I'm going to be making my first yeast starter, for a higher gravity beer.
While reading starter guides, and watching videos, I've noticed that there are several different techniques and opinions for the flask stopper. It seems that the common approach is to use a piece of sanitized aluminum foil, loosely wrapped around the top. I've seen others use airlocks, but have seen just as much on the side, recommending that they be avoided.
I bought a starter kit which included a semi-dense foam stopper (from NB). It appears that it will allow permeation of oxygen, which I understand to be important for the starter. I will soak it in sanitizer before I cap the flask.
Will this be an effective stopper? Should I skip this and go with the common aluminum foil approach?
I'm also worried about sanitization. How does the starter stay safe from infection if it's not airtight? I know it will only be exposed for a day or so, but I'm still curious about possible infection.