4.1.2.b Sulphite management

What are the advantages of sulphiting when the harvest arrives?

Sulphur dioxide has many properties: it is an antiseptic, antifungal, antioxidant and solvent. In wine, we refer to free, combined, total or active SO2.

Here are some basic definitions of these terms:

• Free SO2: sulphites that are not bound to other molecules and which are active with respect to oxygen.
• Active SO2: the molecular fraction of the free SO2. It is the most active form, especially with regard to microorganisms. Its content varies according to temperature, pH and ABV.
• Combined SO2: the fraction of sulphites linked to other molecules in the wine such as sugars or aldehydes.
• Total SO2: the sum of the free and combined SO2.

Usage is no longer systematic and doses have been drastically reduced. However, it is still used in certain cases on the arrival of the harvest at the winery for several reasons:

• It inhibits the development for microorganisms causing spoilage and allows the selection of Saccharomyces-type yeasts that are more sulphur-tolerant. This makes it possible to carry out fermentations with indigenous yeasts more safely.
• In the case of botrytized grapes, sulphiting inhibits laccase (an oxidation enzyme).

When is it possible to do without it?

The key to sulphur-free winemaking is a healthy, ripe harvest. Several parameters make it possible to manage a sulphur-free vinification:

• Very rigorous selection when the harvest enters the winery to eliminate all poor-quality berries, leaves and possible sources of botrytis
• A good inerting system starting at vatting until the onset of fermentation to avoid any deviations
• An efficient thermoregulation system to start the fermentation quickly when the time comes (whether or not there has been a cold maceration period)
• Preparation of a fermentation starter vat or to proceed using inoculation to rapidly initiate fermentation. This last step is optional but ensures smooth fermentation.

As an example, Domaine d'Eugénie has been vinifying without sulphur for 5 years now. This requires more monitoring and increased vigilance compared to more traditional vinification. In the majority of cases there is no inoculation or fermentation starter vat but rigorous inerting and the monitoring of temperatures are very important.

How much should be used and in what form?

A typical dose ranges from 0 to 8 g/hl. In general, a maximum of 4 g/hl is used when necessary. The most practical form to use at this stage is the liquid form (potassium bisulphite, potassium metabisulphite, etc.).