Is sulphite the only preservative used?
No. Some winemakers add potassium sorbate at the end of fermentation. This forms sorbic acid in the wine, which is a yeast inhibitor. You don’t need it in dry wines, but it can be used to prevent intended semi-sweet or sweet wines from continuing to ferment past the desired end point. Note that sorbate is genuinely a preservative, whereas sulphite is technically a retardant but still an active part of the winemaking and maturing process.
