Sulphites (the French spelling) refers to the addition of Potassium Metabisulphite to wine, creating sulphur dioxide, which has powerful antioxidant and anti-microbial characteristics. It is completely unrelated to the use of sulphur as a fungicide in the vineyard.
The anti-microbial action inhibits both harmful bacteria and spoilage yeasts. This helps prevent the wine from developing vinegary flavours, produced by acetic-acid bacteria. Spoilage yeasts may come from wild yeast in the vineyard and yeasts living in and on winery equipment. They can give wines a “mousy” aroma and other strange smells like mothballs or a sweaty horse.
Wine yeasts, which may be either wild or added by the winemaker, are more immune to sulphur dioxide. Therefore the addition of sulphur dioxide to juice will favour the growth of the “good” yeast strains desired by the winemaker.
Oxidation of wine can cause a number of faults. It can suppress desirable varietal aromas, such as that of Sauvignon blanc, therefore making the wine smell dull. Oxidised white wines can develop unpleasantly high levels of pineapple or bruised apple aromas.
In red wines, oxidation makes the wine smell and taste flat. like a bottle that has been left open for too long. The addition of small amounts of sulphur dioxide can produce fresher aromas by reducing the level of acetaldehyde, which gives wine a Sherry aroma. It also helps to maintain colour stability, preventing wines from going brown over time.
Why would winemakers want to promote wines made without sulphites?
The main reason is to promote the wine as being more “natural” or free from additives. Sulphur dioxide can cause asthma attacks in sulphite-sensitive individuals but only about 0.4% of the population are allergic to sulphites. However, many people believe that they could or do suffer adverse effects from sulphites in wine, particularly migraines.
There is plenty of false information on the internet to support that idea and the market for sulphite-removal tablets and gadgets is huge. These hydrogen-peroxide tablets and aerators or wands don’t remove sulphites, they simply add oxygen to the wine, which binds up any free sulphur-dioxide. The amount of sulphite in the wine remains the same.
The level of sulphur dioxide in wine is strictly controlled and limited to safe levels. In the EU, red wine can contain no more than 150mg/L and white wine 200mg/L. On average, French red wine contains around 60 and white wine around 90.
There has been no scientific evidence that sulphites cause headaches. In fact the idea that “red wine headache” is a result of sulphites is in contrast with the fact that white wine generally contain 50% more sulphites than red.
Based on animal testing there are no adverse effects of sulphites up to a daily intake of 70mg per Kg of bodyweight therefore the WHO recommend an acceptable daily intake of 0.7mg per Kg of body weight. Acceptable levels are always set 100 times lower than the safe limit. So an 80Kg human can drink a bottle of wine a day without any concern about the sulphites (the alcohol might be another matter).
The fermentation process of wine produces somewhere between 10 and 30 mg/L of SO2 naturally. So even wines with no added sulphites will still contain some. The law states that any amount over 10mg/L means that the words “Contains Sulphites” must be written on the label (don’t ask me why). So even Natural wines with no added sulphites may still carry this warning.
In general, higher-quality, smaller-production wines contain lower levels of sulphites than cheaper commercial wines because there is no need to add sulphites to clean, healthy grapes until the end of fermentation.
Many organic, sustainable and artisanal producers will have sulphite levels around half that of cheaper brands.
Adding too much sulphite can give a “struck match” aroma to white wines and make red wines “closed” and less aromatic
Fans of Natural wine say they like them because they feel more “alive”.
Sulphites are a tool to help winemakers make enjoyable and long-lasting wines. Like in many things, moderation is better than total avoidance. High levels of sulphites are only required to try to fix a poor wine made from diseased fruit or from errors in the winery.
A wine made with judicious amounts of sulphites, added at the appropriate time, will avoid any of the faults that can result from oxidation, bacterial or yeast spoilage and yet keep the wine feeling open and alive.
I believe that the trend for “Zero sulphite” wine is mainly founded on the false premise that the sulphite level of wine is responsible for various side effects.
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