average number of glucopyranose units per polymer molecule. This mean number indicates that a given CMC, like metatartaric acid, is a polymer with a range of molecular weights.
A DS of 0.65 means that, out of 100 glucopyranose units, 65 have been etherified by sodium chloroacetate in a basic medium, as shown in the reaction diagram (Figure 1.24).
The DP determines the viscosity of a CMC. Viscosity increases with molecular weight. It also varies according to the cation: divalent cations (calcium, magnesium, iron, etc.) reduce viscosity. The DP determines the molecular weight, which may vary from 17,000 to 1,500,000 Da.
For a CMC with a given DP, the higher its DS, the more cation anchor sites it has, and the more effective it is as a protective colloid (Lubbers et al., 1993).
In the past, CMCs were poorly defined compounds, with relatively heterogeneous DPs. Their viscosity was unreliable, to the point that they could modify the viscosity of a wine. The CMCs currently on the market have much more clearly defined characteristics, and quality control is more effective, resulting in purer products. Minimum purity is 99.5%, with a sodium content between 7 and 8.9%. Viscosity varies from 25,000 to 50,000 mPa at 25°C, depending on the type of CMC selected. These low values cannot therefore alter the viscosity of the finished beverage.
The production and use of CMCs as a gelatin substitute dates back to the 1940s and 1950s. They are now used in the food and beverage industry (code: E466), at levels up to 10 g/l or 10 g/kg, as well as in cosmetics and pharmaceuticals. The CMC content of alcoholic and nonalcoholic beverages may be as high as 500 mg/l.
Water solubility of CMCs is variable, depending on their degree of substitution and polymerization. They owe their hydrophilic qualities to their highly hydroxylated carbohydrate character. CMCs used in very sweet beverages are less viscous, probably due to the formation of hydrogen bonds between the sugar and the gum. CMC–sucrose interactions depend on the order in which the products are added: if the sugar is dissolved in the water first, its hydrophilic character reduces the solubility of CMC (Federson and Thorp, 1993). This should be taken into account when preparing the concentrated CMC solutions (20–40 g/l) used to treat beverages, such as wine, that require a restricted addition of water (0.05–0.1 l/l).
FIGURE 1.23 Structure of a carboxymethylcellulose (CMC) chain.
FIGURE 1.24 Formula for the etherification of celluloses (R–[OH]3) by sodium chloroacetate.
CMCs are also reputed to promote solubilization of proteins and stabilize solutions containing them (Federson and Thorp, 1993). This property is useful in winemaking for the purpose of preventing protein haze. These CMC–protein interactions may be compared with the carbohydrate–protein association in glycoproteins, such as yeast mannoproteins.
TABLE 1.23 Treating Various Wines with CMC (Results After One Month at −4°C; See Figure 1.25)
| Wine treated | Dose of CMC used (g/hl) | Comments |
|---|---|---|
| Red A.O.C. Bordeaux | 2 | Unfiltered |
| Red A.O.C. Buzet | 4 | Filtered prior to treatment |
| White A.O.C. Bordeaux | 4 | Fined, treated with CMC, then filtered |
| White vin de pays (Gers) | 4 | Fined, treated with CMC, then filtered |
| White vin de pays (Loire) | 4 | Fined, treated with CMC, then filtered |
| Sparkling wine (Gers) | 4 | Treated prior to second fermentation |
CMCs are available in the form of powder or white granules. As these absorb humidity from the air, they must be stored in a dry place. Their use in winemaking has been authorized in the EU. Recent results (Crachereau et al., 2001) indicate that low‐viscosity CMCs are effective in preventing tartrate crystallization at doses 12–250 times lower than those currently used in the food industry. A dose of 2 g/hl is often ineffective, but it should not exceed 4 g/hl in wines supersaturated with potassium bitartrate. Details of the results are given in Table 1.23 and Figure 1.25.
These results demonstrate comparable effectiveness for metatartaric acid (10 g/hl) and CMC (4 g/hl). Furthermore, a comparison of the stability and effectiveness of these two additives, following prolonged heat treatment at 55–60°C for 5–30 days and one month at −4°C, showed that CMC was perfectly heat stable. It was still perfectly effective, whereas metatartaric acid became totally ineffective after only five days at 55–60°C (Peynaud and Guimberteau, 1961; Ribéreau‐Gayon et al., 1977).
FIGURE 1.25 Comparison of the effectiveness of metatartaric acid and carboxymethylcellulose on turbidity due to tartrate crystals (Crachereau et al., 2001) (see Table 1.23 for treatment conditions).
The effectiveness of CMC is due to its property of significantly reducing the growth rate of crystals: a dose of 2 mg/l reduces crystal growth by a factor of seven (Gerbaud, 1996). CMC also modifies the morphology of potassium bitartrate crystals.
In the case of wines intended for a second fermentation, three different CMCs produced a more stable, persistent bead. Only the CMC with the highest molecular weight caused a slight increase in bubble size. A similar inhibition of crystallization has also been observed in Champagne base wines (A. Maujean, personal communication).
All these positive results, combined with the fact that these CMCs are easy to use, relatively inexpensive, and do not require special investments, led to their authorization for use in winemaking by the OIV in June 2008 within the limit of 10 g/hl or 100 mg/l. Its transposition into European law via EU regulation 606/2009 also authorizes its use in red and rosé wines at the same maximum dose (10 g/hl or 100 mg/l). Tartrate stability in red wines is more difficult to obtain than in white and rosé wines. The effectiveness of the treatment is proportional to the dose of inhibitor used. For wines with medium to high instability, the use of CMC (at 10 g/hl) improves tartrate stability. However, it does not always help obtain total stability after the cold test. Only slightly unstable red wines are stabilized by CMC.
The effectiveness of CMC in tannic red wines, with the most complex colloidal structure, can lead in some cases to a destabilization of the coloring matter. This