Alternative additives to sulphur dioxide in winemaking

6 and 9.7) are naturally occurring, legal alternative additives to SOj, however, they have also recently come under scrutiny. 

The antimicrobial activity of these compounds is pH-dependent, as all are inhibitory to yeast growth when in an undissociated form. To interfere with microbial metabolism, it is necessary for the sorbate or benzoate to pass through the cell membrane. The cell membranes of yeasts and moulds are ionically charged and do not permit the transfer of negatively charged molecules. At neutral or near neutral pH, sorbic and benzoic acid molecules are almost completely ionised and cannot be transported across the cell membrane they are effectively inactive. As the pH decreases, the concentration of the unionised form increases and hence the antimicrobial activity of the acids increases (Schmidt, 1987). 

Sorbic acid (an unsaturated fatty acid) is permitted in wines at a concentration up to 300 mg/1 according to the country (200 mg/1 in the EC and Australia, and 300 mg/1 in the USA), but it is generally added at the lower concentration of 100-200 mg/1 (Kunkee and Goswell, 1977 Splittstoesser, 1982 De Rosa et al., 1982). It is generally added as potassium sorbate. Like SO2, sorbic acid is most active in the unionised form or at lower wine pH values (Amerine and Ough, 1980). Indeed, an advantage of sorbic acid is that the undissociated form is present in the greatest concentration (93-98%) at the normal wine pH of 3.0-3.8 (Sofos and Busta, 1981, 1983). Above pH 3.8, a dose of 200 mg/1 may be inadequate. Benzoic acid. 

While currently not a permitted additive in wine in Australia, Canada or the EC (although it may be added to soft drinks), an alternative to DEDC is the analogue dimethyldicarbonate (DMDC), which is observed to have antimicrobial properties similar to DEDC (Genth, 1979, 1980) without the production of ethyl carbamate (Ough, 1983). Dimethyldicar- 

These compounds are generally added to wine post-fermentation/pre-bottling either as a substitute for SO2 or an adjunct to SO2, thereby reducing the concentration of SO2 necessarily added to the wine however, DEDC and DMDC have no antioxidant role. 

---