Pre-fermentative Treatment of Grape Juice and Must from Vranec Variety with a Glucose Oxidase from Aspergillus niger

Abstract

High concentration of fermentable sugars in the grapes in the moment of harvest leads to obtaining wines with high concentration of alcohol. Certain grape varieties, such as the Vranec variety, are prone to reaching higher levels of sugar concentration, especially in warm and dry regions. This problem is accentuated in the recent years with the augmentation of the average temperature and shortening of the vegetative season due to global warming. One of the methods for reducing the alcohol level in these wines is by using an enzymatic pre-fermentative treatment with glucose oxidase from Aspergillus niger. This treatment was done on two modalities – crushed grapes (as grape must) and pressed juice. The efficacy of this treatment was demonstrated by measuring the level of gluconic acid in the juice and the must after the treatment using HPLC analysis. In the second modality higher efficiency was obtained, lowering the concentration of glucose for 28%. This treatment affects only part of the glucose, leaving the rest of it and the fructose available for fermentation by the yeasts. The final product is not a completely dealcoholized wine, but wine with lowered alcohol concentration. This type of product can be used for blending with traditionally fermented wines in order to make a correction of the final alcohol level.