Need input on American wheat ... tonight....

[rich]

That is what the stirplate does, provide continuous O2.

It also keeps the yeast in suspension, and hinders floccuation.

I aerate my starters with O2 also. I figure 100% oxygen is better than 27% oxygen. Plus I prefer to use an airlock on my flask.

[Who is John Malt?]

Plus I prefer to use an airlock on my flask.

Is an airlock necessary? Or just covering with foil/plastic wrap sufficient?

[rich]

Is an airlock necessary? Or just covering with foil/plastic wrap sufficient?

Would you trust your fermenting primary to just foil or plastic wrap? The whole foil on a flask thing was begat from the need to draw air into the vortex of a starter on a stir plate, thus oxygenating your starter, but to disallow gravity settling contaminants . If you have the gear to oxygenate via O2, why draw in nasties in an attempt to aerate?

Bacterial infection in a starter affects all of your yeast. How has general consensus allowed us to culture yeast starters in a relativley open environment, but yet we pitch this into a closed system?

Where I live I Tennessee , lactobacilli, pediocicci, and saccharomyces excidous fly about as large as sparrows. In additionm, I make cheese, sourdough bread and sauerkraut. I deal with thermophilic and mesophilic cultures and need to keep my "micro-biological petting zoo" separate.

Jamil and Dr. Scott aren't the only ones with a box of surgical gloves. I have not, as it turns out put my hands in someone elses mouth with gloves on in the name of science, but wish too.......

[Mr.Cheese]

[quote="jamilz"]That is what the stirplate does, provide continuous O2.[/quote]

How can a stirplate provide sufficient continuous O2? Assuming your solution isnt being splashed by the stirbar all it would do with the atmosphere (inside the flask) is increase the surface area. But that isnt so important because the solution is CO2 rich within a few hours and will disipate out of solution and pushing what O2 is inside the flask out.

I always though the purpose of the stirplate was to maintain a maximium amounts of nutrients across all yeast cells. It prevents yeast from sufficating eachother (from nutrients) as they fall out of solution on top of eachother. Yeast that remain on the bottom will not reproduce because they will not have sufficient O2 and nutrients.


Mr Cheese

[Mr.Cheese]

[quote="rich"][quote]Where I live I Tennessee , lactobacilli, pediocicci, and saccharomyces excidous fly about as large as sparrows. In additionm, I make cheese, sourdough bread and sauerkraut. I deal with thermophilic and mesophilic cultures and need to keep my "biological petting zoo" separate.[/quote]

I good trick that i do when adding my yeast to the starter is to turn on a bunsen burner or stove, the heat from the gas is not only sterile a good distance away from the flame but will also create an upward draft that will help keep the illegal airborn bacteria out of my starter.

Mr Cheese

[Mr.Cheese]

[quote="rich"][quote]I aerate my starters with O2 also. I figure 100% oxygen is better than 27% oxygen.[/quote]

I forgot exactly how big of a difference anaerobic vs aerobic was until i looked it up in my old school books. The longer you can remain in aerobic (o2 using) the better.

Aerobic respiration: C6H1206 + 6 O2 => 6 H20 + 6 CO2
Anaerobic respiration: C6H1206 => 2 C2H5OH + 2 CO2

Aerobic will produce up to 36 ATP molecules vs 2 in anaerobic per glucose molecule! ATP is used by most biochemical reacctions in cells. So thats up to 18 times more power. If i remember right, the effects of budding are also far less since cells can then spend extra engergy and more time in S0 reparing themselves.

Mr Cheese

[Speyedr]

That is what the stirplate does, provide continuous O2.

How can a stirplate provide sufficient continuous O2? Assuming your solution isnt being splashed by the stirbar all it would do with the atmosphere (inside the flask) is increase the surface area. But that isnt so important because the solution is CO2 rich within a few hours and will disipate out of solution and pushing what O2 is inside the flask out.

I always though the purpose of the stirplate was to maintain a maximium amounts of nutrients across all yeast cells. It prevents yeast from sufficating eachother (from nutrients) as they fall out of solution on top of eachother. Yeast that remain on the bottom will not reproduce because they will not have sufficient O2 and nutrients.


Mr Cheese

The stirplate definitely does what you say above, but the whirlpool created in the flask also draws the "air" into the wort continuously, providing O2 to the yeast.

As for the foil cover on the flask, it's just fine (unless you have an O2 system) since all you are doing is providing the yeast with a better starting point than the nasties. If you start with a tube of yeast and pitch it into a starter on a stirplate, they will quickly outnumber the nasties by a HUGE amount and they'll use up the nutrients before the nasties can even get started. This is why we can do open PRIMARY fermentations if we want, say in a Belgian "Inspired" beer. This is also why we only have to sanitize and not sterilize unless working with small cultures.

As I understand it, closing the system during fermentation helps because you want the yeast to eventually use up the O2 and switch from an aerobic cycle to the fermentation cycle to create the alcohol. Given a choice yeast would "prefer" to feed off of O2. The absence of O2 kicks them off into fermentation for survival. So if you close your starter flask with an airlock and don't provide another source of O2 the yeast will eventually stop growing and start fermenting once the O2 runs out. This happens much more quickly without a stirplate, which is why you would get 4x the amount of yeast when you use a stirplate.

The sick thing is that this makes sense to me now as opposed to a month ago..

[Mr.Cheese]

[quote="Speyedr"]The stirplate definitely does what you say above, but the whirlpool created in the flask also draws the "air" into the wort continuously, providing O2 to the yeast.
...
source of O2 the yeast will eventually stop growing and start fermenting once the O2 runs out.[/quote]

Back when (when was a while ago) i was in a lab, that was a no-no. Excessive motion causes stress on the yeast cell walls and ruptures. The ideal speed was just fast enough to keep the yeast from settleing out. This would be a real good interview question for the white lab folks.

I think your right. Most worts are aerated so you wouldnt want your yeast to have to switch back to aerobic when they are pitched. This is why i have been measuring the decrease in weight of my starters. Thats interesting though because if you could pitch the amount of yeast your wort requires, then you can pitch anaerobic yeast in a low O2 wort. How well would that work?

Mr Cheese