I've been making lots of granola batches lately, and for some reasons whenever I include raisins in the batch, after the granola is done baking, the raisins are rock hard. I'm looking for a nice, chewy consistency. I usually bake it at 300 degrees for about 40 minutes, in the middle rack, stirring it every 15-20 min. What am I doing wrong? And how do I get the raisins to stay nice and chewy?