Translation of ‘Whole-of-Production-Chain’ Wine Science Research to Industry Outcomes (opportunities for lower alcohol)
Abstract
The Australian Research Council (ARC) Training Centre for Innovative Wine Production (TC-IWP) was established at The University of Adelaide with support from industry partners and Wine Australia. It linked scientific and industrial expertise, contributions and facilities of two universities, four scientific organisations and six industry partners. The research of the ARC TC-IWP focused on strategies to reduce the alcohol content of wine through an integrated, whole-of-production-chain approach that starts in the vineyard, continues through fermentation and post-fermentation and finishes with wine consumers. The projects involved in the TC-IWP investigated: early harvest and blending regimes, the use of Saccharomyces and non-Saccharomyces yeast strains, the individual or combined addition of commercially available winemaking additives and the effects of reverse osmosis/evaporative perstraction (RO/EP) treatment on wine composition and sensory properties. Research into the alcohol ‘sweet spot’ phenomenon and consumers’ acceptability for lower alcohol wines is also being conducted. The outcomes have been compiled in the integrated strategy for alcohol and flavour modulations which aimed to deliver new tools or to optimise existing viticultural and winemaking practices to enhance the quality of grapes and wines and define market and consumer preferences for wines with a lower alcohol level.
Summary
In last three decades the average alcohol level for Australian red wines has risen from 12.4% up to 14.4% v/v, which has negative financial implications for winemakers due to higher taxes and increased retail prices. The observed trend in an increasing level of alcohol is partially due to a hotter climate and improvements in viticultural and winemaking practices. Hotter and shorter vintages also put a lot of strain on wineries, which may struggle to process larger amounts of fruit in a very short period. Higher alcohol wines are also driven by winemaker and consumer fondness for aromatic, full-bodied wines. However, there is a growing interest among wine consumers for wines with lower alcohol content driven by health concerns and social issues associated with greater consumption of alcohol (feeling out of control, hangover, not able to drive after drinking) and wine and food pairing. As a result many winemakers are seeking methods to decrease the alcohol content of their wines, without significant effects on wine quality.
The ARC TC-IWP has taken an integrated, ‘whole-of-production-chain’ approach to modulate alcohol levels in wines by developing new and/or evaluating existing viticultural and winemaking methods and techniques either before, during or after fermentation. The following is a summary of the key project areas:
Grape berry cell death
Grape berry cell death is accelerated by impacts of warmer temperatures and elevated evaporative conditions during ripening period, so it is important to understand the mechanisms underlying cell death in order to devise mitigation strategies. The investigations included the physiological aspects (oxygen deficiency and loss of cell vitality) and molecular events (reactive oxygen species (ROS) and ubiquitination in programmed berry cell death) under control, drought and heat stress conditions. During the ripening period the beginning of cell death in berries corresponded to a decreased internal oxygen concentration [O2] and increased levels of ROS. Elevated temperature and water stress accelerated cell death in Shiraz berries and under water deficit berry respiration rate also decreased. A list of genes (e.g. VvBAG1 and VvLOXA) that could be linked to ROS signalling and programmed cell death were identified and VvPub13 was observed to reduce H2O2-induced cell death by inducing genes involved in anti-oxidant responses. The results suggested that bunch shading and irrigation to manipulate plant hydration status may reduce berry cell death and rates of weight loss in Shiraz berries.
The sugar-potassium nexus within the grapevine
For the first time the sugar-K+ relationship was illustrated in individual grape berries and in the grape berry tissues. Potassium and sugar accumulation were closely correlated in the berry pulp, skin and seeds, especially from véraison onwards. However, the sugar content increased more rapidly than K+ with a ten-fold difference observed at harvest. There was also extensive plasticity from berry to berry in the ratio between the two components. A strong ternary relationship between berry K+, sugar and water content was also evident. Rootstock selection and mild water stress through deficit irrigation strategies can be considered for reducing potassium uptake, but this approach is complex due to variety differences, climatic variations and soil variability and warrants further research.
Optimisation of an early harvest and blending regime
An early harvest regime and a blending approach were investigated by i) using either “green harvest wine” (GHW) or water to substitute for some juice prior to fermentation and ii) ‘double harvest’ or blending early and late harvest wines. Large decreases in final wine alcohol concentration (3% v/v) could be readily achieved purely through a pre-fermentation approach. Adjusting the alcohol level via juice substitution led to mostly marginal changes in wine colour density, anthocyanin and phenolic composition as well as wine sensory properties in Shiraz and Cabernet Sauvignon wines. Even in a compressed vintage with a high percentage of Cabernet Sauvignon berry shrivel (2015 vintage) the blending treatments showed promise to produce wines with moderate alcohol concentrations without significantly alternating its quality parameters. In comparison to GHW, the implementation of water was found to be the better way to decrease wine alcohol content due to its ubiquitous availability, low cost and minimal impact on wine composition.
The ‘double harvest’ method of blending early and late harvest final wines may also reduce alcohol level without significant implications on wine flavour profile. Verdelho and Petit Verdot blends maintained sensory profiles similar to those of the wines made from more mature fruit despite being prepared from less ripe grapes. However, dealcoholisation of late harvest wines of Petit Verdot, Verdelho and Shiraz by using a combined reverse osmosis-evaporative perstraction (RO-EP) process to the same alcohol levels as an early harvest (up to -6% v/v) had a significant effect on some volatile compounds such as esters and high alcohols, but not on others (e.g. monoterpenes and C13-norisoprenoids). Changes in the volatile composition of wines reflected in sensory properties of all wines, but it appears that Verdelho wines were the most affected. Interestingly, 13.5% v/v Shiraz wines produced by selecting a specific harvest date, blending or dealcoholisation did not differ for any of the sensory attributes examined. Although similar trends were observed for different varieties, prediction of the dealcoholisation effects on the sensory profile of wines is very difficult due to the complex matrix of the initial wine and the dealcoholisation operating conditions. On another side, the use of a blending practice on wines produced from different harvest dates is an easy-to-adopt, flexible and cost-effective alternative to dealing with increasing levels of alcohol.
Yeast strains in alcohol management and flavour enhancement
The use of yeasts strains capable of yielding lower ethanol in the fermentation is of high interest, as it is does not require additional labour, equipment or handling. Research in this project focused on selection, characterisation and improvement of non-Saccharomyces yeasts for lowering ethanol in wines, whilst enhancing the sensory properties. Firstly, all (to date) commercially available non-Saccharomyces starter cultures were evaluated for their performance in earlier and later harvested Shiraz fruit. The purpose was to test whether the commercial (thus readily-implementable for the industry) non-Saccharomyces treatments have the potential to boost quality of sub-optimally ripe grapes, and/or could they lead to ethanol decrease in later harvest. In comparison to the S. cerevisiae control, enhanced sensory attributes were noted in earlier harvest wines fermented with non-Saccharomyces. However, these treatments were also related to an increased risk of arrested fermentation in higher ripeness conditions. In parallel, characterisation of isolates from un-inoculated grape fermentations in South Australia highlighted a Metschnikowia pulcherrima isolate that, in conjunction with S. cerevisiae, was capable of significantly lowering wine ethanol content (1.2% v/v in white grape juice) compared to the S. cerevisiae monoculture. The ethanol decrease was achieved across a number of conditions without any apparent off-flavour production. Finally, a genetic diversity study of Lachancea thermotolerans was conducted revealing a grouping of isolates based on their geographic origin and isolation habitat. A subset of isolates (94) was further evaluated for their oenological potential in Chardonnay fermentations. They showed great potential in terms of lower ethanol yield and biological acidification due to lactic acid production.
To produce wines with distinctive characteristic winemakers may utilise spontaneous fermentations using ‘wild’ yeasts (non-Saccharomyces) in order to impart some desirable characteristics via a specific intermediates of their metabolic pathways and/or end products. However, the final product is hard to predict, so the aim of this project was to determine the factors influencing the success of spontaneous fermentation in a high sugar environment. Twenty yeast strains were isolated from an in-house collection and tested for physiological responses to osmotic and ethanol stress. Yeast reaction to osmotic stress was clear and similar for all the evaluated strains, while ethanol stress appeared to be more challenging and the responses were more differentiated and genera/strain specific. Torulaspora delbrueckii showed high potential as an alternative to an S. cerevisiae monoculture during wine fermentation, but its performance in a mixed population in a high sugar environment needs to be investigated further in order to allow winemakers to use this yeast species in an informed manner for modulating sensory profile of wines.
Winemaking techniques for alcohol management and flavour enhancement
Additives, such as oenological tannin and mannoproteins, can be used to improve mouthfeel and consequently quality of lower alcohol wines. However, a greater understanding of the compositional consequences of tannin and mannoprotein (MP) additions, and their interactions in the wine matrix, are needed. Trials involving the addition of commercial additives to ‘early’ and ‘late’ harvest Shiraz wines were undertaken, but the outcomes were inconclusive, likely due to the large compositional variation amongst the commercial additives. As a consequence, the composition of 14 grape-based oenotannins and 8 MPs were profiled. Analysis showed that some products exhibited compositions in agreement with the labelled origin of material (i.e. grape seed and/or skin), while others did not. Furthermore, some products were marketed under different names for different oenological purposes, but their compositions were actually quite similar; with the same products marketed by different manufacturers (under different labels) showing significant compositional differences. Based on those results, a subset of tannins and mannoproteins was selected and introduced into wine in different combinations and at different concentrations. However, no significant effect on wine body or astringency was perceivable by sensory analysis. It remains unclear if the difference in tannin levels between treatments was too subtle for the sensory panel to detect, or if the panel needed more training to achieve higher sensitivity. However, significantly different interactions between two selected mannoprotein products and tannin were observed, suggesting that addition of polysaccharide fractions could modify wine polyphenolic composition. Preliminary trials may therefore be required during winemaking to determine the outcomes of their addition in particular wine matrices.
Trials were conducted to investigate the impact of alcohol removal by reverse osmosis–evaporative perstraction (RO-EP). Although the applied technique showed some impacts on wine chemical and sensory properties, they were not detrimental. Some volatile compounds were lost through membrane filtration, which may be considered as the major drawback of this technique. However, only small effects on wine aroma and flavour were observed, which was consistent with the small changes observed in basic wine composition and wine volatile profiles. The perception of hotness was most affected in all wines, but in some wines, body, acidity and bitterness were reduced, while astringency increased, suggesting that the impact of RO-EP depends on the initial alcohol level and wine composition. The ‘sweetspot’ phenomena was investigated, but for now remains undefined due to the time-consuming nature of the exercise, which required involvement of a large number of winemakers with experience in alcohol ‘sweetspotting’.
Novel techniques for flavour enhancement
A novel method of using magnetic molecularly imprinted polymers (MMIPs) to specifically remove methoxypyrazines (MPs) from wines is being developed. A range of molecularly imprinted polymers (MIPs) were synthesised for comparison with their magnetic counterparts and non-imprinted polymers (NIPs), and trialled in Cabernet Sauvignon grape must spiked with 3-Isobutyl-2-methoxypyrazine (IBMP). Chemical and sensory evaluation of wines arising from MMIPs and MNIPs treatments showed the polymers could effectively decrease green sensory characters without largely compromising overall aroma intensity of the wines, especially when added pre-fermentation. However, this novel and promising technique needs further improvement of the efficiency and specificity of MMIPs before they can be used in a commercial context.
The use of cyclodextrins for enhancement of wine sensory profiles has been trialled for the first time, despite their wide use in the food industry for removal/delivery of flavour compounds and modification of mouth-feel and taste. α-, β-, and γ-cyclodextrins were added to model, white and red wines spiked with volatile phenols associated with smoke taint and Brettanomyces spoilage: guaiacol, 4-methylguaiacol, 4-ethylphenol, 4-ethylguaiacol, ortho-cresol, meta-cresol, para-cresol and eugenol. β-cyclodextrin, with the strongest hydrogen bonding capability, gave the best results in terms of binding volatile phenols. Sensory analysis confirmed a significant reduction in off-flavours after cyclodextrin addition, although some loss of other wine aroma compounds, particularly long chain acids, was also observed. Further work is underway.
Biochemical response of grapevines to smoke exposure
Smoke taint research has largely focused on the chemical and sensory consequences of vineyard exposure to smoke while molecular and biochemical events underlying smoke uptake in berries has received less attention. RNA sequencing of potted Shiraz and Chardonnay grapevines exposed to smoke indicated higher expression of heat shock proteins and glucosyltransferases in smoke affected berries, compared to control berries. Four glucosyltransferases (GT) that yielded higher expression in both varieties and one additional GT that previously showed preferential activity towards smoke derived volatile phenols were selected for further investigation. This study also showed that the volatile phenol glycoconjugate profiles of smoke-affected grapes was variety dependent, with Merlot showing higher levels of glycoconjugates compared to Sauvignon Blanc and Chardonnay. The application of agrichemicals (i.e. kaolin, a particulate clay and Envy, a polymer-based anti-transpirant), prior to smoke exposure did not significantly affect the volatile phenol glycoconjugate profiles in Sauvignon Blanc, Chardonnay and Cabernet Sauvignon, but kaolin provided some protection for Merlot grapes after foliar treatment.
Consumer acceptance of lower alcohol wines
Wine is a very traditional product with high symbolic value, but recent trends in wine consumers’ behaviour support modifying (reducing) alcohol levels, either by partial or complete dealcoholisation. Existing lower/low alcohol wines have not been very successful due to people experiencing these wines as less traditional, less complex and without varietal character. This study examined whether the intrinsic innovation of a product will elicit a stronger influence on perceived authenticity when the product is traditional rather than not traditional. The preliminary exploratory approach towards low alcohol wines, involving twelve focus groups and wine tastings, was conducted in Indonesia, where wine is not a traditional product, Australia, where wine consumption is part of the culture and in France where wine is considered as a very traditional product. Overall results indicated that Indonesian participants are more open to consuming low/no alcohol wine and still consider the product to be wine in contrast to Australian and French participants, who reacted more negatively to the product innovation and did not consider the product to be wine. Quantitative results indicated that traditionality perceptions influence perceptions of authenticity, which in turn significantly influences purchase intention.