Sulphur can be used in two ways in winemaking. It can be sprayed on the vines to stop rot and fungal disease. Sulphur dioxide is also used to stabilise finished wine.
The production managers of large bottling sites and quality control managers of large retailers often want to be absolutely sure that wine is stable - even in extreme conditions. This has led to a situation where large volume wines often have too much sulphur - levels that can aversely affect people sensitive to it.
Sulphur is a "natural" substance, so it can be used in making organic wine, although most organic producers work hard to use the minimum possible.
It is very rare not to have any sulphur dioxide at all added before bottling. Indeed I have experienced too many oxidised "natural wines" to advocate that all wines should be sulphur free. The most important thing is to make sure the minimum necessary is used. Up to 250 mg per litre is allowed in wines. I look for levels of 50 mg or less in all the wines we buy.
We've just shipped our first no sulphur wine. I am slightly nervous about this, but Jerome Estève at Chateau Montfin has convinced me to buy a small quantity of his Cuvée Vincent. His cellar is always spotless, his work in the vineyard impeccable. It's drinking really well now - a soft, fruity wine. I'll be sampling it regularly to check it is still good.