Managing wine extraction, retention, clarity and stability for defined styles and efficient production
Abstract
This project provided fundamental knowledge and practical approaches to manage the extraction and stability of wine macromolecules. Key areas addressed were protein stability, cold stability and maceration techniques. New techniques for wine macromolecule analysis were developed and alternative approaches to stabilisation were demonstrated. Natural zeolites can confer both protein and cold stability in a single application. Protein and cold stability could be achieved using plasma polymerised coatings, applied as nanoparticles or functionalised surfaces. Monomeric anthocyanin was found to significantly inhibit tartrate crystallisation, while polysaccharides did not. Red wine maceration approaches were studied, identifying levers to modify wine phenolic composition and style.
Summary
The key stakeholders in this project are wine producers. At the outset of the project, its goal was to generate new knowledge and tools to allow winemakers to more objectively manage and improve extraction processes and address stability, clarity, filterability and production efficiency issues during winemaking.
Alternative strategies for achieving protein stability and cold stability were evaluated, deploying novel additives or processing techniques. Regeneration protocols were developed for magnetic nanoparticles (MNPs), previously shown to successfully remove haze-forming proteins. MNPs could be regenerated and reused with a water wash, which would be a low-cost process.
For the first time, natural zeolites were shown to have dual functionality to heat- and cold-stabilise white wines in a single treatment. This could have a positive impact on wine production in terms of cost and energy efficiency. Importantly, compared to bentonites, zeolites cause much less wine loss and can be potentially reused as soil amendments in agriculture. Zeolites could also be completely regenerated through electrochemical methods or simply by treatment with salt solution (10%). Further research is needed to understand potential aroma scalping or deposition of aluminium before regulatory approval is sought.
A further alternative cold stabilisation approach was implemented, which harnessed the use of plasma-polymerised surfaces for the first time. In this work, the ability of plasma-polymerised surfaces to bind potassium bitartrate (KHT) through electrostatic interactions was used to initiate and progress crystallisation at the functionalised surface. After crystallisation was complete, the surface could be removed from the wine and regenerated. Importantly, this approach was found to be effective for different white wine samples at both lower and cellar temperatures. This work has therefore shown the promising potential for cold stabilisation to be conducted more sustainably, without the need for a chilling step.
A further area of research aimed to better support the management of cold stabilisation by being able to more effectively predict if it will occur. A new method to assess cold stability was developed which uses KHT crystal recovery and quantification following a three-day cold test. Using this, and other traditional analytical approaches, it was found for white wine that lower wine tartaric acid and high potassium largely explained KHT crystal formation, and cold stability was not clearly influenced by macromolecules such as polysaccharides, proteins and phenolics. This led to the conclusion that for the development of more cost-effective and sustainable approaches to white wine cold stabilisation, potassium removal needs to be considered as a primary strategy. For red wines, it was found that monomeric, ionised anthocyanins were able to confer cold stability at even low concentrations (250 mg/L), while as for white wine, other macromolecules had little, or no influence. This indicates that the maintenance of a fraction of ionised anthocyanins in red wines may be able to confer protection against KHT crystallisation, but more knowledge is required to better control pigment conversion and loss during wine processing and ageing.
Work on macromolecule extraction, retention and stability continued in this project. A number of new analytical methods were developed, validated and implemented in wine matrices. A rapid fluorescence-based method to detect haze-forming proteins in white wines was developed. The method is selective for haze-forming proteins, providing a linear detection range and with a low detection limit. It offers winemakers an alternative to the commonly used heat test, and could offer faster, cheaper and more accurate screening of protein-unstable white wines. Noting that in certain grape cultivars, protein can cause tannin loss, a new method for measuring red wine protein was validated. A study was undertaken to attempt to decouple protein-tannin interactions during fermentation by using a proteolytic enzyme (proctase). It was found that adding proctase alone could increase tannin extraction, but did not alter protein concentration. This could be a simple approach to enhance tannin extraction in low phenolic cultivars, sites or regions.
A range of methods for the study of wine colloids and macromolecular interactions were applied in this project. A pioneering study aimed to monitor the interactions between wine proteins, polysaccharides and tannins using fluorescence correlation spectroscopy (FCS). The study provided strong experimental evidence that macromolecular interactions could be characterised with FCS. Other techniques such as nanoparticle tracking analysis (NTA) and isothermal titration calorimetry (ITC) were also applied in this project when required to characterise wine macromolecular interactions. A key outcome was to show that wine acetaldehyde may react to form unstable adducts between tannin and anthocyanin. NTA revealed that these unstable pigments undergo extensive aggregation before precipitating. Further research should seek to understand the extent of acetaldehyde-mediated precipitation and loss of pigments during fermentation, in particular in aerated ferments.
Three AWRI-led trials were completed which investigated outcomes of maceration techniques on macromolecule extraction and retention in red winemaking. A study was undertaken on water addition to Shiraz musts, which showed that although losses in phenolics could be expected with water addition, it was nonetheless an effective way to manage high sugar concentrations associated with very ripe fruit.
A second trial studied whole bunch fermentation in Pinot Noir and Shiraz, with whole bunch inclusions ranging from 25% to 100% relative to crushed fruit. For Pinot Noir, differences in phenolic extraction with whole bunch inclusion were minor, with greater effects observed for aroma and flavour (reported in the Final Report for Project 3.1.1). For Shiraz, increases in extraction of tannin from stems with whole bunch inclusion were substantial, and improvements in colour were found even with the lowest level of whole bunch addition. Whole bunch inclusion also increased wine astringency. Although a small level of whole bunch inclusion showed some benefits for tannin extraction and colour improvement in Shiraz, a cautionary approach to including higher levels of whole bunches in ferments is advised, due to the introduction of harsh astringency and ‘green capsicum’ attributes.
A final maceration trial aimed to investigate the relative impact of maceration time and the use of Della Toffola’s maceration accelerator (DTMA) on wine phenolics. A further objective was to understand the importance of grape ‘phenolic potential’ on maceration outcomes. Vineyard phenolics were monitored by comparing the trend in total and extractable tannin and colour in grapes during ripening, showing for the first time that extractable tannin and colour consistently increased. The application of DTMA to high- and low-phenolic grapes showed that DTMA with a short (four day) maceration increased tannin extraction for both grape batches. However, as maceration time was extended, the DTMA-treated ferments from the high-phenolic grape batch were not different from the control, while for the low-phenolic musts, DTMA enhanced both tannin and colour. These measures were improved relative to both the control and DTMA treatments of the high-phenolic grapes, a remarkable outcome. Based on these findings, the DTMA technique holds the potential to improve phenolic outcomes in low phenolic varieties, or regions that may struggle to meet optimal grape colour or tannin targets, such as warm, irrigated regions.