Sulphur is one of Earth’s elements and its primary use in viticulture is to prevent and control powdery mildew infection, which is one of the most prevalent risks to vineyards. Mildew is a fungus, which can be seen on the leaves or on grape clusters as a white or grey powder. It is important to protect vines, even before mildew has become apparent, which means sulphur is applied at regular intervals. It is distributed in either a liquid or powder form, where it can be seen as a yellow/green dust on the vine. Usually it is applied every 7-14 days, from when the shoots are around 3 inches in length to the point when the young grapes contain sufficient sugar to prevent the mildew continuing its growth cycle.
Even though the farmer usually wears a mask and protective clothing while spreading sulphur, in its elemental form it is non-toxic and is permitted in organic farming.
Sulfite meanwhile is a compound, which is added at various stages of the winemaking process, and in fact small amounts even occur naturally as a by-product of fermentation. Once residual sugars in a fermenting wine are in line with the winemakers wishes, the addition of further amounts of sulfite is used to stop the fermentation. Later on in the winemaking process, sulfite is also added as a preservative, to protect against oxidation and bacteria growth.
Sulfite is one of the food allergens, which is why its use is seen noted on a wine label. This is necessary when there is a measure of more than 10 parts per million (“ppm”). A bottle of wine may contain up to 300ppm (Lanzarote wine considerably lower) and up to 100ppm is permitted in organic wine. Dried fruit meanwhile can contain up to 3,500ppm!