Changes

* When propagating yeast in an Erlenmeyer flask, use a flask that allows for plenty of headspace. This allows for a thinner layer of foam and thus more oxygen diffusion. A good general rule of thumb is to use a flask that allows for 20-33% starter volume and 66-80% headspace (ideally 20% starter volume and 80% headspace). For example, for a 1L starter, use a 3L, 4L, or 5L flask (ideally 5L). More volume can be used with a Fernbach or a baffled flask, but these require a shaker table. For yeast propagation for use in beer, use wort and a magnesium and zinc nutrient, and set the stir speed to the highest setting for best yeast propagation practices. Cover the flask with foil (or [https://www.facebook.com/groups/MilkTheFunk/permalink/1034954619866085/ foam] if fruit flies are a problem) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1986378521390352/ Various MTF members. Milk The Funk Facebook thread started by Jon Stanley on Erlenmeyer flask usage for yeast starters. 02/12/2018.]</ref>.