Potassium metabisulphite (K2S2O5) is adding for sulphate of grape mash (crushing of grapes), must and wine. To some extent the process is an analogue of sulphate with sulphurous acid. It is easily soluble in hot water and more difficult soluble in must. Theoretically it contains 57,66 % sulphur dioxide but for practical usage is assumed to contain 50 % sulphur dioxide by its weight. For that reason in determining the desired dose of sulphur dioxide we have to use twice as much potassium metabisulphite.
For example: we have 100 kg of grape pulp which has to be ferment and we want to be sulphated with a dose of 60 mg/kg SO2
MSulphur dioxide = 60.100/1000 = 6 g
It is known that 1 g potassium metabisulphite releases about 0,5g SO2, for dose 6 g SO2 is necessary to add 2.6 = 12 g potassium metabisulphite.
Direction for use of potassium metabisulphite:
The calculated and measured quantity of potassium metabisulphite is dissolved in some warm water. You can add a little grape must and then mix it and add it to the tank for fermentation or vessel for storage of wine.
Adding sulphur tablets
Sulphur tablets are soluble and their active ingredient is potassium metabisulphite. It allows quick and easy sulphating. Each tablet contains about 67 % of its total mass potassium metabisulphite, if the mass of one tablet is 5 g it contains about 3,35 g potassium metabisulphite. The tablets are easily soluble in grape must or wine and can be added directly to the fermentation tank or vessel for storage of wine, therefore do not require any preparation.
For example: we have 100 kg of grape pulp which has to be ferment and we want to be sulphated with a dose of 50 mg/kg SO2
MSulphur dioxide = 50.100/1000 = 5 g
It is known that 1 g potassium metabisulphite releases about 0,5 g SO2 , for dose 5 g SO2 is necessary to add 2.5 = 10 g potassium metabisulphite.
Each 5 g sulphur tablet contains 3,35 g potassium metabisulphite , for dose 10g potassium metabisulphite which contains 5 g SO2 we must to use 3 tablets.
Note: examples are given for 100 kg grape pulp without clusters. The average percentage of participation clusters in the mass of grapes is about 3 % as the exact value depends on the variety of grape.