[theDarkSide]

Recent scoresheets have made me wonder whether I'm aerating my wort properly.  In the past I've either shaken the carboy or used an aquarium pump/sanitary filter/stone setup.  Both methods seem to produce a lot of foam, which in turn may be affecting my head retention later.

So I ordered a O2 aeration system from Williams Brewing ( liked this one especially because of the rod that allows me to put the stone right where I want it ).  Now I want to aerate everything 

I use a stir plate for my starters, so is it necessary to aerate the starter?  Will it hurt anything if I do?  I imagine I would only need less than a minute with pure O2.

Thanks.

[jmcamerlengo]

Thats essentially what a stir plate is achieving. Are you using a stir plate? If not then yes aerate. A quick blast should do the trick. Maybe 20 seconds?

[zorch]

I use a stir plate for my starters, so is it necessary to aerate the starter?

Nope.

Will it hurt anything if I do?

Nope.

[thomasbarnes]

Recent scoresheets have made me wonder whether I'm aerating my wort properly.

What sort of feedback are you getting and what styles were you brewing?

While aerating your wort is a good thing, there might be other issues. Yeast stress doesn't just come from lack of aeration and insufficient starter - look at yeast nutrition (especially if doing beers with more than about 20% adjunct sugars), fermentation temperature (both pitching temperature and overall temp.), temperature swings and original gravity.

[mabrungard]

Unless you are pumping filtered air into the starter vessel while its on the stir plate, you aren't getting a good aeration of the wort during its growth phase.  Stirring is very good for improving the transfer of gases from the atmosphere above the wort, into the wort.  But if the atmosphere above the wort is depleted of oxygen, all the stirring in the world won't make any difference.  During active fermentation, that atmosphere will have little oxygen and a high percentage of CO2.  If an Erhlenmyer flask is used as the starter vessel, the avenue for gas transfer is restricted.  To keep contaminants out, we typically have some sort of barrier (foil, foam) over the flask mouth.  That is an impediment to gas transfer and diffusion.  An active flow of filtered air into the flask alleviates this deficiency.  There is no need to bubble the air through the wort, just exchange the atmosphere.

Enjoy!

[morticaixavier]

Unless you are pumping filtered air into the starter vessel while its on the stir plate, you aren't getting a good aeration of the wort during its growth phase.  Stirring is very good for improving the transfer of gases from the atmosphere above the wort, into the wort.  But if the atmosphere above the wort is depleted of oxygen, all the stirring in the world won't make any difference.  During active fermentation, that atmosphere will have little oxygen and a high percentage of CO2.  If an Erhlenmyer flask is used as the starter vessel, the avenue for gas transfer is restricted.  To keep contaminants out, we typically have some sort of barrier (foil, foam) over the flask mouth.  That is an impediment to gas transfer and diffusion.  An active flow of filtered air into the flask alleviates this deficiency.  There is no need to bubble the air through the wort, just exchange the atmosphere.

Enjoy!

Martin,

I have wondered about this as well. I don't use a stir plate cause I don't have one. I give it a good solid sloshing around whenever I walk by. But now I wonder, would it not be better even than a stir plate to get an aquarium pump and a sterile filter and just continously bubble air through the starter?

[mabrungard]

But now I wonder, would it not be better even than a stir plate to get an aquarium pump and a sterile filter and just continously bubble air through the starter?

It sure wouldn't hurt, but be careful with the rate and way the air is bubbled.  I struggled with this for years.  Even though I use a 6L Erhlenmyer, I was occassionally creating 'bubble-overs' if I bubbled air through the wort.  Its much worse if an air stone is used since the bubbles are much finer and frothy.  I use the same low gravity wort made from DME for all my starters.  I found that the tendency to bubble-over is a function of the yeast strain.  Hefeweizen yeasts were particularly bad for me. 

That is how I came to my current recommendation to just flood the headspace above the wort with filtered air and let the stir bar do the rest of the oxygen transfer.  No bubbling this way.  If a stirrer is not used, then I suppose that bubbling the filtered air through the wort is the way to go.  Just be sure to use a vessel that is way bigger than the amount of wort so that bubble-overs don't make it out of the vessel.  By the way, those bubbles carry a huge amount of yeast, so loosing that foam is not good for your final yeast count. 

[morticaixavier]

But now I wonder, would it not be better even than a stir plate to get an aquarium pump and a sterile filter and just continously bubble air through the starter?

It sure wouldn't hurt, but be careful with the rate and way the air is bubbled.  I struggled with this for years.  Even though I use a 6L Erhlenmyer, I was occassionally creating 'bubble-overs' if I bubbled air through the wort.  Its much worse if an air stone is used since the bubbles are much finer and frothy.  I use the same low gravity wort made from DME for all my starters.  I found that the tendency to bubble-over is a function of the yeast strain.  Hefeweizen yeasts were particularly bad for me. 

That is how I came to my current recommendation to just flood the headspace above the wort with filtered air and let the stir bar do the rest of the oxygen transfer.  No bubbling this way.  If a stirrer is not used, then I suppose that bubbling the filtered air through the wort is the way to go.  Just be sure to use a vessel that is way bigger than the amount of wort so that bubble-overs don't make it out of the vessel.  By the way, those bubbles carry a huge amount of yeast, so loosing that foam is not good for your final yeast count.

Well, it's another option. I use either a half gallon mason jar or a 1 gallon jug, depending on size. I try for 50% headspace.

[hopfenundmalz]

Unless you are pumping filtered air into the starter vessel while its on the stir plate, you aren't getting a good aeration of the wort during its growth phase.  Stirring is very good for improving the transfer of gases from the atmosphere above the wort, into the wort.  But if the atmosphere above the wort is depleted of oxygen, all the stirring in the world won't make any difference.  During active fermentation, that atmosphere will have little oxygen and a high percentage of CO2.  If an Erhlenmyer flask is used as the starter vessel, the avenue for gas transfer is restricted.  To keep contaminants out, we typically have some sort of barrier (foil, foam) over the flask mouth.  That is an impediment to gas transfer and diffusion.  An active flow of filtered air into the flask alleviates this deficiency.  There is no need to bubble the air through the wort, just exchange the atmosphere.

Enjoy!

I think I will try this.  Have all the stuff, so why not.

[Wesbrau]

I use a stir plate, but hadn't considered continuously aerating it in addition to stirring.  If I were to add continuous aeration to the stir plate, wouldn't that increase the final cell count over what I'd get from stirring alone?  If so, wouldn't that result in a higher yeast count than what Mr. Malty's calculator predicts?  Would there be a potential for over-pitching here? 

[ukolowiczd]

I use the same O2 stone aeration from Williams and I aerate my starter. Why not? O2 is O2. May as well give it a boost.

[bluesman]

I've only recently tried giving the starter wort a 30 sec shot of pure O2 then covered the flask with a loose foil and used intermittent shaking.  I always decant the spent starter wort and pitch the slurry.  This has given me good end results on a couple of batches. It's not scientific by any means but I liked the taste of the finished product.

[nateo]

Maybe Sean will chime in later. On his site (don't have a link with me) he did some comparisons of nothing vs stir plate vs O2 for starter growth. IIRC the O2 starter grew a lot more than the stir-plate starter.

FWIW I read something by a guy who graduated Weihenstephan recently, where he argued you should only aerate your starter, and pitch enough yeast so that you wouldn't have to aerate your wort at all. I thought it was interesting, but maybe only applicable to German styles with no phenolic/estery character?

[mabrungard]

The problem with a shot of Oxygen in a starter is that unlike beer, we are looking to KEEP the starter aerobic throughout the yeast's growth stage to develop a high level of sterols in the yeast.  The stoichiometric mass of oxygen to completely oxidize a sugar is about 94% of the sugar's mass.  Fortunately yeast can't fully oxidize sugars, so the oxygen demand is less than the stoichiometric value.  So that might mean to oxidize 1 gram of sugar, we might need to supply maybe 0.7 grams of oxygen.  I think we all know that oxygen is not very dense and that it takes a large volume of gaseous oxygen to provide that 0.7 grams. 

So moving a bunch of air through the headspace over a starter wort is a better way to keep a consistent oxygen supply to the wort through the yeast growth phase.  Since air is only about 21% oxygen, that means that roughly 5 times the volume of air will be needed to provide the volume of oxygen needed.  But air is cheap.  And since yeast cannot instantly utilize oxygen, a long-term delivery of a low dose better matches the yeast utilization rate. 

This does not change the fact that oxygenation is best for wort when making beer.  But for a starter and its differing oxygen requirement, continuous aeration with air is more suitable.

I agree with that comment that Nate made: if the yeast are healthy and pitched at high rate, there may not be a need for wort oxygenation when making beer.  For most of us that probably underpitch, a shot of O2 is good insurance!

[tonyp]

I'm glad i used the site search feature before asking this same question again. Great thread, thanks for the info.