After conducting extensive tests, the team determined that the molecular form of sulphur dioxide (SO2) is the culprit.
Winemakers regularly use it as an antioxidant and antimicrobial, and it does not cause any issues when wine is stored in glass bottles.
However, SO2 interacts with the aluminium cans in different ways, and it can lead to the dreaded rotten egg smell.
Producers tend to use an ultra-thin coating inside the can to keep the wine and the aluminium apart, but it is often not enough to stop the interaction.
It does not occur immediately, but the longer the can sits on the shelf, the more likely the bad smell is to arise.
Professor of food Gavin Sacks, who led the research along with Julie Goddard, said: ‘Of all the things we measured, most had no correlation. The one that stood out was molecular SO2.
‘With that, wineries typically aim for about 0.5 to one parts per million (ppm). We were noticing that in wines with more than 0.5 ppm molecular SO2, we had sizeable increases in hydrogen sulphide, the rotten egg smell, within four to eight months.’
The researchers found that maintaining 0.4 ppm of SO2 in wine and using epoxy liners could allow cans to have a shelf life of up to eight months, without the foul odour arising.
‘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 great for preventing oxidation.’
One solution would be to use thicker liners, but they are more expensive to produce, and they are less environmentally friendly, as the thicker plastic is burned off during the aluminium recycling process.
Sacks and Goddard revealed that there is an irony to molecular SO2 being the smelly culprit for canned wine.
Levels are typically lower in red wines than in white wines. However, consumers tend to associate cans with cheaper wines, so many producers do not package their red wines in cans
‘If you go to a store, you’re far more likely to see sparkling, white and rosé wine in cans, but unfortunately those are the products that are more likely to have issues,’ Sacks said.
Sacks and Goddard have teamed up with Héctor Abruña, professor of chemistry, to design more robust liners using food-grade materials that can prevent corrosion. The group has secured funding from the US Department of Agriculture’s National Institute of Food and Agriculture for this project.
