Non-subtractive approach to potassium tartrate stabilization.
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 contamination--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 material at the bottom of the bottle.
Precipitates are clearly seen as flaws in wine--both by educated and non-educated consumers--therefore winemakers may need to address this as a priority during the winemaking process.
Traditional and modern tartrate stabilization methods do exist, but they do not always meet all of the demand criteria listed above. Development of novel inhibitory methods for potassium bitartrate stabilization of wines has led to the commercialization of two revolutionary non-subtractive methods for stabilization: addition of carboxymethyl cellulose (CMC) reported in this article, and addition 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 reaction 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 Recognized 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 equilibrium with counter ions, but only the bitartrate form can produce crystals. Tartrate instability in wine comes from two salts of bitartrate: potassium (KHT) and calcium (CaHT). The formation of KHT crystals depends upon many factors including 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 impurities present in the wine where KHT aggregation and crystallization can initiate. 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 instability), 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 instability 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 selective removal of the potassium and tartrate ions, therefore rendering the resultant wine stable to KHT precipitation. By
lowering and holding the wine temperature to slightly below freezing (32[degrees] 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 drawbacks. It does not always prevent subsequent tartrate precipitations due to wine matrix effects along with wine exposure to temperatures below that of the stabilization treatment. Standard cold stabilization can be inefficient in terms of both energy and time leading to excessive cost. Cellar and laboratory labor investments can be considerable in traditional application of cold stabilization procedures and iterative testing.
Changes in wine character through removal of ion components can also be significant, such as a pH shift that can result in imbalances that must be corrected in the winery before bottling. During conventional cold stabilization there is a potential for extract reduction, thus lowering the perception of wine body.
In addition to traditional cold stabilizing methods, another subtractive technique has been introduced to the winemaking industry: electrodialysis. In electrodialysis, ion-selective membranes are utilized to lower the potassium, calcium and tartaric acid concentrations to levels determined by pretreatment testing that should result in stabilization of the wine against KHT and CaHT precipitation events.
The replacement of temperature reduction of the target wine allows for a significant reduction in energy input to the stabilization process. Electrodialysis, however, can require a sizable capital investment, exhibit limited throughput and have significant water-use requirements. The benefits and obstacles of electrodialysis have been discussed in many prior publications. (10) (Practical Winery & Vineyard, Sept./Oct. 2008, Jan./Feb. 2004.)
Innovative non-subtractive technologies for tartrate stabilization
Since their discovery and introduction into the EU market, carbohydrate polymers with tartrate crystal inhibitory properties have shown great utility and benefit. With the 2006 EU introduction of a specific mannoprotein MP40, (5) which inhibits bitartrate nucleation in a non subtractive manner, a new paradigm was established for KHT stabilization.
Following the specific mannoprotein MP40, another polymer, carboxymethyl cellulose (CMC), was introduced in the EU in 2008. CMC provides protection from KHT precipitation by inhibiting the growth of KHT crystals. Since their initial discovery, these innovative technologies have been introduced, accepted and approved around the world in every major winegrowing region, and following the 2012 U.S. introduction they are now entering the final stage of TTB regulatory approval. (4)
Application of the mannoprotein and CMC differ with mannoprotein being appropriate for use in all wines--red, white and rose--within instructional guidelines and use criteria, while CMC is recommended for all white wines and most rose wines depending upon any interactions with color material in the wine. In white wine applications, CMC has been shown to be effective 100% of the time when pretreatment criteria and application guidelines are followed.
Rose wines can be slightly more challenging with the complication being interaction with unstable color compounds; around 80%-85% of rose wines are suitable for CMC application, so trials at the bench-scale should be done before full treatment. Investigation of the use of two different CMCs for KHT stabilization in comparison to metatartaric acid and gum arabic in both Chardonnay and Pinot Blanc illustrated the utility of specific CMC in achieving KHT stability. (3)
Lab validation of tartrate stabilization
Initial determination of the tartrate stability status of a wine can be estimated through current test methods such as standard University of California, Davis (UC Davis), conductivity testing, concentration product testing or Stabilab DIT analysis, although the percent instability values given by UC Davis conductivity and DIT are preferred for interpretation of the applicability and dosage of non-subtractive methods for tartrate stabilization.
Since non-subtractive tartrate stabilization methods do not physically remove potassium ions or tartrate molecules from the wine as a result of treatment, the use of traditional test methods for tartrate stability after treatment tend to give false negative results.
A specific method, the ISTC50 that assays the effectiveness of non-subtractive stabilization treatments, was developed by Eurodia for the Stabilab instrument that is based upon conductivity change under the conditions of the modified test. Both the DIT and ISTC-50 are rapid tests with results usually available on a next-day basis.
An alternative test is the OIV-certified cold test that consists of freezing a sample at a consistent temperature of -4[degrees] C for six days and assaying the KHT crystal status of the sample. This test relies upon a dedicated -4[degrees] C freezer that is constant temperature (not frost-free) and a lengthy waiting period, both of which bring a level of inconvenience to the testing process.
What is CMC and what properties are important for proper performance?
CMC has been used for many years in a multitude of everyday food products where it serves as a stabilizer, emulsifier and thickening agent in diverse products such as ice cream, cake and batter mixes, frostings, pie fillings and toothpaste to name a few.
CMC is produced under controlled chemical conditions to yield a specific degree of polymerization (DP) and degree of substitution (DS) characteristics. These physical measures, DP and DS, determine many of the properties of CMC that make it so useful in KHT stabilization.
The degree of polymerization of CMC influences the physical characteristics of the molecule in solution such as viscosity and fluidity. In terms of mixing, we recommend to dilute the liquid CMC in twice its volume of wine. (This can vary from one supplier to another as CMC concentration does vary greatly from one product to another.) Mixing of the tank through a pump over of 1.5 to two times the tank volume is recommended.
The degree of substitution along the cellulose polymer of CMC influences many of the functional properties including: solubility of the CMC in water and wine, efficiency of the CMC in inhibiting KHT crystal growth as explained below and determination of the extent of interactions with other wine matrix components that may be detrimental to the proper functioning of CMC in wine.
The negatively charged CMC polymer interacts with the nascent crystal surface and prevents further growth (Figure 5). No potassium or tartaric acid is removed, thus preserving the wine's natural balance, but crystallization is inhibited so no precipitates form in the treated wine.
How does CMC actually work to inhibit KHT crystal growth? In Figure 3 an illustration of the size differential between a hydrogen atom and a potassium atom shows that potassium is much larger. In the crystal structures imagine KHT molecules aligned in an end to end fashion, all lying nice and compact and flat at the crystal surface. The potassium molecules would be sticking up above the profile of the tartrate layer due to the larger diameter; this would act like a series of positively charged bumps all along the crystalline molecular surface.
The attraction between the negatively charged CMC and the positive charges on the KHT crystal surface acts like Velcro, with a multitude of ionic interactions driving an association that is effectively permanent--in fact wine treated with CMC can exhibit long-term stability. (14)
In addition to the physical performance properties that the DP and DS lend to CMC, physical properties that allow for low effective usage rates (100 ppm) and stability to temperature extremes need to be considered in product development. Purity of the CMC is important in respect to elimination of degradation that results in heterogeneity of molecular size and negative impact on performance. Refining of CMC to remove excess sodium after the initial production is important because sodium can impact the organoleptic qualities of a wine.
In development of a CMC product for use in wine tartrate stability treatment, parameters such as product color, chemical impacts and organoleptic influence need to be considered. Since CMC is recommended for white and rose wines, there should be no increase in A420 of white wines. Some less pure CMC can have a yellow color that is transferred to the wine upon treatment.
The purpose of CMC treatment is not to modify the wine chemistry but simply provide KHT stability. Measurements of S02, total acidity, pH, volatile acidity, ethanol, NTU and color should all remain unchanged, thus preserving the wine balance intended by the winemaker.
Organoleptic impacts from CMC use should be undetectable. These potential impacts include color changes, modification of flavor-aroma profile and impacts on body, weight or mouthfeel of the treated wines, all of which can affect the perception of the wines. In specific trial applications, comparison of available tartrate stabilization methods showed differences in chemical effects and organoleptic impacts.
Not all CMC is the same in regard to DP, DS and functionality. As indicated by the diverse uses for CMC in many different food applications, the physical properties of CMC can be altered through structural differences created by specific production processes or refinement steps. Proper attention to the production and purification of the CMC raw material, followed by appropriate product formulation and handling, should alleviate concerns. Ask your supplier for details.
The many different properties and applications of CMC are explained in depth at: codexalimentarius.net/gsfaonline/additives/details.html?id=51 and at en.wikipedia.org/wiki/Carboxymethyl_cellulose.
How is CMC integrated into cellar practices?
CMC should be dosed at 100 ppm of pure carboxymethyl cellulose: check the CMC concentration for the product you are using and calculate the dose appropriately. The CMC should be diluted in two times the dose volume of wine and then thoroughly blended with the total volume of wine to be treated. The CMC addition should be at least 48 hours before final filtration and bottling to avoid any adverse filtration effects.
CMC should be the last treatment to the wine before bottling. Any additions or treatments that could affect the colloidal stability of the wine should be avoided. Additions that are compatible with or after CMC addition include: sulfur dioxide, gum arabic, carbon dioxide and ascorbate. All other additions including acid, sugar/concentrate or wine blending should be avoided.
Use of CMC as a non-subtractive tartrate stabilization agent creates an entirely new paradigm in wine processing. However the addition of CMC is not a simple plug and play substitute for traditional cold stabilization; the evaluation criteria for CMC use and the timing of operations are different.
While traditional cold stabilization is a cellar process performed sometime between the end of fermentation and bottling, CMC KHT stabilization should be thought of as the last treatment of the wine before bottling. CMC use criteria include wine protein/heat stability and involve caution for lysozyme-treated wines that should be bench-trialed for CMC compatibility. Excess proteins in unstable wine can interact with the negatively charged CMC and may result in a haze formation in the treated wine.
The initial tartrate instability of the wine should be below 30% by DIT or the UC Davis conductivity testing. Wines should be clean and well-clarified before CMC addition, a clogging index filterability measurement below 30 and an NTU reading below 4.0 for white wines and below 6.0 for rose wines is recommended with pre-filtration highly recommended.
Temperature of the wine should be greater than -15[degrees] C (59[degrees] F) before CMC addition and throughout final filtration and bottling to ensure normal wine viscosity and an easy filtration. Pressure at bottling should remain below 0.8 bar, which would indicate that there is no blocking of the filter that could retain some of the CMC, potentially impacting the final effective concentration of CMC in the finished wine.
Calcium is another use-criteria consideration. Because CMC protects only against KHT instability, calcium levels should be below 80 ppm to minimize the risk of CaHT crystal formation. Wine deacidification with calcium carbonate or specific vineyard soil and rootstock effects can result in high calcium levels in must and wine.
It is best to check the incoming must for calcium content as treatments exist for lowering initial calcium content very early in must/juice treatment or during fermentation, creating compatibility with CMC for later stabilization application.
Case studies and results of CMC addition
CMC is a robust treatment method to achieve KHT stabilization.
Applications of CMC for KHT stabilization in major North American white wine varieties such as Chardonnay, Sauvignon Blanc, Pinot Gris, Riesling, Gewurtztraminer, Chenin Blanc and numerous white wine blends and diverse varieties have all proven effective. Since the introduction of CMC into the U.S. market in 2012, more than 2 million gallons of wines with diverse instability have been successfully treated.
A collaborative study between UC Davis and Laffort USA on tartrate stability was conducted at the UC Davis teaching and research winery. Traditional cold stabilization was compared to the addition of carboxymethyl cellulose (CMC at 100 ppm, Celstab) to obtain tartrate stability. Two different white wines, a Sauvignon Blanc (pH 3.31, TA 7.9 g/L, 12.4% ethanol) and a Chardonnay (pH 3.71, TA 6.1 g/L, 14.2% ethanol) were included in the bench trial study.
Both the Chardonnay and Sauvignon Blanc wines were determined to be tartrate-unstable using the standard UC Davis conductivity test. The wines were proteinstabilized to a heat-test turbidity reading of less than 2 NTU before undergoing respective tartrate-stabilization treatments.
Quadruplicate samples of each wine were treated with 100 ppm of CMC (1,000 ppm of Celstab) or cold stabilized at a constant temperature of 25[degrees] F. Both the Sauvignon Blanc and the Chardonnay achieved immediate tartrate stability when treated with CMC, where as the wines that were cold stabilized at 25[degrees] F took between eight and 10 weeks to achieve tartrate stability as determined by ISTC-50 testing.
All wine samples for both the CMC and cold stabilization were still tartratestable after 22 months of bottle aging as determined by ISTC-50 testing.
In a specific commercial winery trial application, tartrate-stabilization treatments including traditional cold stabilization, electrodialysis and CMC addition were compared relative to chemical alteration of the wine for parameters including alcohol, pH, TA, free and total S02 and sensory evaluation preference testing. Results showed that CMC had the lowest impact on chemical parameters of the wine and was significantly preferred in tasting evaluations (Figure 7a and 7b).
In a scientific study of an analytical method to detect CMC in finished wine, sensory evaluation by a 20-member expert panel detected no significant effect on wine perception at the legal dose of 100 ppm. Further sensory experiments showed that at up to 15 times the maximum dose of a particular CMC there was no significant impact on taste or aroma perception of the treated wine. (9)
Traditional cold stabilization methods to achieve KHT stability in wines involve considerable capital infrastructure for chilling systems that can involve safety risks and maintenance costs in addition to a very significant energy cost to operate. Cold stabilization can be time-consuming, unpredictable, labor-intensive in both set up and clean up after stabilization with water resource costs as well.
In addition, the wine chemical composition alterations that occur during the cold stabilization process can alter the sensory perception of a wine. While electrodialysis saves a good deal of energy compared to traditional cold stabilization, it can also incur some of the same drawbacks of cold stabilization such as capital costs, specialized operations training, wine chemistry alteration and water use. Electrodialysis is also limited in throughput.
Paradigm-changing non-subtractive technologies such as CMC addition to achieve KHT stability in wines present many tangible benefits while overcoming many burdens of subtractive technologies. Initial acceptance of new technologies is a slow process, yet in the short time CMC has been available on the world market use has increased ex ponentially each year.
The benefits of CMC addition for KHT stabilization are varied and plentiful. From economic and environmental improvements to ease of use and wine quality advancement, every wine producer can benefit from CMC adoption.
Elimination of cold stabilization has been documented to save considerable energy as shown quantitatively in the joint PG&E industry study by Steve Fok. (10) Based upon PG&E measurements using methods other than chilling, 80% or more energy can be saved. Since chiller operation can be a significant cost to a winery, this is a large and meaningful economic benefit. Estimates of $0.25 per gallon energy cost for cold stabilizing a wine can be reduced to $0,045 per gallon with CMC use.
The reduction in cellar labor, water, maintenance along with no capital investment to begin CMC implementation -- adds to the economic benefits. With non-subtractive methods like CMC there are no lees to recover wine from, which yields financial gains. Environmental benefits begin with energy and water savings and add up to a reduction in waste processing and a reduced carbon footprint in the winery.
CMC is easy to use and efficient; a small dose provides long-term stability while putting process control in the hands of the winemaker with a predictable timeline for application and effectiveness and minimal laboratory testing. CMC liquid products are formulated for easy addition to wine and could be readily automated to further improve cellar logistics while eliminating time and labor-intensive tartrate removal from stabilization tanks.
Predictable control allows for alignment with cellar logistics and bottling demands. Maintaining wine chemistry and acid balance leads to organoleptic preference for wines treated with CMC compared to other KHT stabilization methods.
Thanks to the early adopters in the U.S. wine industry, the rapid movement through the regulatory system in the U.S. has poised both CMC and mannoprotein on the verge of final approval from TTB, allowing the U.S. to join the other major wine-producing regions in the world in adoption of these new paradigm changing non-subtractive KHT stabilization technologies.
Caption: Figure 1. Array of wine and carboxymethyl cellulose characteristics. The color, size and weight of type represent the category, importance and timing.
Caption: 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.
Caption: Figure 3. The chemical reaction process for sodium carboxymethyl cellulose (Na-CMC) production by treating the glucose polymer cellulose with chloroacetic acid under basic conditions.4
Caption: Figure 4. Plot of KHT solubility versus temperature showing solubility and hypersolubility curves with resultant partitioning of KHT crystallization.12
Caption: Figure 5. Molecular structure of sodium carboxymethyl cellulose. Carboxymethyl group pKa of 4.0 indicates that the groups will be negatively charged at wine pH. (Modified from London South Bank University web page: lsbu.ac.uk/water/hycmc.html.)
Caption: Figure 6. Size differential between hydrogen (H+) and potassium (K+) atoms (left).'5 Impact of carboxymethyl cellulos-KHT+ crystal surface interaction on KHT crystal size and shape (right).
Caption: Figure 7a. Spider graphs representing two different white wine blends illustrate chemical changes incurred by traditional cold stabilization, electrodialysis and carboxymethyl cellulose treatment.
Caption: Figure 7b. The bar graph shows winemaker preference for carboxymethyl cellulosetreated wines.
(1.) Berg, H.W. and R.M. Keefer. 1958 "Analytical determination of tartrate stability in wine 1. Potassium bitartrate." Am. J. Enol. & Vit. Vol. 9.
(2.) Berg, H.W. and M. Akyoshi. 1971 "The utility of potassium bitartrate concentration product values in wine processing." Am. J. Enol. & Vit. Vol. 22, No. 3.
(3.) Bosso, A., et al. 2010 "The use of carboxymethylcellulose for the tartaric stabilization of white wines, in comparison with other enological additives." Vitis, Vol. 49, No. 2.
(4.) Boyer, P., et al. 2010 "CMC: a new potassium bitartrate stabilization tool." Australian & New Zealand Grapegrower & Winemaker, Issue 558, July.
(5.) Dubourdieu, D. and V. Moine. 2000 "Biological substance for the physic-chemical stabilization of wines." U.S. Patent No. 6,139,891, Oct. 31.
(6.) Pilone, B.F. and H.W. Berg. 1965 "Some factors affecting tartrate stability in wine." Am. J. Enol. & Vit. Vol. 16.
(7.) Rhein, O. and F. Neradt. 1979 "Tartrate stabilization by the contact process. Am. J. Enol. & Vit. Vol. 30, No. 4.
(8.) Palma, M. and C. Barroso. 2004 "Acid-Base and Precipitation Equilibria in Wine." J. of Chem. Edu., Vol. 81, No. 1.
(9.) Salagoity, M-H., et al. 2011 "Quantification Method and Organoleptic Impact of Added Carboxymethyl Cellulose to Dry White Wine." Anal. Methods, Vol. 3.
(10.) Fok, S. 2008 "PG&E Studies Electrodialysis for Cold Stability." Practical Winery & Vineyard, Sept./Oct.
(11.) Howe, P. 2013 "Cold Stability of Wine: Potassium Bitartrate, Calcium Tartrate." Practical Winery & Vineyard, Winter.
(12.) Boulton, R., et al. 1996 Principles and Practices of Winemaking, New York: Chapman and Hall.
(13.) Howe, P. 2013 "Cold Stability of Wine: Understanding and Evaluating Cellar and Laboratory Methods." Practical Winery & Vineyard, April.
(14.) Du Toit, W.J. et al. 2013 "Short- and long-term efficiency of carboxymethylcellulose (CMC) to prevent crystal formation in South African wine" Food Additives and Contaminants: Part A--Chemistry, Analysis, Control, Exposure and Risk Assessment 29(9).
(15.) Bentor, Y. Chemical Element.com--Potassium, Hydrogen. Dec. 5, 2013 chemicalelements.com/elements/k.html.
Peter Salamone PhD, Laffort USA, Petaluma, Calif., and Anita Oberholster PhD, Department of Viticulture & Enology, University of California, Davis, Calif.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Title Annotation:||CARBOXYMETHYL CELLULOSE--CMC|
|Comment:||Non-subtractive approach to potassium tartrate stabilization.(CARBOXYMETHYL CELLULOSE--CMC)|
|Author:||Salamone, Peter; Oberholster, Anita|
|Publication:||Wines & Vines|
|Date:||Feb 1, 2015|
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