Sorbic Acid

Brief Description :

Sorbic acid is a short-chained unsaturated (has double bonds) fatty acid. Its iupac name is 2,4 hexadienoic acid and its chemical formula is C6H8O2. It has a carboxylic tail which has a pKa of 4.76. Its melting and boiling points are 136 and 228 degrees Celsius, respectively. It is commonly used by the food industry as a preservative because its mineral salts have antimicrobial properties in acidic solutions. Its undissociated form is several degrees more antimicrobial then its dissociated form and is a function of pH, yet both have antimicrobial properties. It is particularly effective against fungi and has the advantage of not diminishing overtime. Generally, a fungistatic dose in the presence of ethanol and sulfur is roughly 200 mg/L. It can also be used to remove mineral deposits. Sorbic acid by itself has subtle sensory characteristics, but a portion of the population finds it particularly offensive.

Application in Wine Microbiology:

Sorbic acid is often applied prevent off-dry wines from fermenting in the bottle. It is generally used to inhibit Saccharomyces, which it is fairly good at doing. An issue with this is that lactic acid bacteria, specifically Oenococcus can esterify it into an alcohol (sorbyl alcohol) and then it has the tendency to rearrange and become 2ethoxyhexa-3,5-diene, which has a potent, geranium-like odor that is unpleasant. Its sensory threshold has been reported to be around 100ng/L, which is a relatively small amount. Other geneses within lactic acid bacteria have not been reported to be able to metabolize Sorbic acid. To minimize the potential for this off odor in sweet reserves and when blended back, wines should have the solids removed, be filtered, properly sulfited and kept at low temperature.

References:

  • Boulton, R.B., V.L. Singleton, L.F. Bisson, and R.E. Kunkee. 1999. Principles and Practices of Winemaking. Chapman & Hall, New York.
  • Fugelsang, K.C. and Edwards, C.G. 2007. Wine Microbiology: Practical Applications and Procedures.  Springer Science+ Business Media, New York.
  • Eklund, Trygve. 1983. The antimicrobial effect of dissociated and undissociated sorbic acid at different pH levels.  Norwegian Food Research Institute. Journal of Applied Bacteriology. 54: 383-389.