My sourdough turned purple after a cold ferment, still not sure why

Left a batch in the fridge for 3 days in Portland and it came out with this weird purple tint on the crust. Smelled fine, tasted fine, but I've baked sourdough for 6 years and never saw that before. Turns out the rye flour I used had a higher anthocyanin content, which reacts with the acidic starter. Has anyone else gotten purple loaves from a long retard, or was my fridge just messing with me?

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jesse_cooper22d ago

Gonna have to disagree with the anthocyanin theory. Rye does have that pigment, but for it to show up that strong after a cold ferment something else is usually going on. I've seen purple crusts before and it was almost always from the starter getting too acidic and reacting with trace minerals or even the pan if you used a metal one. 3 days in the fridge is long, but not crazy long, so I bet your starter was on the hungry side and dropped the pH more than usual. Also, Portland tap water can be weirdly alkaline, which throws off the acid balance in the dough. You said it tasted fine, which makes me think it's not mold or contamination, but a chemical thing that's more about your process than the flour. Maybe cut the cold ferment to 24 hours next time or feed your starter right before the retard and see if the purple goes away.