Quite the catchy title! But it’s true.

Whether motivated by health concerns or wine chemistry effects, the wine industry has long been looking for alternatives to the use of sulfites to protect wine against oxidative effects and microbial spoilage.

There have been some solutions, such as ascorbic acid and lysozyme, which have proven effective to some degree on protecting against oxidation or microbial spoilage, but usually not both. And most have limited or transient efficacy, or are contraindicated for certain wines; for example, ascorbic acid is not recommended in reds as its degradation products react with polyphenols and alter color, and lysozyme is most effective against lactic acid bacteria only and at high pH but which also has reduced efficacy in reds because of polyphenols.

And so the use of sulfites persists.

The problem with sulfites, particularly in reds, is that they react with other compounds and become sequestered and no longer afford any protection. It is said that free sulfur dioxide (FSO2)—which is what protects wine—becomes bound (BSO2). Although total SO2 (TSO2) remains constant, assuming no loss of FSO2 to the environment, the amount of FSO2 has decreased and much less of it is now available to protect wine. So we have to add more sulfite to increase FSO2, and the chemical reaction cycle continues.

Binding reaction between a carbonyl and a bisulfite ion in wine

One of the principal compounds that sequester FSO2 is acetaldehyde; more generally, it is the class of compounds known as carbonyls, which include pyruvate. Acetaldehyde and pyruvate (pyruvic acid) are by-products of yeast fermentation; acetaldehyde also results from ethanol oxidation while pyruvate also results from bacterial metabolism.

These carbonyl compounds have a great affinity for SO2, and more specifically its bisulfite (HSO3‾) form at wine pH. So carbonyls and bisulfite ions bind and thus reduce SO2 efficacy.

The solution would be to “remove” carbonyl compounds so that bisulfite ions do not become bound and SO2 continues to protect wine. Since there is no known method of physically removing acetaldehyde molecules, at least no without impacting wine quality, is to look for another binding agent, one which has no affinity for bisulfite ions and which does not impact wine quality.

Binding reaction between phenylsulfonylhydrazine and a carbonyl
(Adapted from Blasi et al., 2008)

Well, this has now become reality and the patented process will soon find its way into commercial winemaking once the process introduction details have been sorted out and the additives approved by the various health, wine and food control agencies.

The method uses phenylsulfonylhydrazine grafted on an insoluble support, such as lignin. Phenylsulfonylhydrazine binds with carbonyls (using a direct mechanism than bisulfite ions), and then the phenylsulfonylhydrazine–carbonyl–support complex falls as a precipitate, which can be removed by racking. Research has demonstrated that as much as 80% of acetaldehyde can be removed with this method.

Reference

Blasi, M., J-C. Barbe, D. Dubourdieu, H. Deleuze. (2008). “A New Method for Reducing the Binding Power of Sweet White Wines”. The Journal of Agricultural and Food Chemistry, 56; 8470-8474.