Yeast Nutrient should always be added when making country wines (ie wines from fruits etc) and ciders. It is added at the start of fermentation so that the nutrient will provide nourishment to the yeast. Without nutrient, yeast will stop the fermentation process and cause "stuck" fermentations. The dose rate is 1 teaspoon per gallon (4.5 litres) of wine/cider.
This nutrient uses a mix of equal proprtions of Diammonium Phosphate and Ammonium Sulphate. The combination of the 2 nutrients will provide a better feed for the yeast than a single nutrient.
The yeast nutrient provides nitrogen for essential yeast growth whilst the phosphate ensures a vigerous ferment .