modified method for production of grape juice concentrate

utilizing natural clay in the traditional production of the grape concentrates in the villages cause the input of large amounts of some metals (solutes) in the product which will be harmful for the consumers. to eliminate the natural clay from this procedure in non-industrial scale, bentonite was selected as an aid-clarifier and examined in treatments under these conditions: two levels of bentonite (1gr/liter, 2gr/liter), primary temperatures of 25, 50 and 80oc, two methods of clarification (with preheating to 65oc and without preheating) and time duration 3 hours. results showed that the clarification of the grape juice concentrate in this scale was the best when 1 gr/liter of bentonite (in jelly form) was added to juice in the room temperature and held for 3 hours before filtration with a suitable cloth and preheating to 65oc. for a product with acceptable taste it should be increased the ph of grape juice after clarification; so for this purpose the addition of na2co3 (about 1.5 gr/liter) is recommended.