Ruisleipä, the slow way
Proper ruisleipä is made from rye and nothing else. No wheat to hold it together, no yeast from a packet. It is dense, sour and keeps for a week, which is exactly why it has been on Finnish tables for centuries.
Evening: the leaven
Mix 50 g of active rye starter with 300 g of wholegrain rye flour and 400 g of warm water (around 35 °C). Cover and leave it somewhere warm for 12 to 16 hours. It should smell sharply sour and look like porridge full of holes.
Morning: the dough
Add 400 g more rye flour and 12 g of salt. Do not try to knead it: rye dough behaves like wet clay. Work it with a spatula, then with wet hands shape one large round or two smaller flat ones. Press a hole through the middle if you want the traditional reikäleipä.
Proof until the surface cracks like dry earth, usually 1.5 to 3 hours. Prick the top all over with a fork.
Baking
10 minutes at 250 °C, then 40 to 50 minutes at 200 °C. Brush with hot water when it comes out and wrap it in a towel. The hardest part: wait until the next day before slicing. The crumb needs that time to set.