Sulphite in wine - what is it and how does it work?

Sulphur is one of the few chemical elements that even those who have never studied chemistry recognise, at least by name. In connection with wine, all kinds of things are attributed to sulphur, which is always declared on the label as "sulphur dioxide" (SO2) or "sulphite". It has to be used for many things and the natural wine movement uses it to ideologically distinguish itself from conventional wine. The addition of sulphur dioxide = SO2 = sulphite basically serves the purpose of preservation.

The history of sulphur

The use of sulphur in wine production goes back to Roman times. In ancient times, as today, sulphur was used for its antibacterial and antioxidant properties. However, at that time its use was limited to burning sulphur to clean wine containers and the practice itself does not appear to have been widespread.

The use of sulphite in wine in other, more easily dosed forms, however, dates from the modern era. Until well into the twentieth century, the use of liquid SO,solutions, now the most common in Burgundy, was confined to large, industrial wineries, as their production was harmful and laborious. The heavy dosage of sulphite in wine was then reserved for damaged or spoilt harvests and/or the production of ordinary table wines.

If in the 1980s some pioneering natural wine winemakers:in began to draw attention to sulphites, it was because the addition of sulphites in winemaking, once limited to burning sulphur during racking, now governs the entire winemaking process.

Oenologists prescribe it at harvest, at bottling and everywhere in between. Winemakers adhered to it to take advantage of the burgeoning export market and to ensure stability during transport.

The excessive addition of sulphite quickly became a crutch of modern winemaking. It began to define the taste of wine for much of the drinking public.

Sulphites in the wine glass

How do we perceive sulphite in wine? Excessively sulphated wines announce themselves by an astringency, a bleached out quality that sometimes creates a feeling of tension in the nose. On the palate, the flavours and textures appear simplified and rigidly outlined. On a primal level, the wine becomes unappetising: you don't feel like taking another sip.

The more natural wine you taste, the more you notice the excessive addition of sulphite. Many long-time tasters of natural wines report that they are becoming increasingly picky about what level of sulphite they consider tolerable. What you once perceived as the normal aromas and flavours of a Chablis may one day turn out to be the bland, tart profile of a white wine overly laced with sulphite.

Can you be allergic to sulphite in wine?

Allergic sensitivity to sulphites does indeed exist. However, severe allergic reactions to sulphites are extremely rare. The most common symptoms of an allergic reaction to sulphites are asthma-like and include wheezing, coughing and chest tightness.

Do sulphites in wine cause headaches? Or worse hangovers?

There is no scientifically proven link between sulphite levels in wine and headaches or a bad hangover. Research on wine-related headaches has instead considered histamines and phenolic flavanoids - compounds more likely to be found in red wines, which tend to have lower sulphite levels than white wines. However, sulphites are known to enhance the allergic effects of histamines, so there could be an indirect link.

In any case, most of us can confirm from our own experience that we feel worse about highly processed wines. But is this reaction due to the high sulphite content or to the many other additives regularly used in the production of such wines?

However, many common foods contain more sulphites than wine. Are sulphites harmless then?

This is a misleading simplification of how our bodies work. For one thing, no measurable compound we ingest arrives in isolation (think of the interaction between sulphites and histamines mentioned earlier). We don't know if or how sulphites consumed as an ingredient in wine have a different effect than sulphites consumed as an ingredient in dried apricots or bacon.

How are sulphites added to wine?

The most radical natural wine winemakers do not add sulphites at any stage of winemaking.

However, in the more pragmatic wing of the natural wine scene, it is common to add tiny amounts of sulphites, often after malolactic fermentation and racking (see page 103) or during assemblage before bottling (see page 105). Sulphites can be added to wine in various forms. Here are the most common.

Sulphur wicks

Sulphur wicks are burned inside barrels to prevent and remove bacteria build-up between uses.

(In the past, they were also used to preserve wines during bottling, but this use became obsolete in the early twentieth century due to other methods that allow more accurate dosing.) Over-zealous treatment with sulphur wicks can lead to a significant addition of sulphite, which affects the wines stored in these barrels. Most natural winemakers avoid treating barrels and other wooden vessels with sulphur wicks more than once a season, and some do not do so at all. (By comparison, conventional Burgundy estates burn sulphur wicks in their empty barrels up to once a month).

Liquid sulphur dioxide

Among natural winemakers who add sulphites, sulphur dioxide solutions are the most common form of sulphite addition because they are so easy to dose. Dilutions of 5 or 10 percent are common.

Ammonium bisulphite, potassium bisulphite or potassium metabisulphite

These agents are available as powders or tablets.

They can be sprinkled directly on the crop or added to barrels or tanks. Ammonium bisulphite is rarely used by natural winegrowers as it is not permitted for organic wine under EU legislation.

Sulphur dioxide gas

Sulphur dioxide pressure vessels are used to add sulphites to wines. In Muscadet or Moselle, for example, sulphur dioxide gas is used to stop malolactic fermentation (see page 103). In the natural wine scene, this method is rarely if ever encountered.

Volcanic sulphur

Many supporters of biodynamics believe that mined volcanic sulphur is different from "manufactured" sulphur produced by petroleum refineries. Although chemically they are the same element, they are believed to have different energies. Therefore, some winemakers use volcanic sulphur by burning it and piping the vapours into the wine tanks. The use of volcanic sulphur is technically illegal because its natural state is not chemically pure. Its use is also controversial because of the poor working conditions to which the miners are subjected when extracting the sulphur.