Background of the study
Cold stabilisation removes excessive L-tartaric acid natural ionic salts (potassium bitartrate: KHT, and to a lesser extent, calcium tartrate: CaT) from the wine. After fermentation but before bottling, cold stabilisation is routinely carried out to prevent the wine salt KHT from precipitating out of the wine during storage or cooling in the bottle.
Traditional cold stabilisation methods involve cooling the wine to a temperature just above freezing and keeping it at this temperature for weeks or even months. Chilling the wine reduces the solubility of KHT and facilitates its crystallisation and removal through precipitation. During cold storage, precipitation of KHT occurs rapidly in the initial phase and slows down over time as the saturation level of KHT decreases. The temperature and storage time required to stabilise a wine depends on the wine’s composition. Wines with higher sugar and alcohol content require a lower storage temperature than dry wines with 11-12% alcohol. The stability and precipitation of KHT are also influenced by other factors such as the concentration of acids, anions, cations, the pH of the wine, and various complexing agents. To achieve reproducible KHT precipitation, the wine must be clarified and filtered before refrigeration and cold storage. As mentioned, storing wine at near-freezing temperatures is sufficient to remove excess KHT. To prevent the redissolution of the KHT, the wine must also be cold-filtered after cold storage to remove the crystalline KHT precipitate.
Wine stabilisation by cooling is widely used in the wine industry. The process is time-consuming, energy-intensive, and involves a filtration step to remove the sediment. According to the South Australian Wine Industry Association, refrigeration consumes between 50 and 70% of the electricity in a typical winery. Other technical solutions to prevent precipitation of KHT after bottling are reverse osmosis, ion exchange, electrodialysis, and inhibition methods involving additives such as carboxymethyl cellulose (CMC), meta tartaric acid, mannoproteins, or potassium polyaspartate. Processes such as ion exchange and electrodialysis require significant capital investment and considerable expertise to be used effectively. In addition, the cost of water and maintenance can also be high. Tartrate stabilisation has recently focused on the development of compounds capable of inhibiting tartrate crystallisation. However, the possibilities of achieving long-term stability in wines without compromising colour and favourable organoleptic properties are limited. Moreover, the addition of additives in winemaking contradicts the modern trend towards organic and additive-free winemaking envisaged by consumers.
Given these shortcomings of current practices, researchers tried to find a new solution to cold stabilisation, which could be performed at higher temperatures.
Zeolites are hydrated aluminosilicates of sodium, potassium, calcium, or other heteroatoms. These materials are formed naturally by volcanic activity (natural zeolites) but can also be synthesised in the laboratory (synthetic zeolites). Zeolites are extensively used in various technological applications, e.g., as catalysts and molecular sieves, to separate and sort molecules, to dehydrate, to purify water and air, and to remove radioactive contaminants. In this work, researchers explored the potential of zeolites for the cold stabilisation of white wines.
The rationale for applying natural zeolites in cold stabilisation of white wines was based on our previous research and the knowledge that the selective removal of potassium ions from wine down to, i.e., 10–30% of the initial potassium amount, likely inhibits the precipitation of potassium bitartrate salts. The researchers, therefore, hypothesised that natural zeolites could be a material with a promise to be successfully used in the cold stabilisation of white wines.
Effective tartrate stabilisation was achieved by mixing a natural zeolite sample with white wine for three hours. Although the quantum of required zeolite was larger than bentonite, zeolite did not exhibit shrink-swell behaviour, thus enabling greater wine recovery and capacity to be regenerated. Effective heat and cold stability could be achieved using a low-calcium zeolite as a processing aid in a single treatment. To avoid aluminium leaching and elevated aluminium concentrations in the treated wine, the zeolite was calcinated before being added to the wine. The calcination process also reduced calcium content in the wine after treatment with zeolite, thus eliminating the risk of calcium instability. Conclusions. The application of zeolite as a processing aid can potentially be effective in cold-stabilizing white wines and removing proteins responsible for haze formation.
Significance of the study
Zeolites may constitute an alternative technology in white wine production, facilitating heat and cold stabilisation in a single treatment.
Tim Reilly, Pawel Mierczynski, Andri Suwanto, Satriyo Krido Wahono, Waldemar Maniukiewicz, Krasimir Vasilev, Keren Bindon, Agnieszka Mierczynska-Vasilev, “Using Zeolites to Cold Stabilize White Wines”, Australian Journal of Grape and Wine Research, vol. 2023, Article ID 7259974, 12 pages, 2023. https://doi.org/10.1155/2023/7259974
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