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POLYASPARTATE TO AVOID TARTRATE PRECIPITATION
Summary of result obtained in the first project period
Tartrate, an organic acid typical of grapes, combines with potassium and calcium, two cations highly present in grape and then in wine, thus originating crystals that precipitate in the bottle and form an unwelcome deposit for consumers: to avoid this phenomenon, before bottling most wines are treated in order to eliminate the excess of tartaric acid and/or potassium.
According to the most popular technique, the wine is kept refrigerated to temperatures below 0°C for several days, thus inducing the formation and precipitation of crystals in the tank, which are finally eliminated by racking, centrifugation and filtration. This practice represents one of the most important point of energetic consumption in the winery, and has some negative effect on wine sensory profile. Furthermore, many small wineries cannot afford the purchase of the required equipment.
The addition of metatartaric acid can represent an alternative to cold treatment, but limited to wines with short shelf life; other additives, such as carboxymethylcellulose (cellulose gum) and mannoproteins are effective only in wines with low instability, and are not allowed in the production of organic wines (increasing percentage of European wines). The same for electrodialysis and resin exchange, whose development in the wine industry is restraint by the high cost and by the related significant water consumption.
Stabiwine project intends to introduce in the wine industry the use of a new additive, able to inhibit the formation of tartrate crystal, thus preserving the original wine composition. The research is focused on polyaminoacids, and in particular on polyaspartate (PAA), a new anti-scaling additive that is seeing an exponential diffusion in other sectors thanks to their positive combination of efficacy, safety and pricing characteristics. Polyaspartate, obtained by polymerization - through simple heating - of aspartic acid, a widespread aminoacid; the compounds obtained has very high surface charge, and peculiar physical and chemical characteristics which makes it ideal for winemaking use.

The research on polyaminoacids started with a screening of the different types available on the market. Several commercial producers have been contacted and polymers of different nature were tested for their ability to reduce tartrate instability in white and red wines. PAAs resulted better than polyglutammates for this specific application; the tests did not show significant differences among polyaspartates, differing for type of salt, molecular weights and production process. The behavior of best performing PAAs for tartaric stability was studied, to fully understand their interaction with wine component and the overall effect on wine quality.
Several wines - different for type, original, age, degree of tartaric and color instability – were added of variable dose on PAAs, in comparison with most popular additives like metatartaric acid, cellulose gum and arabic gum. Wine parameters were assessed just after addition and, in many cases, after some months of storage.
Meanwhile, polyaspartates underwent several in vitro test to verify the absence of immunological or intestinal effects: all tests showed that PAA is well tolerated. Moreover, PAA is weakly digested by gastric and pancreatic enzymes, thus probably are poorly absorbed into the blood through the intestinal wall. These aspects will be further studied in the next months of the project.
These encouraging results allowed the activation of a series of toxicology tests, in collaboration with a GLP certified laboratory, to scientifically validate the overall safety of the polymer for human health.
The procedure toward authorization of PAA addition for winemaking in Europe was started.

The study led to the identification of a PAA type with many significant advantages on existing additives for tartaric stabilization:
• is effective at low dosage also on very instable wines, both white and red
• over time, is more stable than metatartaric acid
• has lower impact on color stability than cellulose gum
• does not affect wine filtrability
• does not affect color, aroma and taste of wine, even at high dosages
• is easy to solubilize in water and wine

One of the few worldwide producers of commercial polyaspartate was actively involved in the project, and gave a very important contribution to the understanding of the behaviour of polyaspartate in wine by providing samples of different nature, and to the start of the authorization procedure by disclosing key information on production process and quality control.

The project research activity of next months is focused on the characterization of the effects of PAA on wine shelf life: indeed, the chelating properties of the polymer against bivalent cations like iron and cupper is well known in other application. This can potentially reduce the sensitivity of wines to oxidation, thus extending their shelf life or opening new routes for reduction in the use of preservatives like sulphites. Another objective of incoming research on PAA is the study of the interaction of this polymer with macromolecules, both naturally present (proteins, peptides, polyphenols, and polysaccharides coming from grape or fermentation) and added for technological purpose (polysaccharides, proteins, tannins).
Moreover, a large number of applicative trials are planned on different types of wine throughout Europe, in order to observe PAA behavior and potential side effects under real conditions.
There is high confidence that the good characteristics of PAA will be confirmed, and that the new additive could be authorized by EU regulation for winemaking.

The technological, economic and environmental characteristics of PAA are providing very significant advantages on all present practices. Once authorized, tartaric stabilization through addition of PAA is expected to become the first choice for a very large number of wine producers in Europe, especially among small and medium size facilities. Total annual volume of wine treated with PAA can rapidly reach 50 Mhl, with a yearly saving of about 90 M€ and 100 GWh.
Even more relevant, mainly small producers - located in rural areas - will benefit of the resulting increase of competitiveness: therefore, the new technology will also have a notable social impact.



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