You’ll need your dried sourdough starter, all purpose flour (it’s fine to feed white bread flour, but AP is cheaper), a kitchen scale, a spoon, and a pint jar with lid for this. All of this takes place on your kitchen counter. I use tap water, but ours isn’t chlorinated so I’d recommend filtering yours if it is.
Let’s revive those flakes-
Put your dried starter in the jar. Your starter weighs 20 grams and you’re going to add 20 grams of lukewarm water to it. Smush the starter flakes down into the water and cover loosely (just don’t screw the lid on all the way.) Go back and give this a stir every hour for a few hours.
After a few hours, the flakes should have soaked up the water and turned into a paste. Add 20g cold water and 20g AP flour and stir to completely combine. I scrape down the sides of the jar with the tip of the spoon all the way around so the jar stays fairly clean and transparent, so you can see the rise. I also like to put a rubber band around the jar right where the starter hits when it’s first stirred up, also to gauge the rise. Cover loosely.
Rinse all your tools well right away. Flour and water makes glue and it will glue everything it gets on.
In 24 hours, you should have bubbles. Hooray, it’s awake and alive!
Now, discard all but 3 TBSP or so of starter and feed it 50g cold (always cold from here on in) water and 50g AP flour. To make my life easier, I just discard most of the starter, then put the jar on the scale and tare it before adding water and flour. This is how I feed my starter every 24 hours. I do it in the evening so it’s big and bubbly and ready in the mornings for a big feed on the days I start bread.
Some people build a separate levain for bread baking, but I just keep my starter in a big enough jar and feed it enough that I have plenty for bread baking with a little left over to do my usual 50g/50g daily feed to continue on. My usual bread recipe uses 100g starter, so I am ready to go to bake one loaf at any time with my starter as-is. If I want to bake more than one loaf, I can double feed in the jar (mine holds 20 oz. and this fits in it) or take some starter out to a bowl and feed it there for however many loaves of bread I’ll be starting later.
If I feed in the morning to build up for bread, the starter will be ready to go by 3 pm when I want to start dough for baking the next morning.
Visit my bread post for my recipes and links to others.