Sometimes if you add during the time you are adding baking soda or other agents you will get a chemical reaction. Now they are mainstream and raisins have always been a part of this phenomena. Here is a document on Raisins in Performance Bars . Sugaring - Crystallization or sugaring, refers to the formation of glucose monohydrate crystals in raisins after drying. It does not effect the skin or internal structure of the raisin.
Crystallization is a naturally occurring process of nature.
We see crystallization in raisins, in just about every crop year, from producer to producer, region to region. Typically it occurs more often in higher moisture raisins with a high glucose content. Crystallization does not affect or deteriorate the nutritional or functional nature of the raisin. When stored in humid areas, they tend to pick up moisture. This will accelerate crystallization.