Build your levain: In a glass jar or a small mixing bowl, thoroughly mix 20g of active starter, 50g of rye flour and 50g water. I usually build levains with water roughly at room temperature, since it's going to be sitting at room temperature for so long anyway. 

Cover your levain and leave it on the counter for 12 hours.

After 12 hours, check your levain for readiness- it should have risen in the container, and the bottom and sides should show a lot of little bubbles. The top of a rye starter may not appear bubbly but should have a cracked appearance. If these signs are not present leave the levain to ferment for 30 more minutes and check again.

Add remaining rye flour, bread flour, molasses, remaining water, salt and ripe levain to a large bowl. Use a dough whisk or wooden spoon to thoroughly mix the dough. It will be a somewhat sticky dough at this stage and will have a shaggy appearance. Cover your mixing bowl with plastic wrap or a damp tea towel and leave on the counter (ideally in a warm place) to rise.

Because rye flour has less gluten than white flour, it doesn't benefit as much from stretch and folds, the purpose of which is gluten development. However, since this recipe also contains bread flour, I usually do a couple of thorough sets of stretch and folds with wet hands, at about 30 minutes and 1 hour into bulk fermentation. After, cover your dough and let it sit for the remainder of bulk fermentation.

Bulk fermentation time will vary for this sourdough rye recipe, depending especially on the temperature of your kitchen. Since I've been testing this recipe mostly in colder months, I've needed to stretch bulk fermentation to as long as 5.5 hours. For those of you not baking in colder climates, closer to 4 hours may suffice. Remember to check your dough and not just the clock!

When bulk fermentation is complete, the dough should have risen visibly in the bowl and have a smooth, domed appearance. You will likely see small bubbles scattered throughout, especially at the sides and bottom of the bowl (an advantage to using a clear glass mixing bowl). 

Lightly flour a work surface and prepare a proofing basket.

Use a dough scraper to turn your dough out onto your work surface and shape into either a boule or a batard (my preference!). Use your bench scraper to gently transfer your loaf into your proofing basket and cover with plastic wrap or a plastic bag.

Place your proofing basket in the fridge, overnight or for up to 36 hours. 

When you're ready to bake, preheat your oven to 450 degrees.

To bake in a Dutch oven: Transfer your dough from your banneton onto a piece of parchment paper. Score the dough with your bread lame, then place it into your Dutch oven. Bake in the preheated oven with the lid on for 20 minutes, then remove the lid and continue to bake for 27-32 more minutes.

To open bake: If you have an open baking surface such as a pizza stone, preheat the oven with the surface inside it. I also put a loaf pan in the bottom of the oven while it is preheating. Put the loaf on a piece of parchment paper and score it with your lame. Use a pizza peel to slide the parchment paper & loaf onto your baking surface, then dump a big cupful of ice cubes into the hot loaf pan to create steam (the Dutch oven lid does this for you). Bake for 20 minutes then remove the steaming pan and bake for 27-32 more minutes. 

Let your loaf sit and cool for at least 2 hours before slicing into it.