Tonight we decided that we wanted to see what happens to marshmallows if you put them in the dehydrator. So we took out a fresh bag of mini-marshmallows and divided them onto two trays. Put the dehydrator temp on high and then checked the progress every 10 minutes. The only changes that were visible were that they puffed up slightly and the outsides were kind of crispy - middle stayed gooey. So after 30 minutes we decided to leave them in for 30 more minutes longer to see if they would crisp up even more. Well they did, and the funny thing was that they stayed puffed up. When we went to pour them back into the measuring cup, we couldn't fit them all.
Many people claim that leaving the bag open on the marshmallows will dehydrate them, but I have to disagree, I think it just makes them stale. Dehydrating actually makes them brittle. And I think that's pretty cool!