Potassium Sorbate (Sorbic Acid)
Potassium sorbate, a widely used food preservative, is added in small quantities to sweet or semi-sweet wines to prevent further sugar fermentation. It is the only practical way for the home winemaker to guarantee that fermentation will not restart in the bottle. Sorbate is never used with completely dry wines. And it should not be used where there is a possibility of malolactic bacteria being active in the bottle.
How it works
When dissolved in water, potassium sorbate (CH3CH=CHCH=CHCOOK) breaks into sorbic acid and ionic potassium. It is sorbic acid that has selective anti-fungal, anti-microbial properties. It inhibits yeast very effectively—it does not kill yeast cells, it only prevents their growth and activity. Therefore, before sorbate is added, a wine should be racked clear in order to reduce the number of yeast cells.
Sorbic acid itself is soluble in alcohol but virtually insoluble in water. However, potassium sorbate, a salt of sorbic acid, is very soluble in water and virtually insoluble in alcohol. This is why sorbate is used to carry the sorbic acid into the wine.
- Sorbic acid is very stable in wine. It does not combine with other elements and thereby lose its potency. So there is no point in adding any more than necessary.
- Sorbic acid is not effective against many bacteria. It MUST be used in conjunction with SO2 to control acetic acid and malolactic bacteria. The major danger in adding sorbate to wine is active malolactic bacteria. They can metabolize sorbic acid and produce a disastrous bi-product called hexanedienol that has a strong geranium-like smell. This will ruin the wine, and there is no way to recover from this fault. Therefore, make sure ML bacteria are under control (via Lyzozyme, pH, and SO2) before you add sorbate.
- Sorbate, like SO2, is more effective at lower pH. Therefore wines like Riesling, which tend to have a lower pH, will not need as much sorbate as social wines that have been made from other varieties of ripe grapes.
- Less sorbate is needed with high alcohol wines, because alcohol itself inhibits yeast activity.
- The amount of sugar in the wine has no effect on the amount of sorbate needed. The only concern (besides pH and alcohol) is the initial population of yeast cells, which should be below 100 per milliliter. Home winemakers usually have no means to assess this, so they simply rack a wine as clear as possible before adding sorbate.
How much to add
Additions to wine are always specified in grams or milligrams of sorbic acid per liter. Because potassium sorbate is about 75% sorbic acid by weight, it is very easy to make the conversion — just increased the desired weight of sorbic acid by one-third to get the required weight of sorbate.
EU regulations limit sorbic acid additions to wine to 200 mg/L (0.2 g/L). The BATF (American) limit is 300 mg/L. Normally, home winemakers will require less, depending on the alcohol and pH of their wines.
The available recommendations on sorbic acid additions are not entirely clear. In a recent review, Gallander (1999) cites a 1960 study that suggests 80 mg/L is enough. The most widely quoted recommendations come from Peynaud (1984: 275), who is specific about alcohol levels but vague about pH. He says that that sorbic acid is twice as effective at a pH of 3.1 as it is at 3.5 and that wines above 3.5 in pH may require sorbic levels in excess of the 200 mg allowed by the EU. Unfortunately, when he makes his recommendations for different alcohol levels, he does not say what pH he is assuming (see the table below):
|Note: these recommendations presume a pH < 3.5, good clarification, and adequate SO2.|
NOTE: If you don't have an accurate scale, 1 tsp of potassium sorbate weights about 2.9 grams.
Sorbic acid has been used as a food preservative for the past 50 years and it has GRAS (Generally Regarded As Safe) status. It is a polyunsaturated fatty acid, which the body metabolizes like it metabolizes other fatty acids. Even in relatively large amounts, it is not considered a health hazard. It is commonly used in the preservation of bakery goods and chesses at many times the level it is used in wine.
However, organic authorities consider sorbate and sorbic acid “synthetic” (potassium sorbate is manufactured) and do not permit it as a seed coating or a food preservative. Sorbate and sorbic acid are also skin and eye irritants and should be handled with care. (See the OMRI study listed in sources.)
Avoiding the use of sorbate
Larger commercial wineries today can avoid sorbate in sweet wines by sterile filtering, but this is not an option for the home winemaker. Those who want to avoid sorbate can take some comfort from the fact that sorbic acid is a relatively recent (since WW II) wine additive. For many years winemakers successfully produced sweet wines without it, and some still do. No one says you can't make sweet wine without sorbate, they only say it is riskier. To reduce this risk you can:
- Use a yeast with low alcohol tolerance.
- Make sure there is no yeast activity in any sweet reserve you add.
- Rack the wine very carefully and filter with as fine a filter as you can.
- Store the wine in very cool conditions.
- Pray—and drink the rest of the wine up fast if you begin to notice a spritz.
Gallander, Jim (1999). "Sorbic Acid as a Preservative in Wines II: Application Levels." Vineyard Vantage, May 1999. This publication is available on the Ohio State University website at http://www.oarde.ohio-state.edu/grapeweb/vinvan/vinvan0599.htm
Organic Materials Review Institute (2002). National Organic Standards Board Technical Advisory Panel Review, Potassium Sorbate . http://www.omri.org/Ksorbate_final.pdf
Peynaud, Emile (1984). Knowing and Making Wine, second French edition, trans. by Alan Spenser. John Wiley and Sons.
See also: Bill Collings, "Potassium Sorbate" on the BCAWA website, which I noticed after partly rediscovering the wheel with this article. http://www.bcawa.ca/winemaking/sorbate.htm
Drafted by Rod Church, January 15, 2004.