Day 1, in the morning: In a bowl mix 100 g water, 50 g rye flour, and 50 g white flour. Transfer into a clean jar, cover loosely, and leave the culture at room temperature (warm spot) for 24 hours.
Day 2 in the morning: You should see some bubbles in it. Discard all but 75 g of the culture which you transfer into a clean bowl. Feed this with 75 g water, 25 g rye flour, and 50 g white flour. Wash the jar with simply warm water and transfer the culture into the jar. covered loosely. Let it sit at room temperature (warm spot) for 12 hours.
Day 2 in the evening: Even if the signs of activity might not be visible, repeat the process as in the morning, discarding all but 75 g of the culture which you transfer into a clean bowl. Feed this again with 75 g water, 25 g rye flour, and 50 g white flour. Transfer to the clean jar, cover loosely, and let it sit at room temperature (warm spot) for 12 hours.
Day 3 – repeat feeding the culture every 12 hours as in day 2, 75 g culture, 75 g water, 25 g rye flour, and 50g white flour.
Day 4: On day 4 you may see visible signs of life, the culture is bubbly and raised in volume. Continue feeding every 12 hours, same ratios as in previous days.
Day 5: Once the starter doubles in volume you can feed the starter using only white bread flour. So it will be 75 g starter, 75 g water, and 75g white bread flour, which is 1:1:1 ratio (equal amounts of starter, water and flour). Repeat feeding the starter every 12 hours.
Day 6-7: From this moment you have a 100% hydration starter, that is bubbly and has a sour smell, that doubles in 8 hours or less, that should be strong enough to be able to bake your first sourdough bread. You have succeeded!
Repeat feeding the starter every 12 hours for 14 days to make it stronger. Sourdough starter will rise and deflate between feedings and it gets stronger and active with each feeding process.