Making A Caseby Keith Stewart
Is drinking wine sold with screwcaps compromising your health?
The screwtop debate that has fizzed on among wine enthusiasts and professionals over the past few years has been lost on most wine drinkers. They just want their wine to taste good and be relatively easy to get at. But what if wine under screwcaps compromised your health, lowered sperm counts and was a factor in increasing breast cancer statistics?
Winemakers have adopted screwcaps, and other technological replacements for natural cork, because of the nasty taste of TCA. This chemical compound - 2,4,6-trichloroanisole - is one of the results of an environment polluted with synthesised chemicals. TCA is created by soil organisms reacting against poisonous chlorine-containing pesticides and it's readily absorbed by cellulose (cork, in other words), resulting in wine that smells of old socks and tastes of cabbage juice.
Naturally, winemakers confronted with the return of numerous cases of "cork-tainted" wine began looking for alternatives. Most New Zealand wine producers concluded that the taint problem would be eliminated efficiently, and cheaply, by adopting aluminium screwcaps sealed with a plasticised liner. But this, in turn, is implicated in the rising concern over endocrine disruption.
Dr Neil McCallum, whose Dry River winery continues to use natural cork sealed with a dob of wax, is suspicious of wine exposure to the plastic film in screwcaps, and as a chemist is surprised, given the risk to human health, that no industry research has been done.
"Alcohol is pervasive in all parts of the body and as alcohol is well known for increasing or modifying chemical activity, we should always proceed with caution," he says.
McCallum says there is no evidence that a change from cork is in the interests of wine quality and he is concerned that the Screwcap Initiative did not investigate the health implications of adopting new closures.
The Screwcap Initiative is a group of winemakers, mostly from New Zealand and Australia, who have aggressively promoted a change to screwcaps in response to TCA problems. One of its leaders, John Belsham of Foxes Island, is blunt when asked about the concerns over endocrine disruption.
"We didn't consider it, because we were unaware there was an issue. Still are," he says. His stance is echoed by all six screwcap-using winemakers approached by the Listener, who confessed they had no concerns about the possible health effects of plastic film in screwcaps because they hadn't heard anything about endocrine disruption.
In response to enquiries, New Zealand screwcap distributors and producers say that the plastics used are "food grade". As New Zealand Winegrowers' Dr John Barker says, "The question [of endocrine disruption] has never been raised as a food safety issue for wine at Food Standards Australia New Zealand, or by the OIV [the international wine industry organisation]. I have certainly never come across it."
The troubling aspect here is the thin film of PVDC that is the active seal inside the screwcap that protects the wine from oxygen. PVDC, or polyvinylidene chloride, is one of the endocrine disrupters identified in the growing body of research linking these to humans. The cling film Saran Wrap contained PVDC from the 1950s until 2004, when S C Johnson changed the formula out of "environmental concerns", replacing it with low-density polyethylene (LDPE), which contains no toxic chemicals. Glad Wrap is also LDPE-based.
The wine industry is aware that PVDC is the prime material in the screwcap system. In the Screwcap Initiative's opening media presentation in June 2002, the point was made that the seal was a ".80 micron layer of neutral PVDC film, which is in contact with the wine, and the bottle rim".
Other solutions to the TCA problem could also hold dangers. Some winemakers have adopted corks made of reconstituted, purified cork dust, in what is commercially known as the DIAM process. The producers of DIAM corks refuse to specify what the bonding agent is that keeps their cork-shaped dust cylinders together, and whether it involves bisphenol A, the disruptive component in PVDC.
Best food industry practice is to consider the possible influences on human health before changing packaging. Certainly, the wine industry is well aware of the risks of urethane - a byproduct of fermentation that has been a food safety issue for wine, beer, spirits and food items like cheese - for as long as it has existed.
New Zealand producers have well-established research on urethane production, on how to identify it and to reduce or avoid it, so are unlikely to be concerned about the addition of urethane (ethyl carbamate) to the World Health Organisation's list of carcinogens. They are well aware of their responsibility in matters of public health.
With around 80 percent of New Zealand wine now under screwcaps, the concerns over PVDC need to be addressed - for the health of the industry as well as that of consumers.
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