As a new sourdough baker, I still have some disappointments, but I finally nailed this recipe, two beautiful loaves. But my loaves were not nearly as dark as Martin's. I used the same recipe, same temps, dusted with whole wheat flour and cooked to an internal temperature of 207-209. I have a gas oven, and did not use the convection. I cooked 20 minutes in the covered cast iron dutch oven, and 25 with the cover off. Any ideas how he get's such a dark crust? Thanks.

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