The effect of Uncinula necator (powdery mildew) and Botrytis cinerea infection of grapes on the levels of haze-forming pathogenisis-related protiens in grape juice and wine

Copyright © 2008 Australian Society of Viticulture and Oenology Inc.Powdery mildew on Chardonnay grapes resulted in increased levels of a grape thaumatin-like protein, VvTL2, in the free run juice compared to that from uninfected grapes. These increased levels persisted through winemaking and at the highest level of infection (> 30% of bunches infected) had a significant impact on the haziness in the wine following a heat test. Infection of Cabernet Sauvignon grapes (1-20% of bunches infected) did not affect the protein concentration of free run juice, and only traces of pathogenesis-related (PR) proteins remained detectable in the Cabernet Sauvignon wines from either infected or healthy grapes. In contrast, infection of Chardonnay or Semillon grapes by Botrytis cinerea in the vineyard resulted in decreased levels of all PR proteins in the free run juice and in a total protein extract from infected berries compared to that from uninfected grapes. Similar trends were observed when B. cinerea was grown in the laboratory on surface-sterilised berries or in filter-sterilised juice.Teresa Girbau, Belinda E. Stummer, Kenneth F. Pocock, Gayle A. Baldock, Eileen S. Scott and Elizabeth J. Water

Preventing protein haze in bottled white wine

Slow denaturation of wine proteins is thought to lead to protein aggregation, flocculation into a hazy suspension and formation of precipitates. The majority of wine proteins responsible for haze are grapederived, have low isoelectric points and molecular weight. They are grape pathogenesis-related (PR) proteins that are expressed throughout the ripening period post véraison, and are highly resistant to low pH and enzymatic or non-enzymatic proteolysis. Protein levels in un-fined white wine differ by variety and range up to 300 mg/L. Infection with some common grapevine pathogens or skin contact, such as occurs during transport of mechanically harvested fruit, results in enhanced concentrations of some PR proteins in juice and wine. Oenological control of protein instability is achieved through adsorption of wine proteins onto bentonite. The adsorption of proteins onto bentonite occurs within several minutes, suggesting that a continuous contacting process could be developed. The addition of proteolytic enzyme during short term heat exposure, to induce PR protein denaturation, showed promise as an alternative to bentonite fining. The addition of haze-protective factors, yeast mannoproteins, to wines results in decreased particle size of haze, probably by competition with wine proteins for other non-proteinaceous wine components required for the formation of large insoluble aggregations of protein. Other wine components likely to influence haze formation are ethanol concentration, pH, metal ions and phenolic compounds.E.J. Waters, G. Alexander, R. Muhlack, K.F. Pocock, C. Colby, B.K. O'Neill, P.B. Høp and P. Jone

Grape and wine biotechnology: challenges, opportunities and potential benefits

The image of wine as a harmonious blend of nature, art and science invites tension between tradition and innovation, and no tension in the business of making wine is greater than that brought into play by the potential afforded by 21st century grape and wine biotechnology. The challenge is to realise the potential of technological innovation without stripping the ancient art of grapegrowing and winemaking of its charm, mysticism and romanticism. Equally challenging is the multitude of complex and interconnected agronomic, business, regulatory and social obstacles currently blocking commercial availability of transgenic grapes, wine yeast and malolactic bacterial starter strains. While the need to assess rigorously the potential negative impacts of new technologies is self-evident, over the long term, failure to overcome these hurdles will disadvantage the international wine sector and consumers alike. This contention is illustrated with reference to recent examples of genetically improved grapevine, yeast and bacterial prototypes showing potential for enhanced, cost-effective production of wine with minimised resource inputs, improved quality and low environmental impact