Use of fresh versus frozen or blast-frozen grapes for small-scale fermentation

Frank Schmid, Vladimir Jiranek
School of Agriculture, Food and Wine, The University of Adelaide; and Wine Innovation Cluster, The Waite Campus, Glen Osmond, South Australia, Australia

Background: This paper firstly examines the validity of using laboratory-scale fermentations as a means of correlating winemaking outcomes with larger industrial scale fermentations. Secondly, conventional and blast-freezing of whole bunches were investigated for their relative suitability as methods of preservation as determined by the nature of the resulting wines.
Methods: Red must fermentations were compared at the laboratory 80 kg scale, and the more industrially representative 500 kg pilot scale. Fermentation profiles and duration for both scales were found to be very similar. Whole bunches were either slow/conventionally frozen (−20°C), or quickly/blast-frozen (−25°C).
Results: Wines made from frozen grapes compared well with the wine made from the fresh must. Color and chemical analyses of the wines revealed few differences. A duo-trio sensory evaluation showed that wine from blast-frozen grapes was more similar to the fresh wines than wines from conventional frozen grapes.
Conclusion: The findings of this research suggest that whole-bunch blast-freezing of grapes is preferable to conventional freezing.

Keywords: wine color, research winemaking, frozen grapes