A lot of the recipes on Jack Keller's website require golden raisins. Does anyone think there will be a big problem if I use white grape juice concentrate instead of golden raisins? Does anyone have any experience with this?
I've read, I can't remember where, that raisins as being a good way to add body to a lightly flavored mead. It could be that he's going for that more than flavor and you wouldn't get it from grape juice.
+1 on the body and nutrients. I have added golden and regular grapes in several wines, I have also used Zant Currents. If Jack Keller suggests it, do it, as he is quite knowledgeable and experienced in wine creation.
I will also add that you might want to consider rehydrating your raisins before attempting to slice them and especially before attempting to puree them. Those suckers suck to chop.