WINE, any connoiseur will tell you, is a living thing. And as with other organisms, for it, too, oxygen is a mixed blessing. The element breathes life, but it—or strictly speaking reactive oxygen species (ROS), the byproducts of the process through which cells extract energy from nutrients—can be toxic. Oxygen plays a role in red wines’ normal ageing process. However, through ROS, it can lay waste whites. It can be kept out using screw-top bottles instead of less airtight corks, but many aficionados frown on such departures from tradition; France bans screw-tops outright.
As the oxygen molecules permeate the cork, they react with trace amounts of positively charged iron ions (atoms that have lost some of their electrons) that occur naturally in wine. The encounter sets off a cascade of reactions that produces ROS, which destroy desirable aromatic compounds. The upshot is a flat, brownish liquid with an overpowering whiff of apple (from acetaldehyde, one of the reactions’ products).
One way to prevent this from happening (other than resorting to screw-tops) is to rid the wine of iron. The trouble is, the “ion exchange” techniques typically used to extract trace metals also tend to flush out the aromatic compounds. An alternative approach, as Ryan Elias, of Pennsylvania State University, and his colleagues report in the Journal of Agricultural and Food Chemistry, is to lace the booze with a chelating agent.
Chelating agents are molecules that mop up metal ions and thus restrict their ability to partake in chemical reactions. Because wine contains thousands of compounds, Dr Elias and his team simplified their experiments by using a “model wine” made of ethanol (to give the solution 12% alcohol content), tartaric acid (found in grapes), as well as some aromatic compounds responsible for a wine’s bouquet and flavour. And, of course, some iron ions. They then added different types of iron-binding chelating agents and infused the resulting tincture with copious amounts of oxygen, and analysed its chemical composition.
They found that the chelating agents, including taste- and odourless ones like EDTA, a common food preservative, blocked the formation of 1-hydroxyethyl, an nasty ROS. At the same time, the quantity of malus acetaldehyde dropped whereas that of 3-mercaptohexan-1-ol, responsible for soupçons of tropical fruit, was preserved.
There are niggles. For one thing, some of the most effective chelating agents Dr Elias tried are themselves toxic, and so unsuitable for human consumption. Dr Elias’s model wine was also much less complex than regular wine; the chelating agents may not, he confesses, work as well in less controlled conditions. Strict rules about what can be added to wine mean that pouring in even a non-toxic chelating agent such as EDTA would require regulatory approval. Finally, it is unclear whether the snootiest winedrinkers would embrace such chemical experiments. They might as well settle for screw-tops.