Nitrogen in Grape Berry and Wine

Nitrogen in the Growing Grape Vine
The importance of nitrogen in the growing vine:

• lack of nitrogen can halt growth and development of the vine
• an excess can increase the vigour, prolong growth, delay maturation
• an excess can favour the development of mildew and rot and decrease the level of anthocyanins and tannins in the berry
• an excess is detrimental to sugar accumulation in the berries during ripening

Mineral nitrogen in the form of NH4+ can represent up to 80% of the total nitrogen before véraison but it decreases to 5-10% after maturation and decreases even further after fermentation of the must .
Nitrogen in the Must and Wine

• total nitrogen in the must can vary from 100 to 1200 mg/L, and usually red wines possess higher nitrogen content than white wines.
• nitrogen in the must is called fermentable nitrogen and used by yeast to carry on normal alcoholic fermentation
• total amino acid content can vary widely, from 300 to 5000 mg/L, and represents about 20-50% of the total nitrogen in the must
• the must contains about thirty amino acids, but only around seven are present in quantities above 100 mg/L: proline, arginine, glutamine, alanine, glutamate, serine and threonine.

• when fermentable nitrogen is below 150-200 mg/L, ammonium (in the form of phosphate, sulphate or sulphite salts) is added to the must to avoid “stuck” fermentations and formation of hydrogen sulfide and other sulphur odors
• ammonium consumption by yeasts results in a greater acidification of the media than amino acids consumption
• wine is generally less rich in amino acids than the initial must it is derived from
• by-products of yeast amino acid metabolism include precursors for the synthesis of aromatic compounds, such as isoamyl acetate, isovaleric acid and isobutyric acid and their ethyl esters, as well fusel alcohols and methionol
• urea originates from arginine and is a precursor of ethyl carbamate, a known carcinogen
• wine also contains biogenic amines, such as histamine, tyramine, putrescine, cadaverine, spermidine and spermine, which are formed mainly during the malolactic fermentation from amino acids present in the must
• biogenic amines can cause problems for some consumers: histamine can cause headaches, hypertension and digestive problems while tyramine can be associated with migraine and hypertension
Proteins:

• amino acids can also be present in polymerized form, such as small oligopeptides of 2-4 amino acids to large proteins of up to 150,000 Da in size
• proteins are present in widely varying quantities in the must and wines
• proteins are present in concentrations ranging from 15 to 230 mg/L
• proteins can also contribute to the development of problems in the fermentation of white wines due to exposure to cold, heat or cold-heat temperature variations
• proteins are are largely absent in red wines due to the precipitation of proteins with tannins
• the organoleptic effect of proteins on wine aroma can be considered negligible
• the protein content is also of economical importance because it greatly affects the clarity (translucency) of the wine
• proteins are usually precipitated from the wine by addition of bentonite

Other blogposts that I've written about nitrogen and proteins:

• The Importance of Nitrogen in Wine Fermentation
• Grape Berry Composition at Harvest

References:
1. Carlos Conde, Paulo Silva, Natacha Fontes, Alberto C. P. Dias, Rui M. Tavares, Maria J. Sousa, Alice Agasse, Serge Delrot, Hernâni Gerós, Biochemical changes throughout Grape Berry development and fruit and wine quality, Food, 1(1), 1-22 ©2007 Global Science Books.