Stir-Plate question

[Cregar]

Hey all,

Just finished building my stir-plate and have a question.

I notice when the vortex (???) actually comes down and hits the stir rod it bubbles up. Is that ok??

I have uploaded a video on Youtube but I don't think it shows the bubbles that well. (excuse the cough).

 

[BrewMoreBeers]

i don't know, but would like to.

 

[Catt22]

Slow that puppy down, if you can, that is! You don't want or need a vortex and especially one that reaches all the way down to the stir bar. A vortex that deep is usually very noisy and it can actually interfere with the stir bar to the point it will get thrown. A gentle stirring action is more than sufficient.

 

[BrewBeemer]

Shaken but not stirred, "Bond".
A vortex 1" deep is plenty with water even less
stirring thick yeast I have found as plenty.

Catt, your up late again, waiting for "The Tonight Show with Jay Leno"?
I'll wait for his jokes then hit the sack.
Were in for a week of heavy rain with flooding possibly,
"bad day to be a bum" pops would say.

 

[Catt22]

Just got home from the last night of Beermas. It's a tradition our club has of meeting at a different bar/restaurant on thirteen week nights just prior to Christmas. I'm never able to attend every night, but I try to make it to at least half of them. Stone IPA on tap was a nice treat this evening.

I find it very difficult to have pity on residents of the golden state. A little rain and already you are cry'in. Jesus!

 

[BrewBeemer]

Jesus!

That's me but only on Sundays.
I hate rain spent too many years working outdoors year round sweating in rain gear flat sucks.
If it would rain heavy and be done is fine it's that damn drizzle for days producing no useful amount flat sucks.
Take Oregon off my list, green and pretty for a reason.

 

[Cregar]

Cool.... thanks guys, that's what I thought it was but wanted to double check. The fan I'm using is the type with the three speed settings, I might need to cut that off and attach one of those rheostat (???) for better speed control.

Thanks again for the help

 

[Henrythe9th]

The whole point of a stir plate is to interduece O2 into the wort, so yes you want a good deep vortex, when the bubbles hit the bar, oxygen gets dissolved into the wort
my understanding

 

[lowlife]

Looks fine to me. If it doesnt throw the bar I dont see a problem.

 

[BrewBeemer]

Continually pulling the surface exposing it to air for a constant surface change by stirring action is all that is required for adding oxygen from the air to your yeast. A vortex inducing air is not required unless you like throwing the magnet with having dizzy yeast is your thing.
Why not use a blender then, really add some air or oxygen to the yeast?

 

[Bigscience]

The whole point of a stir plate is to interduece O2 into the wort, so yes you want a good deep vortex, when the bubbles hit the bar, oxygen gets dissolved into the wort
my understanding

I'd say that driving off the CO2 and keeping the yeast in suspension is the true benefit. Besides, if you have CO2 filling the head space and pushing out after fermentation starts, where is the O2 coming from? The CO2 in solution is inhibiting the yeast growth. I run my stir plate slow enough to just cause a slight "inny". Going too fast can actually put too much force on the yeast an do damage. I can't recall the exact number but I want to say it was ~120 rpm being about the max that you'd want to go.

 

[ClaudiusB]

I'd say that driving off the CO2 and keeping the yeast in suspension is the true benefit. where is the O2 coming from?

In my case, air pump.


Cheers,
ClaudiusB

 

[Catt22]

I'd say that driving off the CO2 and keeping the yeast in suspension is the true benefit. Besides, if you have CO2 filling the head space and pushing out after fermentation starts, where is the O2 coming from? The CO2 in solution is inhibiting the yeast growth. I run my stir plate slow enough to just cause a slight "inny". Going too fast can actually put too much force on the yeast an do damage. I can't recall the exact number but I want to say it was ~120 rpm being about the max that you'd want to go.

The gas exchange occurs at the surface of the wort. ie, CO2 out and O2 in. So long as the flask is vented to the atmosphere, O2 will infiltrate the wort and CO2 will exit. The CO2 exiting the flask does not prevent O2 from entering. See Dalton's Law of Partial Pressures (Henry's Law too) for a detailed scientific explanation of this phenomenon. A review of the Ideal Gas Law would also help I'm sure. Stirring moves wort to the surface which is where the action is. The rate that the CO2 leaves and O2 enters the wort is a function of the degree of saturation. IOW, if the yeast is producing CO2 faster, it will exit faster and the same for the incoming O2 as it is consumed by the yeast. The two gases are pretty much oblivious to each other when passing in and out of the solution. Stirring very fast and drawing down a deep vortex won't do much other than create a lot of noise and bubbles vs a moderate stir rate.

 

[Cregar]

Thanks again for all the info Im going to try it at a slower speed setting.

 

[Waunabeer]

How long should you leave it on a stir plate? I've had mine on it for abut 24 hrs. Is that too much, not enough, what? I cannot find a discussion anywhere that states a time frame.

 

[Catt22]

How long should you leave it on a stir plate? I've had mine on it for abut 24 hrs. Is that too much, not enough, what? I cannot find a discussion anywhere that states a time frame.

IMO, the time frame is not at all critical. Most starters will finish out in 24-48 hours and much depends on the ambient temperature. My typical 2 liter starters usually finish out in about 24 hours at 75F or so. It does no harm to leave the starter on the stir plate longer, but also very little to gain. A good way to tell if it's finished out is to stop stirring and examine the wort closely right near the surface. A flashlight or other bright light helps a lot with this. CO2 bubbles rising to the surface indicate that there is still some action going on. If the wort is essentially still, it's finished.