hES media has a two week shelf life. hES cells should be cultured in 4, 6, 24, 48, 96 well plates. Growing cells in flasks is not recommended because it is very difficult to scrape cells in flasks. hES cells need to be fed everyday with hES media. You can add 2 volumes of media and then not feed for 48 hours (ie. over the weekend.) You should pick differentiated cells off of the plate if more than 5% of your culture is differentiated. Alternatively, you can pick to keep the good colonies if there is massive differentiation within your culture.