The vast majority of wine bottles have small print on the reverse label stating “Contains sulfites.” I’m always curious when food or beverages have such a label – is this some sort of warning or something I should be concerned about? A bit like ‘contains phenylalanine’ on diet drinks. So, some background for you…
Sulfur is used in wine making as a preservative – it helps stop bacteria and oxidation, which if not stopped will soon transform a beautiful wine into sour vinegar. Interestingly grape juice has some naturally occuring sulfur which is a byproduct of fermentation (small amounts can be found in bread too). However more needs to be added to bind to oxygen and stop the vino breaking down into vinegar. It is also helpful that bacteria also don’t grow well around sulfur. Bacterial growth could be stopped by pasteurising but adding just a tiny amount of sulfur is easier and more effective.
Sulfur is added at the first stage of wine making – to kill any bacteria and moulds that may be on fruit – and again at the end stage to get rid of any oxygen, when the wine is made but needs preserving. It is not usually added during fermentation as the little yeasties wouldn’t be happy!
Wikipedia reports that the acceptable daily intake is up to 0.7 mg per kg of body weight (far more than what the average bottle of wine contains) and that sulfites (sodium metabisulfite) have no side effects; and are oxidised in the liver to harmless sulfate and excreted in the urine.
So if sulfites have been added to food and beverages to effectively and safely preserve them for hundreds of years, why should anyone be concerned?
Well, even though the amounts in wine are miniscule, apparently sulfur may cause problems for sensitive asthmatics – aggravating the mucous membranes of the respiratory system. Some folk are also allergic to sulfur. I know I come out in a rash if I take sulfur based medicinal drugs, although I’ve never reacted to wine in that way – I assume because the sulfur levels are so low. Sulfur ‘allergies’ however don’t usually cause a life threatening auto-immune response but rather the symptoms are more commonly rashes or a headache (not to be confused with the over indulgence wine headache ;-) ). And so it appears that ‘Contains sulfites’ sounds like a warning, but for the vast majority of us there is little to be afraid of. In saying that, it is only fair that consumers are informed and that if they would like to try a sulfur free wine they should be able to. Then they can see for themselves if it makes a difference.
With this in mind, we are trialling a sulfur free Sav Blanc this year. I asked Aaron how he will deal to unwanted bacteria and oxygen without the sulfur weapon and he explained that there are a few factors that can help:
1. The more alcohol a wine has, the more it is protected from microbial decomposition.
2. The more acidic a wine is (lower pH) the more it is protected from bacteria.
3. The screw top provides more protection against unwanted oxygen than corks ever did.
4. Good luck would help immensely.
Sounds like it’ll be one powerful brew and one heck of a challenge!