Grape juice, clarification

Leong, L.S., Hocking, A.D., Scott, E.S. (2006b). The effect of juice clarification, static or rotary fermentation and fining on ochratoxin A in wine. Aust. J. Grape Wine Res., 12, 245-252. 

Figure 9. Effect of processing and storage on the phenolics of Thompson Seedless grape juice. Unit operations code P, pressed juice E, enzyme clarification Ft, filtered B, bottled single-strength juice C, concentrate and CS, stored concentrate.

Commercial pectolytic enzymes used in clarification can cause hydrolysis of hydroxy cinnamic acids in apple, pear and grape juice [183]. In addition, the use of gelatin as a fining agent reduces total phenolics with the polymeric phenolics being the most affected. 

Removal. Use of pectolytic enzymes as an aid to the clarification of grape juice has been studied by Willaman and Kertesz (1931) and Mehlitz and Scheuer (1934). Hickinbotham and Williams (1940) and Besone and Cruess (1941) used commercial preparations successfully for clarifying the must. The resulting wines also clarify more rapidly. Cruess and Kilbuck (1947) added the enzyme to the crushed grapes to increase the juice yield. They obtained 6.5% more free-run juice when one part of the enzyme was added to 1000 of the crushed grapes, which were then allowed to stand overnight. They claimed the wines cleared more rapidly. 

High levels of rot in the harvest increase juice turbidity and make clarification difficult, due to the protective colloidal effect of glucan produced by Botrytis. A low concentration of rot (less than 5%) tends to facilitate juice clarification, due to a pectinase activity in contaminated grapes that is nearly 100 times higher than in healthy grapes. 

Clarification (apple juice, pear juice, grape musts or wines)... 

Muhlack, R., Nordestgaard, S., Waters, E.J., O Neill, B.K., Lim, A., Colby, C.B. (2006). In-line dosing for bentonite fining of wine or juice contact time, clarification, product recovery sensory effects. Aust. J. Grape Wine Res., 12, 221-234... 

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