Natural wine preservatives and good wine making practice 

The chief preservatives in wine are alcohol and tannin. Both are entirely natural. There are very few organisms which will survive immersion in alcohol. It has therefore long been used as a sterilant in medicine. Alcohol is much more stable in wine than sulphur dioxide. It can be attacked by vinegar producing bacteria, but these organisms need air. Other factors will assist to render the use of additional preservatives unnecessary. These factors include:

• Careful harvesting by hand to avoid damage to the grapes.
• Speed of movement between vineyard and winery.
• Clean conditions in the winery.
• Cool grapes at the crusher, chilled where necessary.
• A healthy fermentation.
• Regular topping of barrels to exclude air and maintenance of full tanks with a carbon dioxide cover (This gas is a natural product of yeast fermentaion).
• The use of filtration to screen out organisms which could harm the wine, especially prior to bottling.
• The presence of tannin, as in red wine, and to a much lesser extent in white.
• The use of refrigeration to prevent microbial growth in bulk wine storag.
• Good winemakers use as little SO2 as possible because they also know that sulphur dioxide produces sulphuric acid and this makes a wine taste 'hard'. Its most important use in winemaking is to knock back bacteria and wild yeast prior to fermentation. There are other ways to attack this problem. One easy way to do it is to harvest by hand so that the fruit does not get a chance to generate unwanted organisms before you swamp it with yeast at the crusher.

Good winemakers use as little SO2 as possible because they also know that sulphur dioxide produces sulphuric acid and this makes a wine taste 'hard'. Its most important use in winemaking is to knock back bacteria and wild yeast prior to fermentation. There are other ways to attack this problem. One easy way to do it is to harvest by hand so that the fruit does not get a chance to generate unwanted organisms before you swamp it with yeast at the crusher.

In the malolactic fermentation bacteria convert malic to lactic acid and eliminate sulphur dioxide binding compounds like acetaldehyde and pyruvic acid. Malolactic ferment disposes of one of the main reasons for the use of SO2, i.e. the chemical binding of these somewhat stale smelling compounds. The bacteria ferments them away. A good clean ferment of clean grapes in clean containers, and its removal from the influence of oxygen at the end of fermentation, produces a very stable product. The problems begin with poor containers and oxidation after ferment. Wooden barrels in warm conditions are the chief risk but there is many a winery that has ill fitting lids on their tank.

The natural preservatives are more potent, and definitely more persistent than the added chemical and it is most unfortunate that we refer to sulphur dioxide as 'the preservative'. One notes that acetobacter, the principal bacteria that takes wine to its next breakdown stage, is not inhibited by SO2. Nor is the brettanomyces yeast. Studies at the Australian Wine Research Institute confirm that acetobacter develops prolifically in bottles stoppered with cork and stored in an upright position for any length of time – even though there may be significant SO2 present. 'The Preservative' is of no use under these conditions.