Mix 100 g flour with 100 cc water, cover and let rest for 24-48 h at 20C.
Add same amount and mix well, cover and let rest for 24 h.
Add 200 g flour and 200 cc water, mix well, cover and let rest for 24 h. It should have an appetizing acid smell and will last for 1 bread (other recipi), leaving a rest of 100 g leaven for the faster leaven-increase. Leaven-increase: add 100 g leaven, 350 g rye-flour and 350 cc water(40C), mix well and let rest for 12-24 h at 20C. Between two baking-circles you can store the leaven-rest in the fridge up to 8 days.
For longer storing (up to four weeks) add rye-flour to the leaven til it gets crumbly.