South African wine exports bring in more than $650m per year from a little less than half of total local production of around 450 million litres per year.
An important and often maligned constituent of this wine is sulphur dioxide (SO2), which exists in very small quantities in all wines, even those labelled ‘no sulphur added’, which typically contain up to 10 mg/ℓ or 10 ppm (parts per million).
It was first used in winemaking by the Romans, who discovered burning sulphur candles inside empty wine vessels kept the wine free of the ‘vinegar smell’ for much longer.
A German royal decree of 1487 was the first recorded ‘permitted’ use of SO2 in winemaking and, like the Romans, it was used to disinfect the barrels used for storing the wine. SO2’s use as a disinfectant is still common today, because bleach-based products cannot be used in a winery due the risk of cork taint.
Afrox SO2 is widely used to sterilise wine and beer making equipment in order to inhibit the growth of moulds and bacteria, while controlling wine fermentation. It can also be used in a variety of disinfecting and fumigation applications.
Afrox’s Production Quality Manager, Hans Strydom, talked to gasworld about the vital role SO2 plays in enabling South African wines to be exported and enjoyed by people from every country in the world.
“SO2 in wine inhibits the growth of microorganisms such as yeast and bacteria and slows down the oxidation process, which alters the wine’s colour and odour making the wine darker and dryer,” he explained.
“Too much oxidation will ruin a wine, but controlled oxidation adds character and complexity and is, in some cases, an integral part of production and aging processes.”
“South African legislation limits the allowable amount of SO2 depending on the wine style: 150 mg/ℓ for dry red wines; 160 mg/ℓ for dry whites; while off-dry and sweeter wines may contain up to 200 mg/ℓ and late harvests, up to 300 mg/ℓ.”
Afrox SO2 and winemaking
While SO2 can be added to wine in the form of potassium metabisulphite, Afrox gases are more usually fed directly into the wine via carefully monitored dosing equipment.
“At Afrox we can meet all of the requirements of winemakers: delivery; handling and safe management of SO2. Through our local network, we can also help to optimise production processes, satisfy regulatory compliance and deliver on the environmental agenda,” said Strydom.
“And while organic wines are becoming more popular due to the additive free winemaking processes used, they do still contain SO2 and sulphites – albeit at very low levels.”
The shelf life of these wines is significantly limited, however, which makes them a much less attractive option for export.
“The systematic and controlled use of this Afrox gas as an additive – mostly during bottling but also during earlier stages for some of the sweeter styles – controls fermentation and stabilises the bottled wine,” Strydom said.
“The desirable pure yeast cultures used to make good wine are highly resistant to SO2’s antifungal effects, while the undesirable yeast strains are not. The net result is that the use of Afrox SO2 will produce a better quality wine.”
“Without SO2, most wines would have a shelf life of three months or less and, without exceptional effort, their quality would be inferior,” he concluded.