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February 2015 practical winery & vineyard 67 w i n e m a k i n g Non-subtractive approach to potassium tartrate stabilization W inemakers today are under in creasing pressure to get tartrate-stable wines into the marketplace rapidly while considering complicating factors such as method effectiveness, cost impact, energy efficiency and production/bottling logistics. Consumer preference surveys have shown that precipitates in wine are often viewed unfavorably and can be thought of as flaws in the wine — or even con- tamination — since tartrate crystals can resemble glass shards in the bottle. In a survey conducted for the Laffort Co. of more than 2,000 wine consumers in the United States, 50% of U.S. wine consumers see any in-bottle precipitate as negative. Forty percent would not buy a wine again that has a precipitate, and 30% of U.S. wine consumers understand the origin of precipitate but still would not buy a wine again if it showed mate- rial at the bottom of the bottle. Precipitates are clearly seen as flaws in wine — both by educated and non-edu- cated consumers — therefore winemak- ers may need to address this as a priority during the winemaking process. Traditional and modern tartrate sta- bilization methods do exist, but they do not always meet all of the demand cri- teria listed above. Development of novel inhibitory methods for potassium bitar- trate stabilization of wines has led to the commercialization of two revolutionary non-subtractive methods for stabiliza- tion: addition of carboxymethyl cellulose (CMC) reported in this article, and addi- tion of a specific mannoprotein that will be the subject of a future article. The continuing search for solutions has led to development of novel methods for tartrate stabilization. Before we explore what the newest solutions offer, let's look at some fundamentals. CMC is the product of the chemical re- action of cellulose with chloroacetic acid under basic conditions (Figure 3). While the cellulose is derived from wood, the subsequent substitution reaction and conditions, while GRAS (Generally Rec- ognized as Safe) under Food and Drug Administration rules, eliminate it from use in wines labeled as natural or organic by their organizational guidelines. Tartaric acid in wine exists in equi- librium with counter ions, but only the bitartrate form can produce crystals. Tar- trate instability in wine comes from two salts of bitartrate: potassium (KHT) and calcium (CaHT). The formation of KHT crystals depends upon many factors in- cluding the concentration of tartrate and potassium molecules, alcohol level, pH and temperature of the wine and other wine matrix effects. 1 Nucleation sites include cork and bottle surface imperfections or particulate im- purities present in the wine where KHT aggregation and crystallization can initi- ate. KHT crystal growth can be affected by the presence of protective colloids such as polysaccharides, proteins, tannins/ polyphenolics and even sulfates. 11 Tartrate stability: fact or fiction? Measurements of different molecular concentrations and/or physical changes in wines over time form the basis for the evaluation of the tartrate stability of wines in production. Methods such as the potassium concentration product, electrical conductivity, mini-contact, DIT Stabilab (degree of initial tartrate insta- bility), ISTC-50 Stabilab and freeze test all provide information concerning the state of wine in relation to the probability of tartrate deposits forming. No single test provides a clear yes or no answer to the question of tartrate stability. Risk assessment and pass-fail criteria are still the realm of individual winemaker decision making. Tartrate in- stability remains one of the key potential instabilities in all wines. 2,6,7,12,13 Subtractive methods for tartrate stabilization The question of how to achieve tartrate stabilization has been addressed by selec- tive removal of the potassium and tartrate ions, therefore rendering the resultant wine stable to KHT precipitation. By low- ering and holding the wine temperature to slightly below freezing (32º F), the solubility of KHT is driven through the supersaturation phase resulting in KHT crystal formation allowing for stability of subsequent precipitation events to be far less likely (Figure 4). Cold stabilization can have its draw- backs. It does not always prevent subse- quent tartrate precipitations due to wine matrix effects along with wine exposure to temperatures below that of the stabi- lization treatment. Standard cold stabili- zation can be inefficient in terms of both energy and time leading to excessive cost. Cellar and laboratory labor invest- ments can be considerable in traditional application of cold stabilization proce- dures and iterative testing. Changes in wine character through re- moval of ion components can also be sig- nificant, such as a pH shift that can result in imbalances that must be corrected in the winery before bottling. During con- ventional cold stabilization there is a po- tential for extract reduction, thus lowering the perception of wine body. In addition to traditional cold sta- Carboxymethyl Cellulose – CmC Peter Salamone PhD, Laffort USA, Petaluma, Calif., and Anita Oberholster PhD, Department of Viticulture & Enology, University of California, Davis, Calif. BY Figure 2. equilibrium of hydrogen and potassium counter ions with the dicarboxylic molecule of tartaric acid. the mono-substituted potassium bitartrate may form crystal structures. Viscosity C a l c i u m C o n c e n t r a t i o n Timing Filterability Fluidity Instability Turbidity Filtration Eicacy Purity Figure 1. array of wine and carboxymethyl cellulose characteristics. the color, size and weight of type represent the category, importance and timing.