In a 2 quart container (1 L), mix all ingredients. Cover with a clean cloth or loose cover (let some air pass, that’s the purpose of fermentation!).
Let stand for two to three days at room temperature. The mixture will rise the second day, do lots of bubbles, then deflate (or a more pleasant smell of fermentation will emerge.) At this point, the sourdough starter is born.
Take ¼ cup (60 mL) of the dough and place it in a clean container. Discard the rest. Add 35 g (¼ cup) of all-purpose flour, 35 g (¼ cup) of rye flour, and ¼ cup (60 g) of warm water. Stir vigorously and cover the container the previous way. Let stand at room temperature for 24 h.
Repeat this operation every 24 hours at room temperature for 14 days or until the mixture changes odor and gives off a sweet and pleasant fragrance. After 14 days the preparation should triple in size in a window 8 to 12 hours of feedings.
Your starter is ready for future use.