Yeast starter - airlocks? Opinions?

I either have (made my own stir plate) or have on the way from Midwest the equipment to do a yeast starter for my next brew, which is going to be Midwest's Kolsch kit (with all the equipment making I've been doing I was feeling too lazy to put together the recipe).

I'm a little confused on using an airlock though. I thought the point of using a stir plate was to both keep the yeast suspended and also to provide aeration. If I was to use an airlock the yeast would eventually use up all the oxygen. I've seen guys on here using just aluminum foil to cover their starters for this reason. But doesn't that also put the starter at the risk of getting infected? What is everyone's opinions on use of an airlock/no airlock on a starter?

I use aluminum foil and just cover the top. I haven't had a problem yet after 8-10 starters.

I use both methods depending on time. If I know that I'm going to brew in 12-24 hours I dont use an air lock and pitch the whole starter. I cover the top with sterilized gauze. The advantage of this is that your yeast will be activily reproducing and eating the starter. When you pitch this to your wort they "hit it running" and lag time will be at a mimimum. The con of this method is that you are pitching the whole starter, which is normally made with extract....does it really matter??? probably not unless you are a pureist and you only want %100 wort in your brew.
If im not sure exactly when im going to brew (or im feeling like a purist) i will make the same starter and put an airlock on it. By doing this the yeast use up all the oxygen, reproduce and eventully fall out leving behind a larger amount of slurry. Then you can pour off the use up wort and pitch the slurry. The advantage is that you now have a good amount of yeast, but lag time will be a bit longer.
hope this helps you out
Nick

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Dunkelwiezen

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Oregon Strawberry Ale

Thanks for the info. The "purist" issue is non-existant with me considering I brew from kits and extract recipes for the time being. I don't have the equipment and especially don't have the space for all-grain. Some day...

Lol... I bought a 2000 mL Erlenmeyer flask from Midwest. At work today I looked at some in the lab. 2 L Erlenmeyer flasks are really big.... woops. I should have went with a 1000 mL. But I did learn that a credit card will buy me all kinds of neat stuff at the laboratory supply stores for my university. I was thinking that they didn't sell to the public but a fellow student told me they do sell to faculty/staff/students, they just don't sell absolute ethanol and some chemicals to the public.

There are special porous foam corks that you can use. They let air in and keep the nasties out. I just use foil.

Levers101 said:

But doesn't that also put the starter at the risk of getting infected? What is everyone's opinions on use of an airlock/no airlock on a starter?

Click to expand...

Ditch the airlock for starters. Loosely capped foil is your friend. Contaminating germs need to fall or be drafted into the flask which is not going to happen with foil on top. They don't have legs and cannot crawl or fly into your starter.

Kai

I use foil too.

Thanks guys. Yup, I agree with the nasties not being able to crawl or otherwise motate into the start. Al foil it is.

Everythinhg I have read suggests the use of foil, which I now use, instead of an airlock. My rudimentary understanding is that the yeast multiplying yeast require some 02. If you go and shove that little airlock on there, it will keep out them nasties, but also any O2.

Now how any O2 gets in a loosley foil capped vessel, while the yeast is blowing off CO2 is beyond me. I guess that's another thread all together.

I keep an airlock on my flask, but I'll give foil a shot for the O2 reason you guys mention. One fewer item to clean...nice!

My guess is that O2 can still diffuse across the CO2 layer rather easily. Gases are very good at getting into anything that isn't sealed with the utmost care. My research is all in an anoxic environment, and keeping things from coming into contact with oxygen is easier said than done. The escaping CO2 might do well enough to keep out any relatively large bacteria and nasties but then again, bacteria don't diffuse as far as I know.

While foil might not hurt in regard to keeping out germs, the o2 won't get into fermenting wort as the wort is producing co2 and co2 is heavier than o2. When growing yeast in a starter, the main goal is to grow yeast. After the initial uptake of o2 into the yeast cells the yeast grows/splits into daughter cells which then takes up o2. The process continues until the o2 is used up and then the starter begins to ferment.
Adding more food and o2 will increase your yeast count as well as keeping the yeast in suspension using a stir plate.
I use a airlock and have no trouble with my starters. I swirl as often as I can.