Sulfur dioxide

Properties

Antiseptic : inhibits micro-organisms such as yeastUnicellulaires micro-organism which induces the alcoholic fermentation of must/juices. and bacteria.

Anti-oxidant : Avoids the oxidation of molecules, especially the oxidation of (polyphénols). Also inhibits enzymes such as laccases and tyrosinases.

Sulfur dioxyde is present in different states depending on the wine/juice parameters. It can be separated into 2 fractions : an active one, called Free SO₂ (SO₂F) and an inactive one, Combined SO₂.

The efficiency of the active fraction on wine/juice parameters depends on 3 factors : ABV %v/vIt represents the alcool quantity in a specific volume solution., temperature and pH. This fraction can also be separated in 2 more fractions, a strongly active one which represents the anhydride sulfide H₂SO₃, called active / molecular SO₂ (SO₂A) and the bisulfide ion HSO₃^-.

Before fermentation

This will help you to evaluate the potential of the grapes and to adjust the SO₂ quantity before starting the fermentation process.

You need to add g/hL of SO₂ before starting the fermentation.

In case you have to put more than 10 g/hL, getting a very fine wine could be quite difficult.

Even if the grapes look good, please keep at least 3 g/hL SO₂ to avoid any oxidative yeast spoilage.

Vins	Concentration sucres (=glucose+fructose)	CE 606/2009 (mg/L)	BIO UE 203/2012 (mg/L)	Zone
Rouges	sucres < 2 g/L	150	100	/////
	2 g/L ≤ sucres < 5 g/L	150	120
	sucres ≥ 5 g/L	200	170
Blancs/rosés	sucres < 2 g/L	200	150
	2 g/L ≤ sucres < 5 g/L	200	170
	sucres ≥ 5 g/L	250	220
Doux	TAV > 15% sucres > 45 g/L	300	270	Vins de pays deFranche-Comté, Coteaux de l’Auxois, Saône et Loire, Coteaux de l’Ardèche, Collines rhodaniennes, Comté Tolosan, Côtes de Gascogne, Gers, Pays du Lot, Côtes du Tarn, Pays de Corrèze, L’île de beauté, Pays d’Oc, Côtes de Thau, Coteaux de Murviel, Val de Loire, Méditerranée, Comtés rhodaniens, Côtes de Thongue, Côtes Vermeille.
Moelleux	Vins blancs Botrytisés/passerillés	300	270	Issus des AOPBordeaux supérieur, Graves de Vayres, Côtes de Bordeaux-Saint-Macaire, Premières Côtes de Bordeaux, Côtes de Bergerac, Haut Montravel, Côtes de Montravel, Gaillac, Rosette et Savennières.
Liquoreux	Vins blancs Botrytisés/passerillés	400	370	Issus des AOPSauternes, Barsac, Cadillac, Cérons, Loupiac, Sainte-Croix-du-Mont, Monbazillac, Bonnezeaux, Quarts de Chaume, Coteaux du Layon, Coteaux de l’Aubance, Graves Supérieures, Sainte-Foy Bordeaux, Saussignac, Jurançon sauf si suivie de la mention «sec», Anjou-Coteaux de la Loire, Coteaux du Layon suivi du nom de la commune d’origine, Chaume, Coteaux de Saumur, Pacherenc du Vic Bilh sauf si suivie de la mention «sec», Alsace et Alsace grand cru suivie de la mention «vendanges tardives» ou «sélection de grains nobles».
Vins de liqueur	sucres < 5 g/L	150	100	/////
Vins de liqueur	sucres ≥ 5 g/L	200	170	/////
Effervescents de qualité	sucres < 2g/L	185	135	Champagne
Effervescents de qualité	sucres ≥ 2g/L	185	155	Champagne
Effervescents	sucres < 2 g/L	150	100	Crémant
Effervescents	sucres ≥ 2 g/L	150	120	Crémant
Autres effervescents	sucres < 2g/L	235	185	Cuve close
Autres effervescents	sucres ≥ 2g/L	235	205	Cuve close

Optimization

Table 1 : A simple units converter, switch between g/hL, g/L, % (w/v) and mg/L.

From	To

Table 2 : Evaluate SO₂Active percentage. Find the right amount of free SO₂ to add depending on the percentage of Active SO₂. This tool is extremely useful to reduce the quantities usually used during the ageing process.
If you are really confident and already know what SO₂A concentration is required, please use the last line and enter your concentration. The table will give you the equivalent depending on your previous wine parameters but be careful and stay below 2 mg/L SO₂A (detection threshold).

ABV (% v/v)	Temperature (°C)	pH	Current SO₂F (mg/L)

SO₂A (%)	SO₂A (mg/L)

SO₂F reds [0,35 mgSO₂A/L]	SO₂F anti-brett [0.6 mgSO₂A/L]	SO₂F whites/rosés [0,65 mgSO₂A/L]

SO₂F residual sugars [1,2 mgSO₂A/L]	SO₂F mutage [1.5 mgSO₂A/L]

Personal dose SO₂A (mg/L)	Personal dose SO₂F (mg/L)

Table 3 : Calculate required concentration Calculate the amount of free SO₂ necessary depending on your stock solution properties (Please refer to the label's product or your supplier for further information).

The combined rate is extremely important for evaluating how active the SO₂F is, especially with juice from noble rot grapes. It is also highly recommended to know this rate before proceeding to a mutage. To calculate this rate, measure the SO₂F 24-48h after adding a known concentration of SO₂T. Repeat this test at least 3 times and average the results : (SO₂F_final - SO₂F_initial) / SO₂T_added. The default table value is 2/3.

Current SO₂F (mg/L)	required SO₂F (mg/L)	Combined rate

Wine volume (hL)	Stock solution

Required quantities

SO₂T	SO₂T	Potassium Metabisulfite	Stock solution

Table 4 : Remove SO₂ by using hydrogen peroxyde (H₂O₂)

Adding hydrogen peroxyde will oxidise the SO₂ in sulfate ions which will reduce the SO₂ level in wine.

Always keep a 10% error margin for the ideal SO₂ concentration to remove (Example : Get rid of 20mg/L ? Start with [20 - 0.1 * 20 = 18 mg/L]).

It is highly recommended to do a lab trial before adding this product. You can use our tutorial to help you.

This substance needs to be added extremely slowly into the wine. Be sure to mix the tank during addition to avoid any localised oxidation.

After addition, measure the new SO₂ level and adjust.

SO₂ concentration to remove (mg/L)	Wine volume (hL)	Concentration stock solution (%w/w)

Stock solution quantity required	Stock solution volume required

Tips

Decreasing the temperature will increase sulfur dioxide and oxygen dissolution.

1 mg/L of dissolved O₂, will oxidize 4 mg/L of free SO₂.

During alcoholic fermentation, it is recommended to measure the SO₂ level between 1050 and 1030.

Decreasing SO₂ doses

A sterilizing filtration (tangential for high turbidity juices) at the end of the fermentation process will strongly reduce the number of micro-organisms.

A flash pasteurization will sterilize the grapes.

At the end of the fermentation, a drastic drop down to around 6°C will lower the activity of micro-organisms.

Adding nitrogen especially before fermentation, will decrease ethanal concentration which will reduce combined SO₂.

Adding thiamine (B1 vitamin) at the beginning of the alcoholc fermentation decreases part of the wine coumpounds involved in the formation of combined SO₂.

Lysozymes inhibit gram+ bacteria activity (lactic).