The 500g Sodium Metabisulphite is used before you start your homebrewing, it is used to clean and steralise all your equipment, this prevents from any bacteria forming or any impurities that would spoil the brew. Just add water to a small amount of sodium metabisulphite and use in a well-ventilated area, then you\'ll be ready to start your brewing! Sodium Metabisulphite Features Youngs Sodium Metabisulphite 500grm Tub/4069 Used to clean and steralise home brewing equipment Just add water and use small amount Use in well-ventilated area Youngs\' Ref. MPN: 4069Colour: WhiteSizes: 500gPM Ref: 542036