Breadtopia’s sourdough starter is fed organic bread flour, but you can feed it a different flour if that is your preference. This is also true of starter you’ve made yourself or that a friend gave you. Even if the starter was fed a particular flour since someone’s great-great grandma made it, the microbes will adapt: whole grain vs. refined flour, thinner vs. thicker consistency. You should continue to avoid bleached flour (less wild yeast) and self-rising flour (higher pH).
Different starters developed for recipe testing. From left to right: 100% hydration 50:50 bread flour and whole grain rye flour, low hydration whole grain durum flour, 100% hydration whole grain hard red winter wheat flour.
Breadtopia’s starter instructions recommend initially reviving the starter with all purpose or bread flour to more easily track the expansion of the starter and to have a fairly predictable feeding timeline. Refined flour forms a stronger gluten network, so the bubbles are more obviously trapped; and refined flour is consumed a little slower compared with whole grain flour. This is just a recommendation though, and it’s not difficult to monitor whole grain starter expanding in a jar and feed it a little earlier if needed. In general you should feed your sourdough starter close to when it peaks, even if this is earlier or later than when any instructions estimate. At least initially, make sure your starter has a waffle batter consistency and not thinner. Once you’re more experienced at reading your starter, you can try a more liquid starter if you prefer.
By the time you’ve done a few discards and feedings with a new type of flour, the starter will be comprised almost entirely of your new flour. This forum post by one of Breadtopia’s guest bloggers explains how changing the starter’s flour works mathematically over time. Here are a couple of recipes where the sourdough starter has been fed different flours in order to be almost 100% a specific wheat variety:
Whole Grain Spelt Ciabatta
Naturally Leavened Einkorn Bread
Here are two recipes where the sourdough starter has been made stiffer (lower hydration), and the latter recipe has sugar in the starter too, to encourage the flourishing of yeasts that will perform better in sweet dough.
Naturally Leavened Christmas Panettone
Whole Grain Sourdough Date Rolls
Finally, this article describes an experiment with feeding starter different floursand making bread with these starters and the same total flour percentages in the loaves, and this forum thread discusses flour and terroir — the regional specificity — of sourdough starters.
