Brewpastor
Beer, not rocket chemistry
Many of you have probably seen this article, but in case you have not I suggest you check it out. It is a really good source of information about yeast propagation and so forth.
http://www.maltosefalcons.com/tech/MB_Raines_Guide_to_Yeast_Culturing.php
http://www.maltosefalcons.com/tech/MB_Raines_Guide_to_Yeast_Culturing.php