Hey everyone.  I've got some experience baking bread in the industry, but am struggling with my at-home sourdoughs.  I started a 100% hydration sourdough (by weight, of course) a week ago with unbleached white flour, and have been feeding it regularly ever since.  The starter clearly has activity: it smells very sour at the end of a 12 hour period and has plenty of gas production (bubbles are seen at the surface), but I'm not seeing any rising of the starter.  I know a lot of people say starters are ready to use after they double in a 12-hour period, so I'm beginning to wonder if I made a misstep somewhere.  Any suggestions?