Sorry, my bad for forgetting that lots of brewers oxygenate the wort. I tend not to bother and either pitch a very healthy starter or dry yeast. Having said that, I do let the wort splash around a bit when siphoning, but I’ve never bothered shaking it or using oxygen.
If I used a stir plate I could answer that by doing a test with smoke.
Liquids don’t float freely out of containers - gravity keeps them in place at the bottom of the flask. So they’re very different in this context, despite both being fluids.
Wouldn’t the smoke have to be cooled to ambient temp and weigh the same as CO2 before it started to prove anything?
Agreed.
CO2 doesn’t float freely out of a container either, it diffuses. (Assuming no outside air movement.) So yes, eventually the CO2 will diffuse out of the container, but over a period of time based on the volume, pressure, and temperature.
Food for thought: fermentation of a given volume of 10°P wort evolves about 20 volumes of CO2. Spread out over a day or two, it isn’t exactly rushing out of the starter vessel.
True but what if it’s got a pelicle?
I’d throw it out and make a new starter. :o
I was attempting to avoid this portion of the conversation because it brings back nightmares of dealing with a professor that I considered to be one step above a member of the SS. :) We are dealing with the Venturi effect when we are discussing outflow from a cone. Gas flow accelerates as it exits a cone due to the conservation of mass, but the pressure drops across the orifice. I do not see how a significant amount of O2 can move into the flask when the pressure inside the flask is higher than it is outside of the flask. According to Graham’s law, CO2 and O2 move from an area of higher pressure to an area of lower pressure.
Lower partial pressure, though. As CO2 displaces oxygen, diffusion acts to draw more in. If there’s no significant O2 in the headspace, my question is the same as before: what’s the mechanism for a starter with an airlock growing less yeast?
I wonder how a Gordon Graham graph would apply at some point
Hopefully, you are not basing your assertion on Kai’s work. A lot his work is so horribly flawed that it has me casting doubt on the accuracy of all of it.
If you’re comparing smoke in a spinning flask to smoke in a stationary flask, that doesn’t matter.
CO2 doesn’t act like a kind of invisible water, it’s much more buoyant, even if heavier than air. I reckon it would dissipate quickly if given a stir.
Sure if there"s a steady gust of wind flowing out of the flask then O2 will have a hard time flowing in but there isn’t that kind of mass flow generated by a yeast starter.
Wait, what? No, CO2 doesn’t have the mass of water. But it DOES act like an invisible water…or else it wouldn’t be a fluid. Now, have you or have you not seen CO2 being poured over a candle, like water, to extinguish the candle?
Or stuck your nose anywhere near a sink after you’ve dumped a keg in it? It takes a good while for CO2 to move, or a really strong air currant.
Along with my own, Jamil Z’s, Chris White’s, etc. The correlation seems pretty well-established, even if the mechanism is ambiguous.
Gases spread out to fill the container they occupy, whereas liquids maintain a fixed volume and are pulled down by gravity. They are different states of matter and behave in fundamentally different ways. You’re right that CO2 is a fluid, but don’t confuse that with a liquid. You can pour CO2 over a candle to extinguish it but the CO2 will spread out and dissolve in the air, whereas a liquid would fall to the floor.
But at what rate? Diffusion is not an instantaneous process. Couple that with an active CO2 source, and you have a situation quite different from that described by the ideal gas law.
If two gases are moving, they will mix very quickly, like milk being stirred into coffee. If they’re motionless then they’ll mix by diffusion only and yes that’s a lot slower. A flask on a stir plate doesn’t contain motionless gas.