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g WINE g rAoKw i n g rape M ING PART TWO Bitartrate and Tartrate Stability Red wine crystals are viewed at 20x magnification (courtesy of ETS Laboratories). Understanding and evaluating cellar and laboratory methods BY Patricia Howe C '' old stability," as defined by the individual winery or winemaker, is achieved through cellar treatments. These treatments utilize aspects of the chemistry and physics discussed in Part I (Winter 2013 PWV Journal) to manipulate the formation of potassium bitartrate crystals. Calcium tartrate crystal formation may also be affected by these techniques, but this salt requires more time to precipitate and is less affected by cold temperature methods. Stability with respect to both the potassium and the calcium salts is necessary to achieve crystal-free wines. Several types of laboratory testing methods are used to evaluate the efficacy of the cellar treatments. Each cold stability laboratory test is empirical; every test is a predictive index of stability, not actual measures of stability. This limitation does not reduce their utility. The various cellar treatments and laboratory tests use one or more of five aspects of impacting crystallization discussed in Part I. These are summarized simply as: 1) ionic concentration and complexing, 2) crystal formation and melting, 3) optimization of concentration and time, 4) diffusion, and 5) fouling. By providing categorization of the various cellar and laboratory methods, and by discussing the issues involved in each method, we hope to provide common language to make any discussions about issues of "cold stability" more precise and productive. Cellar practices for cold stabilizing wines Each cellar treatment has different demands on staff, energy, equipment and time. Further, each method has different potentials for quality risk due to oxidation, changes in acid balance or other sensory factors. Allowed processes and treatments for wine are listed in the U.S. Federal Register 27 CFR 24.246 and 27 CFR 24.248 and should be consulted before using any treatment or process. New materials and processes, if they meet the standard of "good industry practice" and follow the TTB approval process, may also be considered for limited industry use. For example, some mannoproteins and carboxymethylcelluloses have been through the initial process and wineries may use them if proper paperwork is filed. TTB rules are elaborated at their website and should be consulted (ttb.gov/wine/wine_treating_materials.shtml). Cellar treatments focus on reducing the concentration of potassium tartrate (and calcium) by precipitation or other means, or on increasing the macromolecular chemical complexing of these ions and increasing the crystal fouling (the inhibition of the growth of the crystal via stearic or ionic hindrance). The methods listed reflect the current range and observed trends of stabilization methods. A. Passive cold holding — exposing wines to natural cold weather extremes from winter weather, with no inputs, generally followed by separation of wine from precipitated crystals. This method relies solely on the effect of temperature to induce possible crystal nucleation and precipitation, resulting in a decrease in the concentration of the ionic species. The ability for the salts to nucleate will be dependent on the concentration being high enough or on the existence of other nucleation sites (such as solid particles, ice or rough surfaces). This passive method expresses no control over the time and temperature exposures. B. Active cold holding with inputs — refrigeration at a set or chosen temperature, with or without ice crystal formation or addition of cream of tartar (powdered or crystallized potassium bitartrate, i.e. Cellar Treatment Category I: Ionic species reduction by precipitation methods These cellar treatments use the precipitation of the salt crystals to reduce concentration of potassium (and calcium) cations and the bitartrate anion. Efficacy is increased when the crystallization is optimized through appropriate inputs. Typical cellar scene: A tank undergoes chilling in a relatively passive attempt to achieve cold stability. pr actica l win ery & vin eya rd APRIL 20 13 55