Combine 1/2 cup refridgerated liquid sourdough culture, 3/4 cup white flour, 1/4 cup whole grain mix, 1/2 cup water. Mix until smooth. Cover and leave at room temperature for 12 hours.
Add 3/4 cup white flour, 1/4 cup whole grain mix, 1/2 cup water. Mix until smooth. Cover and leave at room temperature for 8 hours.
Mix/knead in 3 cups of white flour 1 cup at a time. Transfer to floured surface and mix/knead one additional cup, or until proper texture. I used about 1/2 cup here. Split into pieces and form/shapes loaves. I went with 2 batards and a boule to rise in my round brotrum. Let rise for 3-4 hours. I cooked the batards after a 3 hour rise and the boule at about 3 1/2.
The recipe calls for cooking 40-45 min at 375, but I prefer to follow Peter Reinhart's method (from BBA) of cooking basic sourdough at higher temperatures for a shorter amount of time. Preheat the oven to 500. Place the loafs on the baking stone and pour 1 cup of water into the cast iron skillet on the bottom of the oven. 30, 60 & 90 seconds into baking open the oven and spray the walls with water. Lower the oven temperature to 450 and bake for 10 minutes. Rotate loaves 180 degrees and bake approx 10-15 minutes or until internal temperature is at least 205 degrees.I was very pleased with how these loaves came out! They had a good crumb, good texture and the mixed grain added excellent flavor. I will be submitting this to YeastSpotting, wish me luck!