Substituting must with green harvested wine or water to produce lower alcohol wines

By Karien O'Kennedy
The aim of this study was to investigate two blending strategies to produce lower alcohol wines and comparing it to wines produced from earlier consecutive harvest time points. The study focussed mainly on the polysaccharide and tannin content of the resulting wines as these two parameters are associated with mouthfeel, astringency and perceived hotness. No sensory results were published in this study.

Project layout:
  • Cabernet Sauvignon grapes were harvested in 2015 at four consecutive dates resulting in wines with alcohol levels ranging from 11.4% to 18.2% (control).
  • Cabernet Sauvignon grapes were harvested at about 8°Brix and fermented with EC1118. The resulting green harvest wine (GHW) had an alcohol of 4.5% and pH of 2.76. Fermentation was sluggish but completed due to the very low pH being inhibitory to yeast.
  • Juice from the control harvest was substituted from 10 - 14% of either GHW or water - yielding alcohol levels of approximately 17%, to up to 30 – 40% - yielding alcohols of approximately 14.5%.
  • Researchers measured mainly polyphenols (colour and tannin) as well as polysaccharides in all wines produced.

Results:
  • Polysaccharides (contributes to fullness and decreased astringency) increased with berry ripening but decreased as berry shrivel commenced in over ripe grapes.
  • Anthocyanins, tannins and colour density increased with later harvest times.
  • Blending must with high percentages of GHW or water resulted in increased polysaccharide concentrations in final wines.
  • There were no significant differences in anthocyanin and tannin concentrations in blended wines.
  • High proportions of GHW and water did initially decrease stable colour pigments but after 18 months of bottle ageing there were no significant differences between treatments.

Follow up research not yet published:
  • Chemical and sensory analyses of the 2015 wines have been conducted.
  • Trial was repeated in 2016 and Shiraz was evaluated in addition to Cabernet Sauvignon.
  • Evaluations in 2016 were done under more moderate harvest conditions, without berry shrivel.
  • In 2017 water addition was compared with water substitution.

Significance of the study:
Pending the sensory study outcome of this research the substitution of must with either GHW or water seems a very real possibility to successfully produce wines with lower alcohol levels, as desired by consumers. Although water addition is not legal in South Africa (legal in the US and Australia), the use of GHW can be explored. An application to legalise water addition should probably be considered in South Africa.

References:


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