A few questions and comments about starter cultures

[peanutaxis]

So I decided to start making starter cultures.

I built a stirrer out of a computer fan. I am assuming that the reason for using a stirrer, as opposed to just letting it sit stagnant, is so that the yeast has plenty of oxygen to multiply, yes?

Anyway, after a few hours my starter culture grew a foam on top. Now, it occurs to me that this foam is bubbles of C02, and since the foam covers the entire top of my culture, it is now starved of oxygen again Do people worry about this?



thanks,
p

[Soldat Louis]

...


Well, we wouldn't want that, would we ?

[rubber duck]

Nope it's just fine.

[peanutaxis]

In the end I simply placed the stirrer on the side of the glass that contained my culture. This ensured that some liquid was being exposed to the atmosphere.


cheers,
p

[peanutaxis]

Can anyone confirm why a starter culture needs to be stirred?

[Washashore]

To oxygenate the starter for cell reproduction and growth.

[myles]

To be honest with you I oxygenate the starter culture by agitation when I add the yeast, but thereafter I just leave it alone. Provide you start with about 1/2 the concentration of sugar in the starter as compared to the main wash, it should get away fine.

My usual routine is to mix up my wash, take off a pint and put that in a gallon demijon to which I add a pint of water and pitch the yeast. Over the next day or 2 (dependent on ambient temperatures) I will gradually add more wash until I have about 6 pints going strongly, and then I dump that all into the fermenter. A 1 gallon starter works for me up to about 20 gallons of wash.