I've been baking whole-grain breads (grind my own with a Country Living Grain Mill) exclusively for a couple of years now, and am reading and using Peter Reinhart's Whole Grain Bread Book for the past month or so. The breads are coming out great most of the time, but I find that the top of my soaker (which I've never used before reading this book) is grey in the morning, like guacamole without the lime juice. Kitchen temp is below 60 all night, and the starter in the 'fridge is just fine... I thought it must be oxidation inside the container, and tried pressing plastic wrap on the surface before covering the bowl. Didn't work. Last night I put the soaker into a plastic zip-bag and squeezed out all the air. This time, the whole surface was grey. Could this be a reaction to the plastic? Does anyone have a magic trick they can share with me?