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Improving consistency from the grape to the glass; from the vineyard to the wine.

 

Introduction

Vineyards are complex variable systems and perennial crops change from season to season. In any vineyard you have variability from soil and geography; you also have the harvest ripeness of the grapes to consider and the cultivation practices imposed. An interesting question, which was asked, is do enzymes have any impact on vineyard variability brought from the grapes harvested at different ripeness levels into the winemaking? How do enzymes effect this variability? Does the enzyme addition show up in the wines produced? These became the major questions asked in this research study.

 

Experimental layout

The research plan1 was conducted on the semi-commercial Welgevallen Cabernet Sauvignon vineyard of the Institute for Wine Biotechnology in the Department of Viticulture and Oenology of Stellenbosch University. The vineyard was partly managed as a model vineyard and the experimental plot was subdivided into panels. The checkered-board panel design comprised six vines per panel and a total of 24 panels were used for the experiment. The vineyard was identified optimal for harvest at 24°Brix. However, individual panels varied quite dramatically in average Brix values. The range of actual ripeness levels ranged from 19 – 26°Brix in some cases. Although the majority of grapes averaged between 22 – 25°Brix, the level of variation was quite significant.1

The variable level of ripeness in the panels also meant that the grape cell wall layers were quite different. Cell walls in grapes consist of pectin that is a polymer made up of many sugar acids. Pectinases are a common type of wine enzymes that can break down these grape pectins during fermentation.2 Differences in cell wall layers mean that grapes harvested from the various panels showed different degrees of berry intactness. Berry integrity is important as this can determine how much juice (must) and also colour pigments and polyphenols can be extracted from a particular area in the vineyard. It was also not clear if enzymes could play any role in this at the beginning of the study. Therefore, an experiment was performed to see the effect of enzymes on grape ripeness variability within highly (intra-vineyard) variable regions.

 

Results

Half of the panels were treated with commercial enzymes, whereas the other half were not treated and assigned as controls. Wine grapes harvested from the untreated (control) panels showed major variations in the volume of must and wine obtainable, as well as variation in extractable components. Colour pigments and tannin levels were also highly variable from the untreated panels. On the other hand, enzyme treated panels showed much more improved consistency of total polyphenol amounts between panels. The grapes had been substantially de-pectinated (degraded or broken down) by the enzymes added, even in those grapes at 19°Brix, which showed high pectin intactness.2 The panels treated with enzymes showed greater volumes of must and wine produced. These enzyme treated panels produced wines with more polymeric tannins, more colour and complex pigments.

What was also noted, is that enzyme treated panels did not show increases in methanol levels, an unwanted by-product in wine fermentations. The deeper colour and higher tannin levels lasted in the enzyme treated wines for well over a year at final measuring. There were no significant differences in other parameters, such as alcohol content, pH and total titratable acidity, between wines, showing that the enzymes acted mainly by accessing the skin cell layers where all the pigments are to be found.

 

Significance of the study

This study would suggest that enzyme addition may be beneficial if you are working with a vineyard that showed a large degree of internal ripeness variation (lack of synchronicity of grape bunches), or if forced to harvest earlier than planned. The study also showed that enzymes worked most effectively on ripeness levels of 24°Brix or lower, where berry pectin is still quite intact. Overripe grapes of greater than 25°Brix did not respond to enzyme treatment as their berry layers were already broken down. What this means, is that use of enzymes needs to be managed with knowledge of the vineyard conditions.

What appears really important, is optimal ripeness measurements and probably also phenolic ripeness tests need to be conducted in the vineyard first in order to decide whether enzymes should be considered by the winemaker later on. This research has opened up a new avenue of thinking about the role enzymes play in winemaking.

 

Future research

Benefits from future research involve knowing more about how the dosage and type of enzyme combinations that could be used to tailor applications to specific cultivars and vineyard scenarios. What would be most interesting, is to know if the combination of ripeness variability with enzyme addition influences the sensorial properties of the wines produced. Mouthfeel, astringency and bitterness, for example, in red wines should be able to be modulated by combining grape ripeness with enzyme addition. However, no studies have fully tested this in a combinatorial design yet. What is clear, is that careful use of enzymes in combination with using vineyard and ripeness knowledge has the potential to enhance the complexity, colour stability and ageing potential of South African red wines.

 

References

  1. Gao, Y., Fangel, J.U., Willats, W.G.T., Vivier, M.A. & Moore, J.P., 2016. Effect of intra-vineyard ripeness variation on the efficiency of commercial enzymes on berry cell wall deconstruction under winemaking conditions. Journal of Agricultural and Food Chemistry, DOI: 10.1021/acs.jafc.6b00917.
  2. Gao, Y., Zietsman, J.J., Vivier, M.A. & Moore, J.P., 2019. Deconstructing wine grape cell walls with enzymes during winemaking: New insights from glycan microarray technology. Molecules 24(1), 165.

 

– For more information, contact John Moore at moorejp@sun.ac.za.

 

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