To use fresh-milled flour - weigh your grains and stir to combine. Then mill them on the finest setting of your grain mill.
400 g hard red wheat, 100 g spelt, 50 g khorasan
To a large measuring cup, add the beet puree and water. Whisk to combine.
275 g beet puree, 259 g water
Add the beet puree and water combination to the flour. Use your hand or a dough whisk to combine until no dry flour remains in the bowl and a ball forms. Add additional water if it is still dry after mixing for several minutes. Cover the bowl and let autolyse at room temperature for 1 hour.
Add the salt and sourdough starter. Combine with your hand until fully incorporated and a smooth ball forms. Cover and let sit at room temperature for 1 hour.
11 g salt, 100 g sourdough starter
Perform the first stretch and fold by lifting the dough up and over itself 4 times around the bowl. Cover and repeat every 20 minutes for a total of 4 stretch and fold sessions.
After the last stretch and fold, cover the bowl and let sit at room temperature for 2 1/2 - 9 hours. The amount of time depends on the temperature of your house. It takes about 2 1/2 hours when my house is warm. Watch for signs such as many small bubbles around the sides of the dough. It should jiggle when you shake the bowl. An easy hands off approach is to make this in the evening before you go to bed and let it sit at 65℉ for 8-9 hours.
Once the dough is fully fermented, line a 9x5 inch loaf pan with parchment paper. Then turn the dough out onto a lightly wet surface and pat it into a rectangle. Roll the dough up and into a loaf shape, pinching the seams. Place seam side down in the prepared loaf pan. Place in a 2 gallon zip top bag and place in the refrigerator. Leave in the fridge 3 - 16 hours.
Once ready to bake, preheat your oven to 500℉ and set a timer for 1 hour.
Remove the dough from the zip top bag and lift it using the parchment paper and place it into a room temp loaf pan. Score the loaf using a lame or razor blade. Then cover with the third loaf pan.
Place in the oven and reduce the oven temperature to 450℉. Bake the bread 45 minutes covered and an additional 4-5 minutes uncovered.
Cool completely on a wire rack.