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Old 03-23-2011, 12:37 PM   #21
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Originally Posted by BoundForBeer View Post
But when it is fermenting it produces co2 which would push the o2 out of the container...the co2 blankets the wort
I would think the motion of the spinning liquid would disrupt that "blanket" of CO2. See the response to the next quote below:

Originally Posted by kanzimonson View Post
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.
Bear with me, I know it's wikipedia, but it's pretty straight forward:
Wind is caused by differences in pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure. On a rotating planet the air will be deflected by the Coriolis effect, except exactly on the equator. Globally, the two major driving factors of large scale winds (the atmospheric circulation) are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces) and the rotation of the planet.
The circular motion of the liquid created by the stir bar and resulting vortex, and the friction of the movement between the air and surface of the liquid should definitely create at least a "starter-sized" breeze in the flask/jug/whatever.

I have a 12 month old who always ends up with bits of food/snacks on the floor around her high chair. I picked up a couple pieces of some snack she was eating that floats in water and put them in a flask of water and put it on the stir plate to see how they moved around. They all spun on the surface until being drawn into the vortex and then were kicked out of the vortex by being batted by the stir bar or simply tossed because of the centrifugal force. Sometimes they went all the way out to the outside wall and up to the surface to repeat and other times they were drawn back into the vortex by the flow of the liquid.

I know, it's based on floating pieces of food and not yeast cells, but it demonstrated a flow even better once the pieces got a little soggy and started breaking apart.

Originally Posted by gtheroux View Post
When there is oxygen present the yeast multiple, not ferment... the reason the stir plat is so effective is that when it is stirring they just have sex... no eating the sugars at this point... hump hump hump all night long... and then when you stop there are crazy amounts of yeast who only then start fermenting... To my understanding, this is why the stir plate is so effective

Who has starters fermenting with in 24hrs anyways?
I would think the vortex spinning in a manner to draw liquid, objects, air, etc down into it would create a vacuum in the flask and thus draw air from outside the flask into it. Add onto that the potential of CO2 created by the yeast if there is fermentation or gases created by their reproduction and I would think it would cycle just fine.

All I can say is after pitching my first batch of yeast from a stir plate on Saturday, I had a layer of thin krausen covering the entire surface of the wort in under 5 hours. Not just air lock activity, but a surface of foam. I had 3-4" of krausen and vigorous fermentation in under 12 hours. I don't think I've had that even with dry yeast.

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