Extensive testing led the research team to identify the material known as sulphur dioxide (SO2) as the main offender.
It’s commonly employed by winemakers as an antioxidant and antimicrobial and doesn’t present any problems when the wine is kept in glass bottles.
But, when in contact with aluminium cans, the behaviour of SO2 changes, potentially resulting in the unwanted scent of rotten eggs.
To try to mitigate this interaction, producers often apply an extremely thin layer within the can intending to separate the wine from the aluminium, however, this is frequently insufficient.
The development of an unpleasant odor is not immediate, but the chances of it happening increases the longer the can remains unused.
According to the research spearheaded by food Professor Gavin Sacks and Julie Goddard, there’s mostly no correlation among the things they measured. However, molecular SO2 was a notable exception.
Sacks stated, ‘Wineries usually target about 0.5 to one parts per million (ppm) of molecular SO2. In our observation, wines containing over 0.5 ppm molecular SO2 had significant increases in hydrogen sulfide, known for its infamous rotten egg smell, within a span of four to eight months.’
Findings revealed that keeping 0.4 ppm of SO2 in wine and the use of epoxy liners, can extend a can’s shelf life to eight months, and prevent the emergence of the unpleasant smell.
‘We’re suggesting that wineries aim on the lower end of what they’re usually comfortable with,’ said Sacks. ‘Yes, there’s going to be the chance of having more issues of oxidation. But the good news is that cans provide a hermetic seal. They’re not likely to let in any air if the canning is done properly, which is why brewers love them. It’s excellent for preventing oxidation.’
One answer could be to use liners of more substantial thickness, but they cost more to produce, additionally, they aren’t as eco-friendly, since during aluminium recycling process more plastic gets burned off.
Sacks and Goddard stated that molecular SO2 being the stinky offender for canned wine bears some irony to it.
Typically, it is lower in red wines as compared to white wines. However, as consumers often link cans to cheaper wines, many producers avoid packaging their more exquisite red wines in cans
‘If you visit a store, you’re much more inclined to see cans of sparking, white and rosé wine, but sadly these are the types of products more susceptible to problems,’ said Sacks.
Sacks has collaborated with Goddard and Héctor Abruña, a professor of chemistry, to engineer superior liners using food-grade materials to counteract corrosion. The team has received financial support from the US Department of Agriculture’s National Institute of Food and Agriculture for the project.