Two days in a row I've tried to make Pain de Mie following the recipe on this site. It calls for adding all the ingredients to a mixing bowl with yeast going in last after the flour. Both times I measured carefully and followed the instructions to the letter, but both times the dough remained flat. The yeast I'm using is the SAF purchased from this site and I've kept it in a ziplock bag in my cupboard for about a year.
Also, what is the difference between the red SAF yeast and the gold SAF yeast sold here?