The Wine Pages: Homebrew winemaking
In the UK we spell it Sulphite. We say Sodium metabisulphite and potassium metabisulphite. The rest of the english speaking wine making world spells it Sulfite. I am going to stick to sulfite, as a believe the international body that decides this sort of thing, has decreed that chemicals should be spelt this way.
Ever since we all started winemaking, we've been chucking in the famous Campden tablets to our wine. Virtually all wine making on the planet for the whole of recorded history have added sulfites to wine. It isn't anything new - and it isn't anything to worry about. People who do worry about it should bugger off and drink water. After sugar, yeast and acid, sulfite is probably the most important thing to get right in winemaking. Its proper control marks the difference betwen a good winemaker and a great one.
Sulfites in wine making take the form of sodium metabisulfite or potassium metabisulfite. The purpose of these chemicals is a handy method of adding sulfur dioxide gas to the wine. The amount of sulfur dioxide gas dissolved in the wine is commonly called the level of sulfites, or sometimes referred to as SO2.
What does this addition of sulfites in the winemaking process do? Primarily two things.
It kills stuff. Unwanted yeasts and bacteria cannot survive in a sulfited must - however, modern cultured yeasts are quite resistant to sulfites. So we often add sulfite to the must, leave it for a day to kill all the badies, and then add our chosen yeast. We can also use a solution of sodium metabisulfite as a sterlising agent.
It prevents oxidization This is really important. When oxygen gets dissolved into wine, it does nasty things to the wine. To prevent this, we add sulfites. This takes the place of oxygen and prevents oxidization. Therefore it is critical to keep a certain level of sulfite in the wine at all stages to prevent this.
Too much sulfite in the wine will make it smell and taste of sulfite. Nasty. So you need to be careful.
The easist way of keeping control of the level of sulfite is to start off, and maintain a level of about 30-40mg/L sulfite in the wine. When bottling, especially if you intend on keep the wine for more than 6 months, aim for about 50mg/L.
How much do we add. The famous Campden tablet is about 0.44g of metabisulfite. This is enough to raise one imperial gallon (4.5 litres) to a level of about 50mg/L. Often refered to as 50ppm. So if you start off your must with the addition of 1 campden tablet per gallon, and add another tablet somewhere during the final racking and bottling process, you won't go far wrong.
It is far far cheaper to buy a bag of sodium or potassium metabisulfite and use a pair of scales to measure it. 1kg of metabisulfite and some cheap scales will set you back about £10 on Ebay. That is a lifetime supply of campden tablets!
To measure the level of sulfite in wine, you need a kit. The Vigo Sulfoquick kit is quite expensive, but does over 200 tests and is quick and easy to use. At different stages of the winemaking process - mainly on first racking and on bottling, make sure that the sulfite level is over 20ppm but no more than 50ppm. The Femsoft sulfite calculator is a useful tool as well.
Sulfite is activated by acid. So a solution of metabisulfite and citric acid makes a powerful sterilizer. When preparing bottles I fill one bottle with hot water, and a teaspoon of each. I use a funnel to pour from one bottle to the next, a brief rinse and a drain, and they are ready.
Potassium or sodium metabisulfite. I do not know the technical side, but I've always been told to use potassium metabisulfite when adding to wine, but keep the cheaper sodium metabisulfite for sterilising bottles etc.
Wine can be made without sulfites entirely (although small amounts are generated naturally by the fermentation process) but it is hopeless and the wine does not keep for long.
All your glassware plastic fermentors should be kept sterile by adding some water and a tip of a teaspoon of metabisulfite and then sealing with a bung. It is a joy to know that whatever carboy or demijohn you reach for, it is always going to be clean and sterile.