suspended, so it can assimilate the O2. Without continuous or intermittent stirring, keeping the starter in motion with air bubbles from the stone on the bottom, is probably the next best thing. Just watch out for excessive foam build up and foam overs. If need be turn the air supply down until there's a balance.

Yeah, I guess high krausen would be the perfec time for pitching the starter, whenever that happens.
I was reading, in other forums, about how continuous stiring is stressing the yeast so I decided against it and will go with areation. My only dilema was to submerge the stone or not. I thought the O2 would disolve in wort even if you don't shake it.
But as you pointed out there are pros to submerging the stone and I can't see any cons, so I'll probably go with that.
Thanks

 

[IslandLizard]

Yeah, I guess high krausen would be the perfec time for pitching the starter, whenever that happens.

Actually, by stirring (or shaking) while having an abundance of O2 available, the yeast remains in propagation mode, generating new cells, through budding, which is the main reason to make yeast starters: to ramp up cell count!
While in (aerobic) growing mode there's little krausen development as the yeast isn't putting all her energy into fermenting. Sure there is some fermentation taking place, but it's not the major event (or purpose).

With an unstirred jar sitting on the counter, once the O2 runs out the yeast goes into (anaerobic) fermentation mode. Sure there's some growth too, but not as much as when you keep supplying O2.

 

[Dusan Kovacevic]

Actually, by stirring (or shaking) while having an abundance of O2 available, the yeast remains in propagation mode, generating new cells, through budding, which is the main reason to make yeast starters: to ramp up cell count!
While in (aerobic) growing mode there's little krausen development as the yeast isn't putting all her energy into fermenting. Sure there is some fermentation taking place, but it's not the major event (or purpose).

With an unstirred jar sitting on the counter, once the O2 runs out the yeast goes into (anaerobic) fermentation mode. Sure there's some growth too, but not as much as when you keep supplying O2.

Yes, that makes sense. When we have high krausen yeast have already exited main propagation stage and started to ferment vigorously.
But I thought shaking/stirring is not a factor in propagation. Yeast propagate normally without any shaking when pitched to fermenter, so why it wouldn't in a starter? Only thing that makes sense is that O2 dissolves more readily when stirring.
But if you already have O2 saturated starter wort (by areatimg before pitching yeast) and then you are adding O2 on top of that, would stirring really be necessary?
From what I've read yeast doesen't need stirring to be in suspension, but stirring does help with CO2 release from wort.
Any toughts on that?

 

[IslandLizard]

I was reading, in other forums, about how continuous stiring is stressing the yeast

Yeah, yeah... there are side effects to everything.
But it's not all that stressful apparently. Look around how many brewers use stir plates and create thick layers of happy yeast that ferments wonderful beer, year in, year out.

Once you experience a few (overnight) starter blow offs on your countertop, mopping up half that good starter culture leaking all over the place the next morning, needing to start all over again each time, you'll reconsider that stir plate. Potential "shear stress" or not.
Get or build a stir plate. Or if you're that concerned about shear stress, and lucky, see if you can score a working orbital lab shaker for a sweet song.

Here are my 2 go-to sites for yeast pitch and starter calculations:
BrewUnited's Yeast Calculator
Mr. Malty

 

[IslandLizard]

if you already have O2 saturated starter wort (by areatimg before pitching yeast) and then you are adding O2 on top of that, would stirring really be necessary?

Well, O2 saturated wort is hard to come without having pure oxygen on hand. At high levels Dissolved Oxygen (DO > 40ppm?) starts to becomes toxic to yeast from what I've read. So chances are the yeast will run out of oxygen before it runs out of sugars => it will ferment the rest => CO2 production goes up => krausen => blow off => mopping.