Okay, I have a customer, albeit, a steady customer, still very, very demanding. She insists on my "painting" her cookies for tomorrow prior to baking. She apparently thinks that by being baked with the paste color on them, that the "chemicals" are released before eating. Okay, what chemicals? LOL. She also insisted that unlike cake batter, I NOT add coloring to the cookie dough. I told her that cookies are not my expertise, but I didn't feel that the paste color would be any problem after the cookies were done (wanted to use a watercolor-type method). Anyway, I don't see how it would be any different than adding paste to butter cream for coloring. It's not cooked afterwards... Still, I want to please my customer...LOL. Anyone know for sure about this???
I don't know about the chemicals in the colors, never heard of that before!
I have painted cookies, though, before baking - if you look in my photos, some of the cookies in the santa cookie bouquet are done that way. It's called "egg paint", and I got the recipe from the Better Homes and Gardens "100 best cookies" 2005 magazine.
Mix one egg yolk with 2 drops water, and add paste food coloring to desired color. Paint on the raw cookie dough before baking, so the egg mixture is fully cooked before eating.
I think it would be much easier to use this method than to try to paint with just the paste or gel colors - the egg mixture is thick enough to coat the paintbrush, so it's easy to get the color right where you want it!
I think your customer has a screw loose. I don't think cooking will help with any chemicals in the food coloring.
I do like the egg yolk method for painting cookies. It gives them a nice shine when they're done from the egg and it's a really easy way to do it.
Not for sale but if you have kids it can be a really fun way to let them decorate something, that's mostly what I use the egg paint for.