How to make raisins using a dehydrator
Because grapes have a rather tough skin it is recommended if you want to dry them whole that you dip the grapes in boiling water for 30 seconds or more to crack the skins and then immediately put into ice water, drain on a paper towel and then put on your dehydrator trays to dry. You can also cut larger grapes in half, remove seeds if they have them, and then place them on the dehydrator trays with no pretreatment.
Instead of dipping them in boiling water I have also found that if you freeze them single layer on a cookie sheet and then place them on the dehydrator trays the freezing will also crack the skins.
Grapes are kind of like plums, they take a long time to dry. It may take 15-24 or more hours to dry them so be patient.
If you need further information on drying fruits and vegetables Extension has a nice publication you can download on line. Go to to our extension FCH website: http:extension.oregonstate.edu/fch/food-preservation. go to drying and it is PNW 397.
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