stratslinger
Well-Known Member
Well, I'm kind of embarassed to be asking this, considering I've been using one for over a year now, but I've recently read (and been given) a few pieces of conflicting advice regarding stir plates, and I'd like to get a real understanding here. I've heard at least three different purposes for stir plates, with a few counterpoints, and a couple cases where those purposes appear to run counter to one another. I'll outline those here:
1) The stirplate is meant to constantly aerate the starter, drawing in more oxygen to keep the yeast in the aerobic stage of their lifecycle. On first blush, this is the purpose I had assumed was the actual purpose of a stirplate. However, on reflection, isn't the yeast, even in this phase, still constantly giving off CO2? If the starter is off-gassing CO2, creating a sort of positive pressure, is it even going to be possible for it to then draw in any "fresh" O2? So I'm beginning to question this as a purpose.
2) The stirplate is meant to "drive off" CO2. I've read this one several times recently, and it just seems silly to me. We've all looked at the airlock on our fermenter once fermentation is under way, and seen them bubbling away furiously, so it's pretty clear that the CO2 drives itself off on its own. I'm pretty sure this one can be dismissed out of hand. And in this case, the driving off CO2 seems to run directly counter to drawing air into or aerating the starter...
3) The stirplate is meant only to keep the yeast from floculating in the starter, so they'll stay active and reproducing. This one makes a little more sense to me, but then if this is the case it doesn't seem to jive with the general advice to not put an airlock on a starter, but to instead use a foam stopper or simply a piece of sanitized foil...
My main reason for trying to understand this is to try to figure out if I'm running my stirplate too fast, or not fast enough, or, hopefully, just right. I'm hoping for some answers backed up with some sources I can do some follow-up reading on my own.
1) The stirplate is meant to constantly aerate the starter, drawing in more oxygen to keep the yeast in the aerobic stage of their lifecycle. On first blush, this is the purpose I had assumed was the actual purpose of a stirplate. However, on reflection, isn't the yeast, even in this phase, still constantly giving off CO2? If the starter is off-gassing CO2, creating a sort of positive pressure, is it even going to be possible for it to then draw in any "fresh" O2? So I'm beginning to question this as a purpose.
2) The stirplate is meant to "drive off" CO2. I've read this one several times recently, and it just seems silly to me. We've all looked at the airlock on our fermenter once fermentation is under way, and seen them bubbling away furiously, so it's pretty clear that the CO2 drives itself off on its own. I'm pretty sure this one can be dismissed out of hand. And in this case, the driving off CO2 seems to run directly counter to drawing air into or aerating the starter...
3) The stirplate is meant only to keep the yeast from floculating in the starter, so they'll stay active and reproducing. This one makes a little more sense to me, but then if this is the case it doesn't seem to jive with the general advice to not put an airlock on a starter, but to instead use a foam stopper or simply a piece of sanitized foil...
My main reason for trying to understand this is to try to figure out if I'm running my stirplate too fast, or not fast enough, or, hopefully, just right. I'm hoping for some answers backed up with some sources I can do some follow-up reading on my own.