Sorbic acid: Difference between revisions

Sorbic acid is a short-chain fatty acid which, together with its salt, potassium sorbate, exhibits antimicrobial properties.<ref>Zoecklein BW. [https://www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Wine%20Microbiology/Micro2.pdf Controlling microbial growth in wine.] Wine/Enology Grape Chemistry Group at Va Tech.</ref> Owing to its solubility, potassium sorbate is often used instead of sorbic acid. It is added as a yeast inhibitor in sweet wines (greater than 2.0 g/L reducing sugar). This compound does not kill yeasts but, if properly employed, inhibits their growth. Sorbate has little practical inhibitory effect on the growth of acetic acid bacteria, lactic acid bacteria, or oxidative (film forming) yeast and the spoilage yeast Dekkera. The effectiveness of sorbic acid (potassium sorbate) in controlling fermentative yeast in wine is dependent upon the following: wine pH, free [[sulfite|sulfur dioxide]] content, percent alcohol by volume, sorbic acid concentration. The lower the pH of the wine, the greater is the percentage of sorbic acid that is undissociated. It is the undissociated acid which controls yeast inhibition. An increase in pH (the result of a malolactic fermentation, for example) decreases the percentage of the undissociated compound and, therefore, reduces the effectiveness of yeast inhibition. Potassium sorbate should only be added to sweet wines, just prior to bottling. Oxidation of wines containing potassium sorbate results in a flat, butter-like off odor. Wines bottled with this compound should contain sulfur dioxide to avoid oxidation. The growth of lactic acid bacteria in the presence of sorbic acid produces a potent odorous compound (2-ethoxyhexa-3,5-diene) that is responsible for the so-called "geranium tone." High free sulfur dioxide levels (approximately 30 mg/L, depending upon the pH) must be achieved at bottling to prevent lactic acid bacterial growth in the presence of sorbic acid, and to aid in limiting wine oxidation. Potassium sorbate is generally employed at levels of 150-300 mg/L sorbic acid. Sweet wines low in alcohol and free sulfur dioxide, and wines high in pH, require more of this compound for stabilization. The average detectable threshold is 135 mg/L sorbic acid, with the minimum detection level approximately 50 mg/L. It should be noted that the threshold is much lower for wines that have undergone oxidation in the presence of sorbic acid and to aid in limiting wine oxidation. The use of sorbate in wines designed for long-term aging is contraindicated. As stated, owing to its solubility, potassium sorbate is often used instead of sorbic acid. To determine the amount of potassium sorbate to employ to obtain a given level of sorbic acid, the following relationship can be used: Weight of potassium sorbate required = 1.34 x addition level of sorbic acid (mg/L)