Erlenmeyer vs. Growler

[Pentaquark]

I have a question about oxygenation levels of yeast starters and their dependency of the containing vessel.

Specifically, I have a stir plate at home that I use for my yeast starters. I have a 1 L flask that is turning out to be too small for what I'm growing in to. The next step up would be a 2 L flask. But, alas, I am cheap. And I happened to notice that a 2 Qt growler is approx. the same volume as a 2 L flask, is half the price, and generally comes filled with beer first. However, I borrowed one to test how it worked and noticed several things: I cannot spin up the mag bar to high levels (~100 rpm or so) due to the concave bottom and then non-angled sides don't really allow for a very large vortex in the center.

Without this vortex and subsequent mixing and larger surface area, I'm concerned about the oxygenation levels of the starter culture and therefore the overall health of the yeast I'm producing. Have any of you read anything on this? I'm guessing they will grow the same number of cells but, being in a less oxygenated environment, produce less healthy cells.

Has anyone thought/read/been lectured to about this topic?

[Matt]

Just keeping your stir-bar spinning for any reliable length of time on that concave growler bottom is going to be reason enough to buy a proper flask. My two cents.

Matt

[Frank]

I cannot spin up the mag bar to high levels (~100 rpm or so) due to the concave bottom and then non-angled sides don't really allow for a very large vortex in the center.

From everything I have been told/read you're not actually going for a vortex. A depression on the top of the spinning wort is more what you're after. While appropriate oxygenation is necessary it's not all that going on here. I believe the most beneficial thing you're doing by using a stir plate is keeping the solution of yeast, sugar, water, and oxygen it constant motion creating a near perfectly disbursed overall solution.

Everything (Water, alcohol, yeast, sugar) has a slightly different destiny and as such there is some amount of stratification going on here. Also the yeast (during fermentation) are staying afloat in suspension mainly because of their biological processes. As witnessed by the fact that they "flocculate" (fall out of suspension) after fermentation when they enter the dormant phase, but are not dead because they become active again if given more sugar.

Finally if you're having a hard time out growing a 1L flask, I would stick with a growler until you have saved money for a 5L flask. This should get you all the way up to 15 gallon batches.

http://www.amazon.com/gp/product/B0021H ... 00_s00_i00

[JMcG]

I hear a barbell shaped stir bar will work with a growler.
You don't need a whirlpool, just keep the solution circulating to provide O2 to the yeast.
jim

[Rob Martin]

So....who wants to hunt out a bulk buy of 5L flasks?

[Matt]

If the price was right, I'd take some of that action.

[Pentaquark]

I believe the most beneficial thing you're doing by using a stir plate is keeping the solution of yeast, sugar, water, and oxygen it constant motion creating a near perfectly disbursed overall solution.

Everything (Water, alcohol, yeast, sugar) has a slightly different destiny and as such there is some amount of stratification going on here. Also the yeast (during fermentation) are staying afloat in suspension mainly because of their biological processes. As witnessed by the fact that they "flocculate" (fall out of suspension) after fermentation when they enter the dormant phase, but are not dead because they become active again if given more sugar.
http://www.amazon.com/gp/product/B0021H ... 00_s00_i00

While I agree that placing everything in suspension speeds the process and allows isotropic conditions for the yeast to grow, I am in the camp that it is the oxygenation of the mixture is the more important part. The CO2/O2 exchange is generally the limiting factor in healthy yeast growth, e.g. plenty of 02 for cell wall production and no CO2 mucking up chemical potentials. I work in a biophysics lab and when biochemists produce their yeast, they're shaking entire 5L flasks at several hundred rpm. This things are really being thrashed and it's entirely to facilitate the CO2/O2 exchange.

Hence my original question, whether or not growlers are providing enough O2 for the yeast and whether or not a reduced amount of surface area and turbulence was providing the same amount of aeration as the high surface area/high turbulence of a flask. What I'm guessing this all boils down to is that I'm way over thinking this and I should just sit down, shut up, and use a growler so I don't have foam everywhere.

[kevputo]

when biochemists produce their yeast, they're shaking entire 5L flasks at several hundred rpm.

I'm intrigued by this. Do you mean they put the 5L flasks into something like a paint shaker, or some kind of wobble plate? I've had "build a stir plate" on my list of DIY projects for awhile. It's stayed toward the bottom of the list for awhile, in part because I knew I'd need to spend more on flasks & stir bars than the plate itself. So up to this point I've just used growlers & manual shaking whenever I make a yeast starter.

Now you've got me thinking maybe a homemade shaker plate would be about as easy to build, and would allow me to keep using growlers or other cheap vessels. And as I type this, I'm feeling really dumb for not thinking of buckling a growler into my daughter's baby swing for my last starter.

[overdrive]

And as I type this, I'm feeling really dumb for not thinking of buckling a growler into my daughter's baby swing for my last starter.

lol - even better: babies are always being coddled, carried, bounced, rolled around, etc. Just strap the starter to your daughter!

[Pentaquark]

So what I'm talking about are called 'laboratory shakers' and they look like this. Our lab uses 6 4 L flasks at a time and then cranks it to 260-300 RPM depending on if we're growing yeast or E. Coli.

[JMcG]

Cranking the stir plate up can cause some problems. Just be sure that it doesn't heat up the wort too much and doesn't "throw" the bar (then you have no gas exchange).
The volume of wort and size of the inoculate are the key to how much growth you get, higher O2 will get faster growth, and healthier cells if the wort is proper gravity and temp. How much faster? I'm not sure you'd be able to tell much difference between a big whirlpool and a little one.
Chris White and Jamil Z (in Yeast) say a whirlpool isn't required.
jim

[Pentaquark]

Thanks Jim. I read that book from the library a while back but couldn't remember what it said. I really should buy it sometime.