In a large mixing bowl, combine the sourdough starter, water, wheat flour, and rye flour. Mix until all the ingredients are fully incorporated, ensuring there are no dry spots. The dough will be sticky and dense, which is expected due to the rye content. Cover the bowl with a clean towel and allow it to rest for 1 hour to fully hydrate the flour.

After the initial rest, add sea salt and gently mix it into the dough. Perform the first stretch and fold technique by grabbing a section of the dough, stretching it upward, and folding it over itself. Repeat this process several times, rotating the bowl as you go. Cover the bowl and allow the dough to rest.

Over the next 90 minutes, complete two additional sets of stretch and folds, spacing them 30 minutes apart. This technique helps develop the gluten structure without requiring traditional kneading.

Cover the dough and let it ferment for 4 hours at 78ºF (25ºC). The dough should expand and develop a slightly airy texture but will not double in size as wheat-based doughs typically do.

Lightly flour a clean work surface and turn the dough out onto it. Divide the dough into two equal portions using a bench scraper. Flatten each piece slightly and shape it into a bâtard (oval loaf shape) by folding the edges inward and rolling it up gently.

Place the shaped loaves into well-floured proofing baskets or cloth-lined bowls, seam-side up.

Allow the loaves to proof at room temperature until they pass the finger poke test—when gently pressed, the dough should slowly spring back, leaving a slight indentation. The proofing time will vary depending on room temperature.

Preheat the oven to 480ºF (250ºC). If available, use a baking stone or Dutch oven for optimal heat retention. Additionally, place a baking tray on the lower rack to create steam during baking.

Gently turn the loaves onto a parchment-lined baking sheet. Use a sharp blade or lame to create a scoring pattern on the surface of the dough. This scoring allows the bread to expand properly during baking.

Transfer the loaves to the oven and immediately pour a small amount of water onto the lower baking tray to create steam. Bake for 35-45 minutes, or until the crust is a deep golden brown and the loaves produce a hollow sound when tapped on the bottom.

Once baked, transfer the loaves to a wire rack and allow them to cool completely before slicing. Cutting the bread while still warm may result in a gummy texture.