Stirplate questions.

[rferguson61]

I've been thinking about making a stirplate but there have been two major concerns in my mind. First is it sanitary? I see everyone doing there's with an open top. Doesn't this allow for contaminants to get in? Second...does the spinning of the bar on the beaker wear away the glass and mix glass powder in with the yeast? Thanks!

 

[dmfa200]

One would want to cover the mouth of the flask with aluminum foil to keep bacteria and wild yeast from getting to your starter, and also allow for an exchange of Oxygen in and CO2 out.
As far as the stir bar.
A good quality stir bar is coated with Teflon. It will not wear on the glass. They can also be boiled and sanitized along with the starter, and will not melt.

 

[rferguson61]

Would a rubber stopper with an airlock be a good way to seal it and allow for the exchange?

 

[dmfa200]

The airlock will allow for the release of the CO2, but makes it difficult for Oxygen to enter.
Oxygen it what the yeast need to help them replicate.
Aluminum foil works just fine for the exchange of O2 and CO2, and also keep out the nasties.

All you have to do is wrap the foil over the mouth of the opening firmly, and that's it.
You don't have to secure it with anything. It will stay in place on it's own.

 

[smokinghole]

You can do aluminum foil or a foam stopper that allows oxygen to pass through. You want O2 to get in. You can even just leave nothing on the top as long as your confident in the cleanliness of the location you set the stirplate. Remember there are still breweries that use open fermentors and this is less than a 3" diameter hole. They're dealing with a few feet of wort exposed.