I thought I’d add my thoughts on making sourdough when you have no yeast.
Get a 1 or 2 quart glass bowl….one that you won’t be needing for a while. Put in 1 cup (113g) of whole wheat flour (all purpose is also fine) and 1/2 cup (113g) cool water. Stir and then cover with cling film. Leave on the counter in a cool place. That’s day 1!

Day 2: You may see no activity at all in the first 24 hours, or you may see a bit of growth or bubbling. All the recipes will tell you to discard half the starter (4 ounces, about 1/2 cup), and add to the remainder a scant 1 cup flour, and 1/2 cup cool water (if your house is warm); or lukewarm water (if it’s cold). I hate throwing things out…so on that first day, I took the remainder, added a bit of flour and made a flatbread with it. Yey! Lunch!

Day 3: By the third day, you’ll likely see some activity — bubbling; a fresh, fruity aroma, and some evidence of expansion. It’s now time to begin two feedings daily, as evenly spaced as your schedule allows. For each feeding, weigh out 4 ounces starter; this will be a generous 1/2 cup, once it’s thoroughly stirred down. Make flatbread out of any remaining starter. Add another cup of flour and 1/2 cup cool water twice daily.

Repeat feeding every 12 hours, measuring out 1/2 c starter, adding flour and water to it, and making flatbread out of the rest. On the 6th or 7th day, you should have some nice sour starter. Now you can move it to a permanent home–a jar with a screw-top lid and store it in the fridge. It will only need feeding about once a week.

When you want to start making sourdough bread, go watch this video: It’s Binging with Babish, or rather Basics with Babish, who covers all the steps to making a great loaf of sourdough without using yeast. It takes time and patience and the proper tools (as well as time to play video games). It’s funny and informative…and a bit long.
I didn’t see the video before making my first sourdough loaf, but it still turned out OK.

I used a “rustic no-knead bread” recipe and added about 1/2 cup of starter to it. I also added yeast, so it’s not a full-on sourdough-only loaf. I’m going to try that soon, though!