Helpline provies the readers of Process Heating with a chance to solve problems that crop up in their heat processing applications.

I am trying to dry apple slices. Right now, we're having trouble with the apple slices developing a "skin" on the surface. Someone suggested that we have to let the fruit rest between heating stages. How do I figure out how long to let it rest? -- I.C.

The "skin effect" is probably due to the surface drying faster than the interior of the slice. The questioner does not indicate the method being used to dry the apple slices. The heat transfer method does affect the process. -- Morton Nemiroff, (808) 261-5786 or saltyret@juno.com