Project 4.1.1

Managing the impact of vintage advancement and compression

Project summary

Vintage compression places significant stress on harvest and processing logistics and capacity. However, the contribution to this phenomenon of management practices (e.g. improved irrigation or pruning), has not been separated from the effect of higher temperatures. In addition, trends in fruit maturity parameters other than sugar accumulation need to be investigated, as does the balance between titratable acidity (TA) and pH with sugar concentration. A better understanding of these trends will corroborate their likely relevance in future vintages, and inform both winery and vineyard management decisions.

Another important symptom of vintage compression, is delays in harvesting fruit and resulting high sugar/alcohol concentrations. Increases in grape sugar concentrations can be driven by the import of sugar from the vine, or by berry dehydration. Dehydration also results in a loss in yield, with a significant impact on vineyard profitability. A better understanding of the dynamics of sugar accumulation and aroma-relevant grape compositional changes, may aid harvest decisions and inform appropriate compensation for delays in picking fruit.

Another option to manage vintage compression is to increase the speed at which fruit can be processed. For red wines the major processing bottleneck is red fermenter capacity. Faster extraction techniques (including thermovinification and flash détente) can reduce the time that red ferments need to be in contact with skins. Unfortunately, these techniques can produce undesirable or non-traditional flavour profiles, which may make their adoption less attractive to industry. A range of extraction processing options will be investigated for red grapes on a commercial scale, to target more desirable and familiar colour, texture, and flavour outcomes.

The research plan includes:
• an extension of the analysis of the maturity dataset from Treasury Wine Estates for TA and pH, in order to track changes in these parameters (and their balance with sugar) from the late 1990s
• an evaluation of models for assessing the likely impact of climate change on TA and pH (and their balance with sugar)
• data analysis across a range of research data sets (already collected) of sugar accumulation and berry weight, to separate the impact of sugar importation vs berry dehydration
• characterisation of the impact of the amount, timing and methods of water addition on wine composition and style.

Additional chemistry and sensory support will be provided from Projects 3.1.1 (volatile aroma compounds) and 3.1.4 (managing wine extraction).

Latest information

Can dilution of grape must address the effects of vintage compression without a loss of wine quality?
Vintage advancement and compression can result in the intake of fruit at higher sugar levels, due either to rapid ripening rates or the lack of resources to harvest fruit in the required timeframe. A study was undertaken with Barossa Shiraz to compare earlier harvesting (at 13.5, 14.5 and 15.5°Baume) versus dilution (lowering of grape must to 13.5 and 14.5°Baume) as potential approaches to achieve lower alcohol wines with positive sensory characteristics. Dilution was conducted either via the direct addition of water, or by running off juice and replacing it with water. It was found that dilution reduced wine tannin and colour independently of the mode of dilution. However, diluted wines had consistently higher tannin and colour than wines made from early-harvested fruit at an equivalent wine alcohol concentration. Sensory analysis showed that the wines could chiefly be defined by differences in ‘dark fruit’ aroma/flavour, hotness, viscosity and opacity. The 15.5°Baume wines were all rated higher in these attributes. These attributes were reduced in wines with lower alcohol, with the earliest harvest (13.5°Baume) rated lowest for all. The results showed that lowering must sugar to 13.5°Baume using dilution was more beneficial for both colour and sensory outcomes than earlier harvest, and the mode of dilution had little impact.