Beside chemical pretreatment, some physical pre-treatments
have also been developed for drying grapes. An alternative physical
pre-treatment, consisting of abrasion of the peel of grapes, was
proposed by Di Matteo et al. (2000). They found that the pattern of
the drying curves was quite similar for both chemical (alkaline
ethyl oleate solution) and physical treated samples. Therefore,
abrasion was found to be as effective as the traditional chemical
method. The calculated mass transport coefficient for physical
treated samples was about 4 times greater than that determined for
untreated samples