Why is the Erlenmeyer style flask the automatic go to for yeast starters? I know people use other containers besides flasks, and some flasks don't have flat bottoms but is there something special about the shape or angle of the sides? Just thought this was a good question to throw out there and see what comes back!
Speaking from experience as a molecular biologist. Erlenmeyer flasks are nice for a couple of reasons. The main alternative being a standard beaker which is essentially the same size at the top and the bottom. First off the neck size makes it easy to hold in the hand. Second a smaller opening reduces the chance of getting airborne material into the flask. Third try swirling around some liquid in a normal beaker and then an Erlenmeyer flask, the narrow neck on the flask keeps the liquid inside the vessel better than a beaker. Fourth, when doing biological cultures you want to keep the media aerated and the wide bottom of the flask allows you to keep a high surface area with which to introduce air. Finally, the narrow neck allows us to use smaller stoppers which reduce the chance of contamination.
Altogether these reasons are why we use Erlenmeyer flasks in the lab.
While starters ideally don't make use of an airlock to promote maximum O2 exchange, some people prefer to use an airlock to counter wild yeasts and other contaminants. The narrow neck on the conical flask makes using a stopper and an airlock much more practical.
Alternatives to rubber stoppers are foam stoppers which permit gas exchange. Again, these would be impractical for use in a beaker or other wide-mouthed vessel, but work well in a conical flask.
There is nothing special about a flask in regard to yeast starters. Yes, t=you can boil in one, but after doing that for a while I found it more hassle than it's worth. When I used to use a stir plate, I used a gal. glass jug on it. Much less expensive for more volume. Now that I've gone to the SNS method for starters, I find the increased volume of the jug even more useful.