Oxygen is a large part of yeast health for good reproduction.
proper oxygen levels speed the growth phase, reduces diacetyl formation, improves ability of yeast to metabolize secondary byproducts, or removes stuff that tastes bad.
do not put oil in your beer. it is not a replacement for oxygen.
the most important factors for good fermentation
1. maintain temperature, if there is more than 2 deg temperature swing between day and night it can cause yeast to go dormant. a higher temperature is better than fluctuating temperature.
2. proper pitching rate .75 billion cells / ml/plato for ale
3. proper oxygen, shaking is minimum, I use aquarium pump with filter.
also I am attaching info I have used fro propagation from single cell.
I have stopped doing this as I have found my environment is not clean enough.
of 4 attempts I found 3 to get a contamination. it only takes one cell to destroy your beer at this stage.
-Yeast_Propogation_Procedures_Complete.pdf
