Beer Forum

Guys,

If a stir plate grows more yeast in a given starter volume, because of increased oxygenation and physical agitation of the culture, would a system that stirs the culture BY constantly oxygenating it work just as well.

I am thinking an aquarium air pump and a plastic tube with holes in it at the bottom of your culture jar. Air goes in, bubles rise to the surface agitating the culture and dissolving some of thier O2 into solution.

Does this not achieve all the things a stir plate does? and no mucking about with fans and magnets. plus a fair few homebrewers already have air pumps. Heres the sort of thing I mean



Or is there a point where the sample would become too oxygenated? and if so, why doesn't that happen with a stir plate?

Opinions anybody? Jamil?

I also had this idea already and I think it will work well. I have read about commercial yeast propagators build that way.

One thing to keep in mind is that there will be a lot of foaming if you constantly aerate the wort. So design for lots of head space or add a tiny amount of oil. You should also make sure that you don't bubble to much air into the yeast. To much can be bad and cause the yeast to age faster. So use just enough to keep them in suspension. Maybe the air should even cycle on and off periodically. One guy on a German home brewing board even uses an aquarium pump and a stir plate to grow large amounts of yeast.

I just don't have an aquarium pump and air filter yet to go this route

Kai

It doesn't produce as much yeast as the stir plate. I believe it is because it doesn't quite suspend the yeast like the stir plate and doesn't drive off the CO2 as effectively.

As Kai mentions, the foaming can be a big problem and you can also evaporate a large amount of the liquid if you're not careful.

What I find interesting is shaking the starter (put it in a 2 liter PET bottle or a Nalgene type container) produces nearly the same amount of yeast as a stir plate if you keep on top of it. And it just as or more effective than bubbling air through the starter.

jamilz wrote:It doesn't produce as much yeast as the stir plate. I believe it is because it doesn't quite suspend the yeast like the stir plate and doesn't drive off the CO2 as effectively.

The commercial design that I had in mind has a perforated plate at the bottom, from which the air enters the propagation medium (b/c I don't want to call it beer) very evenly. This keeps the yeast in suspension. Maybe I'll need to find that link again.

But building such a propagator for HB use would be more complicated than building a stir plate.

Kai

So there you go.

I assumed that other people had thought of this and tried it. So it works, but not as well as a stir plate then. OK.

I did think about foaming and thought that to keep the yeast in suspension you might need to have the airflow up so high it would fob over.

Jamil, do you think that perhaps the reason that a shaken up PET bottle works nearly as well as a stir plate, is because the air inside the erlenmeyer on a stir plate is not being refreshed (assuming that the flask is airlocked or covered in foil), but when you release the pressure in a PET bottle, it gets a bit of squeezing and new, fresh oxygen rich air is pulled into the bottle before you shake it?

Graham Sanders specifically suggests using PET bottles for starters, and giving them a "squeeze" to renew the air before you shake them every hour or two. Thats probably how I will do my starters till I get around to building a stirplate.

I believe that Doc said that he uses an airstone IN his sitrplate flask; and Kai said he knows of a german homebrewer who does too... Does it make a significant difference to the volume of yeast you are able to grow on the stirplate Doc?

Thanks for the feedback

Thirsty

PS: Why do people freak out about airborn bugs and using Heffa (Heppa, Hepha??) filters on aquarium pumps, but no one seems all that worried by shaking the crap out of a fermentor and whatever bugs that might be in the air getting mixed into the wort that way? Not critisising anyone, just wondering

Thirsty Boy wrote:PS: Why do people freak out about airborn bugs and using Heffa (Heppa, Hepha??) filters on aquarium pumps, but no one seems all that worried by shaking the crap out of a fermentor and whatever bugs that might be in the air getting mixed into the wort that way? Not critisising anyone, just wondering

I believe it is not just airborne bugs but also the oil used to lubricate the air pumps that people are worried about. That stuff doesn't taste good...

Thirsty Boy wrote:PS: Why do people freak out about airborn bugs and using Heffa (Heppa, Hepha??) filters on aquarium pumps, but no one seems all that worried by shaking the crap out of a fermentor and whatever bugs that might be in the air getting mixed into the wort that way? Not critisising anyone, just wondering

That's why I don't like the method of getting O2 into the wort though shaking it in air. Neither for startes nor for the wort.

In general, you will be able to move much more air though the wort with an aquarium pump than you can with shaking. Thus the exposure to contaminants will be higher.

Kai

I finally won a bid for a stir plate on ebay. Jamil, should starters be made at the target temperature of the fermentation? I would think so, but the yeast companies do not address this issue. Perhaps beacuse they advertise their products as pitchable, not needing a starter. Also, do you put a pellet or 2 of hops into the starter, so as to give it a very similar media as the wort?