kdsarch

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So I made a yeast starter in a 2l flask from harvested yeast this past weekend.

The recycled yeast was Wyeast London Ale. The equipment was a 2L flask with a double bubble airlock and #10 stopper. No stir plate.

This produced a fair amount of yeast in two days, but i noticed when i swirled the flask, a lot of bubbles went through the airlock, but none at other times when it was just sitting there. I see a stirplate in my future, but I don't have one just now.

So, do most people use an airlock on their flasks? It would seem that this might inhibit yeast growth somewhat. If there is no stir plate, would it be okay to leave the top open with perhaps a foil cover to let some air out and promote yeast growth? Also, since I don't have a stir plate to promote faster growth, should I plan on 2-3 days for the starter to produce enough yeast?

BrewDey

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My understanding is that the wort in a starter can be just as fragile and susceptible to infection-so I always use an airlock. I don't think that it really inhibits yeast growth because I aerate the wort as well.

T-Hops

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I never use an air lock on my starters. A piece of tin foil or a foam stopper is adequate.

dehn0045

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my understanding is that using a stir plate for a starter accomplishes two main goals:

1.) Keeps yeast in suspension -- which keeps the yeast busy rather than allowing them to settle and get lazy.

2.) Helps drive off CO2 and promotes oxygenation.

The only way to achieve oxygenation would be without an airlock. If you use an airlock you would create a pure CO2 headspace in the flask. From my reading, you wouldn't hurt your yeast by using an airlock but then again you aren't giving the yeast the best chance to reproduce and live fat and happy. The end result would be a lower total cell count and possibly somewhat less healthy yeast.

The argument about infection is valid, however, remember that wild yeast and bacteria cannot travel long distances. In the world of single celled organisms the 10 inch travel from the table to the lip of the flask would be like walking from here to Mars. Most experts recommend using sanitized foil wrapped around the top of the flask, loose enough to allow a small amound of air exchange. Some also recommend using a fowm stopper. Very few experts (at least in my research) recommend using an air lock.

So, get a stir plate, but don't use an air lock. If you still want to use an air lock, don't bother getting a stir plate.

Check out mrmalty.com for what I think is some pretty good advice on this topic. Also check out the HBT threads on making your own stir plate -- you can make your own for a fraction of the cost...

fratermus

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Or pour into a new container and aerate when stepping up, or introduce aerated wort when stepping up. Or continuously inject oxygen.

I am agnostic about the theory that foilcapping allows signifcant oxygen introduction, given the heaviness and positive generated pressure of CO2. It would be interesting to see if anyone had measured 02 levels in foilcapped v. airlocked spun liquids. I am open to reading evidence from testing, and open to following whatever works best.

I do use the foilcap technique frequently because I cap my flasks with foil when sterilizing them in the pressure canner, but not because I think I am getting any meaninful air exchange.

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