ENARTIS NEWS WINE TARTRATE STABILITY The presence of tartrate crystals in a bottle is commonly and alcohol, are concentrated and the precipitation perceived as a fault by consumers. Crystals are mostly that happens is not related to wine concentration composed of potassium bitartrate but precipitation of condition. Furthermore, ice formation damages calcium tartrate is becoming more and more frequent. protective colloids structure that consequently lose While the formation of potassium salts can be their stabilizing effect. For this reason, its use is not prevented with the use of protective colloids, calcium recommended. stabilization requires specific interventions. Potassium bitartrate stabilization There are various methods that can be used during POTASSIUM BITARTRATE the winemaking process to reduce potassium Testing wine potassium tartrate stability bitartrate (KHT) precipitation in bottled wines. Some The Minicontact test (measurement of wine techniques are considered “subtractive” and involve conductivity variation before and after refrigeration reducing the concentration of tartaric acid and/or for 30 minutes with potassium bitartrate seeding) potassium in wine (tank cooling, electrodialysis, and the cold test (6 days storage at -4°C) are quite cation exchange resins). Other “additive” techniques reliable tests for evaluating wine stability. make use of protective colloids or crystallization Wineries that do not have access to the Minicontact inhibitors which can be added to wine. Additive test and that want to save time, often prefer to use techniques are more respectful to sensory qualities the freeze/thaw test (wine is frozen for a few hours and environmentally friendly. However, not all and then thawed before being inspected for any sign permitted protective colloids are effective in the of crystalline tartrate precipitation). This method same way and some of them have specific limits overestimates wine instability. As ice formation under certain circumstances (table 1). occurs, all solutes, including potassium, tartaric acid Table 1: Protective Colloid Characteristics METATARTARIC ACID MANNOPROTEINS CMC POTASSIUM POLYASPARTATE Stabilizing Very good Medium Very good Very good Effectiveness Lasting Stabilizing Effect Scarce Very good Very good Very good Filterability Very good Medium-good * Medium-good * Very good Reactivity with Color None None Yes None Compounds Reactivity with Wine Yes None Yes Yes Proteins *Dependent on CMC degree of polymerization and mannoprotein average molecular weight. Protective colloid stabilizing mechanism crystals are formed. If the dose is too low, inhibition Despite the differences among protective colloids, is only partial and anomalies and unevenness are the stabilizing effect depends on their capability of observed in the shape of the crystals (picture 1). opposing the growth of the nuclei around which Picture 1: Inhibitor colloids interfere with KHT crystal growth. Right: KHT crystal. Left: KHT crystal in presence of CMC. Wine suitability for stabilization with colloids filterability. Once they are homogenously When protective colloids are used for KHT distributed, wine can immediately be bottled. stabilization, wine must meet some requirements: On the contrary, mannoproteins and CMC can decrease wine filterability. CMC effect depends in 1) Protein stability its degree of polymerization (DP): the higher the Metatartaric acid, CMC and potassium polyaspartate DP, the greater the clogging effect. With high DP (KPA), unlike mannoproteins, are quite reactive with CMC, waiting 3-4 days between the addition and wine proteins due to their high negative charge. For final microfiltration helps to bring the filterability this reason, it is imperative to check wine protein index back to acceptable values. Mannoproteins stability and be sure wine is well below the maximum can have very different average molecular weights stability limit, whatever the analytical method used. depending on the method used for their production. Wines close to the stability limit can form haziness or Consequently, they can have a different impact on sediment when metatartaric acid, CMC and/or KPA wine filterability. Information provided by suppliers are added. Preliminary lab addition trials can easily are helpful to understand how to manage filtration. be performed and are very useful for preventing problems and extra labor in the cellar. If haziness CALCIUM TARTRATE appears, bentonite fining is necessary. Testing wine calcium tartrate stability 2) Color stability The main problem with calcium tartrate (CaT) is Color stability is a necessary requirement for all understanding if wine can form precipitate. red wines, regardless of whether they are tartrate Stability tests used to verify KHT stability (cold test stabilized through the use of colloids. and minicontact test) do not confirm if wine is calcium For CMC, it is important to note that it can cause unstable. The reason is that cold temperatures have color precipitation in color stable wines. For this little effect on the rate of CaT precipitation and the reason, the use of CMC in red wines must be always tests are not long enough. In fact, wine calcium combined to the addition of a gum Arabic effective content is very low compared to potassium and this for color stability. The new European Regulation is one of the reasons why the spontaneous formation (EU) N. 2019/934 is going to forbid the use of CMC of nuclei of crystallization can take very long, even in red and rosé wines starting from December 2019. years, making CaT precipitation unpredictable. All the other tartrate stabilizing colloids do not Wine calcium content is the most used parameter stabilize nor destabilize wine color. to classify a wine stable or unstable. For red wines, 60 mg/L is considered the safe maximum limit, for 3) Filterability white wine the limit is 80 mg/L. Wine filterability must be adequate for final filtration. A more reliable test consists of seeding a sample Metatartaric acid and KPA do not change wine of wine with micronized calcium tartrate and stabilization is metatartaric acid. Unfortunately, measuring the quantity of calcium precipitated since it hydrolyzes quickly, its effectiveness is short after 2 days storage at a cold temperature. Calcium and can only be used for wine with a very rapid precipitation above 25 mg/L indicates a high risk of rotation. CaT instability. Alternatively, techniques based on calcium or CaT removal provide a more reliable and long-lasting Calcium tartrate stabilization stability (table 2). The only colloid that has a significant effect for CaT CATION EXCHANGE MICRONIZED CA- COLD STABILITY ELECTRODIALYSIS METATARTARIC ACID D,L-TARTARIC ACID RESINS TARTRATE Ca removal by CaT removal by Stabilizing Removal of Ca; Interference on CaT Precipitation of CaT Removal of Ca formation of Ca seeding nuclei of Mechanism Reduction of pH crystal growth D,L-tartrate crystallization Effectiveness Limited Good Medium Good short-term Very good Very good Uncontrolled Ca Cold temperature has Removal of tartaric Risk of abundant removal; strong Short-term stabilizing Treatment takes 7-10 Limits little effect on CaT acid; lower wine crystal precipitation sensory impact due to effect days precipitation ageing potential over time pH reduction Easy-to-use and Fast and controlled Easy and repectful of Advantages respectful of wine process wine quality quality Table 2: Calcium tartrate This can be achieved by using physical treatments can form kidney stones. or chemicals. Calcium tartrate, and specifically micronized Electrodialysis is the most effective among the calcium tartrate, is used for seeding nuclei of physical treatments, but this technology is not crystallization. In this way, it is unnecessary to wait broadly available to everyone and, by removing for the spontaneous and unpredictable formation tartaric acid and potassium, it has an impact on of nuclei, while at the same time promoting a rapid wine sensory qualities and ageing potential. formation and precipitation of crystals. Because of Cation exchange resins help reduce calcium content, the insolubility of calcium tartrate, treatment can but their effectiveness on CaT stability is mainly due be done at cellar temperature, (10-15°C), avoiding to their action of lowering wine pH. Unfortunately, cooling. Crystal precipitation takes approximately the lowering of pH is not always organoleptically 7-10 days and guarantees wine stability without pleasing. impacting wine sensory. Cold stability is not a reliable technique. Low Since CaT precipitation induces KHT precipitation temperatures do not significantly increase or and not the other way around, it is more convenient accelerate CaT precipitation and the usual 7-14 days to start stabilizing calcium first then potassium cooling treatment can be too short. (picture 2). Calcium tartrate and D,L-tartaric acid are the only chemicals permitted by the OIV for CaT stabilization. Evaluation of D,L-tartaric acid effectiveness is supposed to CaT stability depend on its capability to form a calcium salt CaT stable CaT unstable that is much more insoluble than the one formed by the L-tartaric acid naturally present in wine. In Evaluation of Stabilization with reality, this characteristic is not enough to make KHT stability Enocristal Ca D,L-tartaric acid a reliable stabilizer. The formation of nuclei starting the crystallization process takes KHT stable KHT unstable a long time and, because of the high insolubility of calcium D,L-tartrate, its application can easily