Add unbleached flour of choice to a mason jar (my favorite are these weck jars though!).
Add spring water (you don’t want filtered, you really do want the added minerals) until the dough resembles a thick pancake batter (don’t go too thick, or your starter might struggle to get started)(and don’t go to liquid-y as you might end up creating something unintended). If you’re using something like King Arthur’s bread flour (which is the only unbleached flour in the “popular marketplace” I recommend for sourdough), generally a 1:1 ratio of flour to water is enough to get the consistency right. But if you’re using heritage grains or most gluten free flours you’ll need to add a little more. Remember: thick pancake batter
Allow to rest for 24 hours in a warm(ish) place: I just keep it on top of my gas stove (your oven with the light on is a classic choice too).
discard (and feed) your starter
Discard half (like just eye ball half your starter and throw it out- don’t overthink it). And repeat the process of adding 50g of flour and 50g spring water (or just enough water until you get a nick thick, but mixable, consistency).
Keep going for at least 7 days… but in my experience it’s more in the likes of 10-14 to build a strong culture (but you should be able to bake a nice loaf in a week).
p.s. feel free to dothe burn test: once it is doubling in size consistently, tap your starter on the counter to “break the surface”, light a match and if it blows out it means your starter is using up all the oxygen in the surrounding area (i.e. its ready and it’s sourdough time!)(see video).
Video
Notes
*please note that all sourdough recipes on the site are developed around King Arthur's Organic Bread Flour (for consistency sake)(and because its my personal favorite "generic" flour to bake sourdough with)(but I generally also test all the recipes with other heirloom & heritage flours– Hayden Flour Mills makes some of my favorite blends). that said, please note that adding a touch of rye to your sourdough starter is a fantastic idea ;)