Sourdough

Hello, my name is Gaye and I have been making sourdough bread successfully for many years now.  However, I am still keen to learn more about the science.  A couple of questions please.  In your video you say the following: 

 "Once your starter can pass the "float test" 12 hours after feeding, it is strong enough to bake with. At this point, you can either bake your first loaf of sourdough bread or retard in your refrigerator, remembering to feed your new starter at least once a week."