Carboxymethylcellulose (CMC) is a crystallisation inhibitor used to infer cold stability on wines and was approved for winemaking in Australia in 2011. Since then, the AWRI has received queries regarding CMC and its use in relation to tartrate stabilisation. The main queries associated with CMC use are discussed below.
CMC is a cellulose derivative which is synthesised by the reaction of cellulose with chloroacetic acid in basic solution. As such, CMC cannot be considered to be a natural product. However, CMC is safe to use in food production as it is not degraded or reabsorbed in humans.
CMC dissolves readily in water or wine, but should be left to swell overnight. Dry/granular forms of CMC might be difficult to prepare in some wineries, as very vigorous stirring can be required to dissolve the CMC due to high viscosity. It is suggested that liquid forms of CMC are easier to handle in large quantities. Liquid CMC can be diluted with wine to the required volume of the product, which can then be added to the wine tank with homogenisation.
CMC has the ability to crosslink with proteins in wine to form a haze. Consequently, wines must be protein stable before any CMC additions. In fact, a wine must be ‘bottle ready’ before making a CMC addition and no subsequent physicochemical modifications can be made after the addition. That is, all blending, acid adjustments or deacidification treatment, concentrate additions etc. must be made and the wine must be free of any particulate matter before CMC treatment. Note that lysozyme is a protein and can generate a haze if present with CMC.
Manufacturers of CMC generally do not recommend any filtering operations at all within a minimum of 24 to 48 hours after the CMC addition. CMC needs to be fully solvated before attempting to filter, otherwise filters might block and CMC might be removed from solution. Consequently, it is recommended that two to five days be allowed for the CMC to integrate fully with the wine before any filtration.
Different CMCs vary in their degree of polymerisation and the degree of substitution. Therefore, different CMCs will vary in their effectiveness. Consequently, the rate used should be that specified by the manufacturer. In general, the rate specified by the manufacturer is sufficient to achieve stability but the actual required effective dose can be wine variety dependent. In the case of wines with a high tartrate loading, or in the case of rosé wines, a trial should be conducted in order to determine the rate required.
The AWRI recommends that cold stability be determined by storing a filtered 150 mL aliquot of wine at –4°C for three days, and then examining it for the presence of a crystalline deposit. This test (commonly called the cold or brine test) is recommended based on the results of a study conducted at the AWRI of various cold stability methods. This study showed that the 3-day/–4°C test related well to the actual deposition of crystals in wine over time. Some people use a freeze thaw test. Whilst such a test may be used as a rough and quick overnight guide of gross instability, the freeze thaw test is the least preferred method for testing cold stability due to its propensity to give false positive or false negative results.
Another method, which can be used in conjunction with the brine test, is the so-called saturation temperature (Tsat) test. The brine test gives information on the current stability of the wine, whereas the saturation temperature test gives an indication of potential stability (i.e. the wine’s potential to become unstable over time). Consideration of the results of both of these tests together gives the clearest indication of a wine’s status and helps develop the best strategy for long-term stability. For example, if a wine fails both the brine and Tsat tests, then the wine is both currently unstable and potentially unstable. In this case, it would be best to start with traditional cold stabilisation first. If a wine passes the brine test but fails the Tsat test, then the wine is currently stable but could potentially become unstable in the future. Such a wine is a good candidate for CMC. If a wine passes both the brine and Tsat tests, then the wine is both currently and potentially stable. No action is required in this case, as the wine is very unlikely to throw a tartrate deposit.
Suppliers of CMC do not generally recommend its use for wines with potential calcium tartrate instabilities. Due to the different surface charge of calcium tartrate crystals compared to potassium bitartrate crystals, the effectiveness of the interaction with CMC is altered. Therefore, winemakers should not rely on CMC to stabilise a wine with respect to calcium tartrate instability.
CMC is not recommended for red wines as it has been found to be inefficient as a crystallisation inhibitor in red wine and has been found to cause the precipitation of colour. CMC might be effective in some rosé wines, however, bench trials should be conducted to assess potential colour precipitation and effectiveness prior to use.
The most viscous CMCs have an effect on mouth-feel, but this is not necessarily undesirable. The sensory impact is minimal or nil if the CMC is of high quality. In one study, one winemaker tasted the trial wines and did not detect any differences between the control and CMC-treated wines. The sensory impacts of CMC are difficult to predict and it is recommended that CMCs be trialled before use. It is also suggested to allow two to seven days for the CMC to integrate fully into the wine before assessing for flavour impacts.
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