Maple Rye Sourdough Boule

Steps

1. Feed the starter about 5 hours before mixing, at equal weights of flour and water, and leave it at about 75°F (24°C). It is ready when it has doubled, looks domed and bubbly, and smells pleasantly sour, usually 4 to 6 hours.
2. In a large bowl, whisk the water, maple syrup and starter until the starter is mostly dissolved.
3. Add the rye flour, bread flour and salt and mix with a wet hand or stiff spatula until no dry flour remains. The dough will be sticky and paste-like; that is normal for a mostly rye loaf. This is about 80% hydration and 2% salt, counting the flour and water in the starter.
4. Cover and bulk rise at about 75°F (24°C) for 3 to 4 hours. During the first hour, do 2 sets of gentle stretch-and-folds 30 minutes apart with wet hands, pulling each side up and over the center. Rye won't get stretchy like wheat dough, so the folds simply firm it up.
5. Bulk is done when the dough has risen by about half, looks puffy and shows small holes and cracks on the surface.
6. Dust a banneton or a towel-lined bowl generously with bread flour. Turn the dough onto a lightly floured counter and, with wet or floured hands, gently pat and tuck it into a round boule. Set it seam side up in the basket.
7. Cover and proof at room temperature for 30 minutes, then refrigerate overnight, 10 to 14 hours. The cold proof deepens the flavor and makes the sticky dough easier to handle.
8. The next day, put a lidded Dutch oven in the oven and preheat to 475°F (245°C) for 45 to 60 minutes. The loaf is ready when its surface shows fine cracks and it springs back slowly when lightly poked.
9. Turn the cold loaf onto a piece of parchment, score a shallow cross or a few lines on top, and lower it into the hot Dutch oven using the parchment.
10. Bake covered for 25 minutes. Remove the lid, lower the heat to 450°F (230°C) and bake 25 to 30 minutes more, until the crust is deep brown and the center reads 205 to 210°F (96 to 99°C).
11. Cool the loaf on a rack for at least 6 hours, ideally overnight, before slicing; rye crumb keeps setting as it cools and will be gummy if cut warm. Slice thinly into 12 pieces.