How can I tell if it’s ripe? See the fine bubbles on the surface and the gentle creasing? Those are good indications. I use these visuals, volume (notice it is something where I can measure the volume easily), and time to determine sourdough maturity. Some people say to see if the starter floats in cool water. I think this is a really bad way to assess ripeness— once you have significant carbon dioxide production from the yeast, it will float for some time on either side of that perfect fermentation window ledge. Don’t fall out!
These two starters have equal weight and proportion, but the one on the left is whole wheat flour. Yeast and bacteria love the added minerals that the bran in whole grain flours provide. As such, the whole wheat starter will ferment more quickly, even though the proportions, temperature and environments are identical.
I maintain a few different cultures: liquid white, rye, and sometimes stiff white. But I set whole grain starters up for specific use. They’re just too needy (as in: need to be fed more often). The magic is in the fermentation. Bran is inherently bitter— like me. When you ferment it, it becomes sweet— like me. Whole grain flours also have less capacity to trap gas, creating interesting bubbles (alveoles) and lightness in a final loaf.