Why add Sulphur Dioxide Sulphur?

Dioxide SO₂ is a chemical compound additive that is used in winemaking to prevent oxidisation of the juice and also to prevent spoilage microorganisms such as the vinegar bug, from contaminating  the winemaking results. It has been used for at least the last 75 years in winemaking and nothing else, despite considerable research by oenologist's,  has proven as effective to avoid spoilage..  In part, it does naturally occur during the fermentation of the grapes, so can be considered a natural additive, insuring the grapes against deficiencies that could render the wine undrinkable.

The addition of sulphur dioxide early in the winemaking process, at the grape processing stage,  is done to suppress bacteria and wild  yeast on the grape skins, prior to adding a pure cultured strain of yeast to take over the fermentation. Research has shown that quality wines are made when SO₂   has been used both before and at the end of the winemaking process.

Reliance on 'wild yeast' for the fermentation will in most cases render the wine undrinkable. Most likely the wild yeasts will die before the fermentation is complete, leaving  you with a stuck fermentation, low alcohol wine that is destined to fail or leave you with a vinegar taste to your wine.

How to obtain Sulphur Dioxide

Sulphur Dioxide ..SO₂  is available as a white powder called Potassium Metabisulphite.

Sodium Metabisulphite is also a source of SO₂   but as it is a cheaper option it should be used primarily for the sterilisation of equipment only

SO₂  is also found in Campden Tablets, which are commonly used by home winemakers because of the convenient tablet form.  

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Why SO2 is so crucial in the WHITE white winemaking process.  

While adding SO₂  in either red or white wine making is important, the step of adding it in white winemaking is crucial as white juice oxidises more easily than red juice.  This oxidisation process can cause the juice to brown, at the early crushing stage as well as the maturing bottle stage. This can be accelerated in warm conditions, so it is important to process white wine grapes as quickly as possible and handle the juice in as cool temperatures as possible.

Dosage rate:

For grapes that are free of mildew or mould,  the usual dosage rate is between 50 to 100 ppm (parts per million). j This is approximately  1 teaspoon per 10 gallons (approx 40 litres)  of juice or must.  It can be added by mixing into a small amount of juice and adding this back to the bulk and mixing thoroughly.