724b

Recipes 

If you are using an airlock, that could be a problem.

If you're using foil or a foam stopper, which is recommended, I think that there is airflow because of the liquid movement.

kanzimonson

Recipes 

People believe that because CO2 is denser than air it forms a distinct layer, but this is just not true. There's CO2 in air... it moves around and gets incorporated.

CO2 and air are not oil and water, they're honey and maple syrup - eventually they mix.

Pivovar_Koucky

Recipes 

Yes, but they mix by diffusion or by convection. If you have 1 liter of wort at 20 degrees C (68 F) and the gravity goes from 1.040 to 1.010 then you make 16.67 L of CO2. If that takes 48 hours then you're talking 347.3 cubic centimeters per hour. Unless O2 can diffuse against that flow rate, CO2 will quickly push all of the O2 out of the flask.

kanzimonson

Recipes 

I'm curious if there's a correlation between the way liquid moves in the starter and the way gas moves in and out of the flask.

What I mean is, the whirlpool of the starter creates a lower pressure region in the center of the flask. Does that mean that more CO2 is leaving the center of the starter, in general? Or do you think this is a negligible effect? If it's true, perhaps more O2 is able to enter the liquid at the edge of the surface?

Just throwin out some pseudo-science here...

Pivovar_Koucky

Recipes 

I'll tell you what, someone measure the internal diameter of the mouth of a 1L erlenmeyer flask and give me some ballpark numbers for their starting and ending gravities and the time it takes to ferment and I'll crunch the numbers and come back and post my results.

kanzimonson

Recipes 

My 2L flask (which I'm guessing is the size that most people use) is 1-5/8 (1.626") in diameter at the mouth. To be clear, this is not including the thickness of the glass.

Pivovar_Koucky

Recipes 

I don't think that the whirlpool is due to lower pressure, it's due to the fluid flow being constrained at the walls. If anything I would expect that less CO2 is leaving at the center than at the edge because the height of the fluid column is less there, so less yeast is farting out CO2.

kanzimonson

Recipes 

Maybe I've got it wrong, but I thought I've heard it explained that the lower pressure is due to the whirlpool. Because of the constraint at the walls, the highest pressure is at the edge of the flask. The lowest pressure is in the dead center of the tornado. Fluid moves from the tornado, out to the wall, down to the bottom along the wall, towards the tornado along the bottom, and then up to the top of the flask through the tornado.

Pivovar_Koucky

Recipes 

Would you say you usually fill the flask up all the way to the 2L mark or is it more like 1.5L?

724b

Recipes 

Interesting. That's a lot of gas!

It is constantly degassing co2, right? When it degasses, something needs to flush back in to take it's place. Otherwise it would create a vacuum.

If a bottled beer absorbs oxygen through a crown cap (which is does). Surely oxygen flushes back into a starter through foam or aluminimum foil. Right?

I feel like there is enough movement to cause gas movement in and out of the starter.

Are feelings part of science?