Stir together the rye flour and water in a glass jar until they are fully incorporated and no dry flour remains. A little more water can be added if needed.
Cover the jar with a lid or a towel and leave it in a warm room temperature place away from cold drafts.
Let it sit for 24 hours.
Day 2
After the first 24 hours you may not see any bubbles forming and that is ok.
Feed the starter 1/2 cup bread flour and 1/4 cup water and stir to combine well. A little more water can be added if needed so that there is no dry flour in the starter.
Cover the jar and let it sit for another 24 hours.
Day 3
At this time small bubbles can usually be seen forming in the jar.
Discard approximately half of the starter and feed the remaining starter with 1/2 cup bread flour and 1/4 cup water and stir to combine.
Cover the jar and let it sit for another 24 hours.
Day 4 and Beyond
Feed the starter with 1/2 cup bread flour and 1/4 cup water every 24 hours, discarding approximately half every other feeding.
If it is very warm in your house you may need to feed the starter twice per day.
Once the starter is bubbling up after every feeding, it is ready to use in recipes.
Video
Notes
The sourdough starter can be kept in the refrigerator when not in use. Simply put the jar covered with a lid in the fridge right after feeding it. It will keep for about a week at which time it will need to be fed again. Bring the starter to room temperature and feed it before using it in recipes.
Please see the full blog post for troubleshooting tips and FAQ's.