Yeast nutrients in wine making can be very beneficial when used properly. Nutrient levels in musts vary from region to region, vineyard to vineyard, and even row to row within a vineyard. Nutrient level also varies between varieties.
Nitrogen is necessary for protein synthesis. If yeast do not have enough nitrogen for protein synthesis, then they can’t adequately multiply and the subsequent fermentation will be problematic. Nitrogen levels vary dramatically in must but testing nitrogen levels is expensive and not practical for small wine makers. Use of a broad spectrum yeast nutrient and diammonium phosphate can ensure adequate amounts of nitrogen for proper yeast function.
Minimum Free Amino Nitrogen (FAN) content of must has been cited to be as low as 140 mg/L and optimum levels have been cited to be as high as 500 mg/L. Red grape must (when fermented on the skins) typically have adequate levels of FAN. However, white grape must that has been clarified prior to fermentation can lack adequate levels of FAN.
Nitrogen additions should be spread out over the course of the fermentation. To ensure that the available nitrogen sources in the must are utilized first, nitrogen should not be added until fermentation is under way. A broad spectrum nutrient should be added 24 to 48 hours into the fermentation. Diammonium phosphate should also be added 24 to 48 hours into the fermentation but can also be dosed again later in the fermentation if it is suspected that FAN levels are low.
Yeast require minerals in trace amounts for basic cellular function as well as for growth. Minerals function as osmoregulators, enzyme catalysts, enzyme stabilizers, and as regulators of physiological control mechanisms. The most important minerals for proper cellular function are: phosphorous, sodium, potassium, magnesium, manganese, calcium, and zinc.
Each mineral is needed in very specific amounts. Must will typically have a fairly good mineral content, but some minerals can be lacking. Zinc is a commonly lacking mineral that has a great effect on yeast growth. A balanced yeast nutrient, such as Wyeast Nutrient, will typically provide adequate levels of each mineral necessary.
Vitamins are necessary for metabolism but the needs are strain specific and vary widely. Vitamin content in must varies widely depending on vineyard location, grape variety, vineyard management techniques, and the particular year.
Vitamins that are necessary for yeast function are: Biotin, Thiamin, Pantothenic acid, Nicotinic acid, Inositol, Pyridoxine and Riboflavin. Must that is lacking in any of these compounds can be subject to problem fermentation. Typically a shortage of a given vitamin will cause a prolonged fermentation with production of off aromas such as sulfur compounds. Vitamin shortages can cause stuck fermentations or high residual sugar contents.
Use of a balanced yeast nutrient, such as Wyeast Nutrient, will provide adequate levels of vitamins for proper yeast function.