Sulphur in wine

Sulphur in wine

At the risk of rendering you so bored that you want to punch yourself repeatedly in the face, I'd like to write a bit about sulphur dioxide in wine. It can be an intensely dull subject, but it's useful to be aware of if you want to understand more about how wine is made, or if you're curious about what makes 'natural' and 'low-intervention' wines different from industrially made ones. Also, I get the sense that, because few people actually see what goes on in a winery cellar, there's a lot of confusion about what it does.

So here goes. Good luck everyone...

What is sulphur dioxide?
Sulphur dioxide then. In a wine context you might also hear it referred to 'SO2'. Sulphites (Eng)/ sulfites (US) are the group of sulphur-based compound of which sulphur dioxide is one example. Sulphites/sulfites are different from sulphites/sulfides or sulphates/sulfates, which are a different kettle of worms altogether and would tip us well over the self-punching boredom threshold if I was to try and define them. 

For present purposes I'm going to use 'sulphur' for short. Sulphur's main use in the context of food and drink is as an anti-bacterial agent and an antioxidant - it stops chopped fruit from discolouring, and is used to preserve everything from dried fruits to sausages.

What has it got to do with wine? 
Sulphur has been a more or less essential part of winemaking since at least the 1st century CE, when Roman naturalist Pliny the Elder wrote about sulphur candles being used to fumigate casks for wine (that still happens to this day). You’ll find sulphur, usually in the form of powdered or liquid potassium bisulphate, in 99.8% of wine cellars - whether they're winemaking behemoths churning out mass-market wine or one-man shows producing a 1,000 bottles in a shed.

For a winemaker it's extraordinarily useful: it's important in the vineyard, where it helps to curb common fungal diseases like oidium (powdery mildew); in the cellar, where it's used as a disinfectant when cleaning equipment and barrels; and in the winemaking process: on grapes coming into the winery to prevent oxidation, and in the wine to prevent oxidation and kill spoilage bacteria (eg, those responsible for volatile acidity, brettanomyces and mousiness).

Pliny the Elder, or maybe the Younger. One of the two (NB: in one of my lonelier lockdown moments I started dabbling with the 'liquefy' function in PhotoShop).

Will it give me a headache?
You are more likely to have a headache after drinking a supermarket wine than a natural/low-intervention one - and that's got a lot to do with sulphur levels. Several recent scientific studies have shown that sulphur inhibits the action of a liver enzyme which does a crucial job in metabolising alcohol.

This enzyme, glutathione, helps to convert acetaldehyde to acetate, which is easily excreted by the human body (the metabolic process for alcohol goes: alcohol-acetaldehyde-acetate). When acetaldehyde is not broken down, or is broken down more slowly - that's when you'll feel like a pig shat in your head. That's because acetaldehyde is up to 30 times more toxic than alcohol. Wines made with minimal/no sulphur won't totally liberate you from the pain of a hangover, but there's a good chance it'll be less of a problem. 

A word on allergies: most people who say they're allergic to sulphur are just being neurotic. Reportedly only 1% of people have an allergic reaction to sulphur and for 99% of us, it’s harmless.

'I feel like a pig shat in my head...' (Withnail & I, 1987)

Sulphur is a winemaker's best friend...
A small number of very zealous winemakers (and wine drinkers) think adding sulphur to wine is sacrilege, but the vast majority - even most natural winemakers - would admit they couldn't work entirely without it. Even at very low concentrations in the winemaking process, it does an amazingly nuanced job: as an anti-oxidant it can bind not just with molecules that cause oxidation, but also its end products, like acetaldehyde – so it's not only able to limit the oxidation process but also, up to a point, clean up the mess after it’s happened. As an anti-bacterial agent, it can work selectively, preventing undesirable bacterial growth while allowing the right yeasts to do their job. 

Undesirable bacterial growth

Sulphur is present in all wines - even 'natural' wine... 
As well as being a product that's added to wine, sulphur is also a by-product of fermentation, so all wine contains a small amount. Any food/drink product containing more than 10mg/l has to carry a health warning, and since typically 10-15mg/l can be produced by fermentation, all wine labels - even those for wines that haven't had any sulphur added to them - say 'contains sulphites'.

'Ah well, if sulphur is in all wine, what's the point in bothering with natural/low-intervention wines? Why not just stick to Campo Viejo from the offie and get on with my life?'

It's a fair question. All I would say is that, in my experience, all other things being equal, the difference between a wine that contains 10mg/l of SO2 and one that contains 100+ mg/l - in terms of smell, taste, expression and, for want of a better word, aliveness - is palpable. In high doses, it can stun a wine - muting its aroma and flavour, halting its evolution and killing all the good bacteria that can make wine so interesting and multi-layered.

If you'll permit a topical football analogy, it's like the difference between playing a Premier League match in front of a crowd and playing behind closed doors. So leave that Campo Viejo alone.

Leave it alone

Beware of the dogma 
But for every 'naturalist' who argues that adding sulphur kills a wine, there are 20 ‘conventionalists’ who view ‘no-added-SO2’ as a recipe for a bacterial mess. A lot of the time, wines made without sulphur are a bacterial mess - and taste like it. You have to be pragmatic, rather than dogmatic, about it.

One thing I have learned from a long career of drinking wine and a nascent one of making it is that the less sulphur you can use (without messing up your wine), the better. Skilled, experienced low-intervention winemakers might use 5-10mg/l per application; the upper limit in the EU is about 150mg/l/ In the 1990s it was 250mg/l.

The natural wine zealots would do well to remember that there isn’t one 'no-added-SO2' producer out there who's wines are always free of faults. Sooner or later they will come a cropper due to difficult vintages, vine diseases, dodgy barrels, etc. 

For several years Victoria Torres, who I worked with in La Palma, has gradually been reducing the levels of sulphur in her wine. Her wines (and those I made with her) contain about 10 times less than your average supermarket bottle.

Lazy winemaking 
The use of higher levels of sulphur is to an extent justified in industrial winemaking. If you've just made 250,000 bottles of a wine you don't want to be worrying about bacterial problems and secondary fermentation in bottle when you can just blitz the wine with 150mg/l of sulphur and go about your day whistling, do you?

But over-use of sulphur can cover a multitude of winemaking sins. The fact is that to be able to use low levels of sulphur you need to be doing all sorts of other things right: farming organically, only using perfectly healthy (and low pH) grapes, working with things like skin maceration and lees contact to help to naturally stabilise your wine, focusing on cellar hygiene and having the right microbial environment, and generally working with the utmost care and sensitivity as the wine ferments and ages. Not everyone is prepared to do that.

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