This review discusses the impacts of nitrogen addition in the vineyard and winery, and establishes the effects that nitrogen has on grape berry and wine composition and the sensory attributes of wine. Nitrogen is the most abundant soil-derived macronutrient in a grapevine, and plays a major role in many of the biological functions and processes of both grapevine and fermentative microorganisms. Manipulation of grapevine nitrogen nutrition has the potential to influence quality components in the grape and, ultimately, the wine. In addition, fermentation kinetics and formation of flavour-active metabolites are also affected by the nitrogen status of the must, which can be further manipulated by addition of nitrogen in the winery. The only consistent effect of nitrogen application in the vineyard on grape berry quality components is an increase in the concentration of the major nitrogenous compounds, such as total nitrogen, total amino acids, arginine, proline and ammonium, and consequently yeast-assimilable nitrogen (YAN). Both the form and amount of YAN have significant implications for wine quality. Low must YAN leads to low yeast populations and poor fermentation vigour, increased risk of sluggish/stuck/slow fermentations, increased production of undesirable thiols (e.g. hydrogen sulfide) and higher alcohols, and low production of esters and long chain volatile fatty acids. High must YAN leads to increased biomass and higher maximum heat output due to greater fermentation vigour, and increased formation of ethyl acetate, acetic acid and volatile acidity. Increased concentrations of haze-causing proteins, urea and ethyl carbamate and biogenic amines are also associated with high YAN musts. The risk of microbial instability, potential taint from Botrytis-infected fruit and possibly atypical ageing character is also increased. Intermediate must YAN favours the best balance between desirable and undesirable chemical and sensory wine attributes. ‘Macro tuning’, of berry nitrogen status can be achieved in the vineyard, given genetic constraints, but the final ‘micro tuning’ can be more readily achieved in the winery by the use of nitrogen supplements, such as diammonium phosphate (DAP) and the choice of fermentation conditions. This point highlights the need to monitor nitrogen not only in the vineyard but also in the must immediately before fermentation, so that appropriate additions can be made when required. Overall, optimisation of vineyard and fermentation nitrogen can contribute to quality factors in wine and hence affect its value. However, a better understanding of the effect of nitrogen on grape secondary metabolites and different types of nitrogen sources on yeast flavour metabolism and wine sensory properties is still required.

Implications of nitrogen nutrition for grapes, fermentation and wine

Wine is made up of more than one thousand compounds, the majority of which, such as vitamins and minerals, come from the grapes, while others, like ethanol and glycerol, are products of the winemaking process. Although sugars are either partially or completely transformed, sugar import and accumulation into the ripening berry is a major parameter of wine quality. Sugar status is directly related to the final alcoholic content of wine, and regulates several genes responsible for the development of its aromatic and organoleptic properties. Physiological ripeness is reached when the grapes achieve sufficiently high sugar levels without loosing too much acidity; however, aromatic and phenolic compound content must also be taken into account. Softening and water content are other essential characteristics of a ripe berry. From a winemaker point of view, optimal grape maturity is essential for wine quality, but is difficult to assess because it is under multifactorial control, involving grapevine cultivar variety and environmental parameters such as soil, temperature, exposure to sun, and hormonal regulation. Continued study of the key control points in grape ripening is crucial if we ultimately hope to improve grape and wine quality.

https://repositorium.sdum.uminho.pt/bitstream/1822/6820/1/Conde%20et%20al.2007%28review%29.pdf

Biochemical Changes throughout Grape Berry Development and Fruit and Wine Quality

Ethylphenols are important aromatic compounds of red wines. These compounds are formed in wines by some yeast species belonging to the genus Brettanomyces/Dekkera in the presence of hydroxycinnamic acids. These volatile phenols are responsible for the ‘phenolic’, ‘animal’ and ‘stable’ off-odours found in certain red wines. The results presented show that the synthesis of the high quantities of ethylphenols found in the ‘phenolic’ red wines can occur during the ageing of wines having normally completed their alcoholic and malo-lactic fermentations. This olfactory fault caused by Brettanomyces/Dekkera is found more frequently than the classical ‘mousy-taint’ attributed to this yeast genus. In addition, the study of the mechanisms of biosynthesis of ethylphenols by Brettanomyces/Dekkera has shown the sequential activities of two enzymes. The first, is a cinnamate decarboxylase (CD), which assures the transformation of certain cinnamic acids into the correspondent vinylphenols; the second is a vinylphenol reductase, which catalyses the reduction of vinylphenols into ethylphenols. The CD activity of Brettanomyces/Dekkera is not inhibited by the polyphenolic compounds of red wines (procyanidins and catechins) while these compounds do inhibit the CD activity of Saccharomyces cerevisiae. On the other hand, the substrate specificities of the CD activities of Brettanomyces/Dekkera and Saccharomyces are different.

The origin of ethylphenols in wines

Spoilage yeasts in the wine industry.

Sequence-based analysis of the bacterial and fungal compositions of multiple kombucha (tea fungus) samples.

The formation of 4-ethyl and 4-vinyl derivatives of guaiacol, phenol and syringol from ferulic acid,p-coumaric acid and sinapic acid, respectively, byBrettanomyces sp. in a synthetic medium was studied by gas chromatography-mass spectrometry. Some of these metabolites possess strong spicy, smoke-like, medicinal, clove-like, woody or phenolic odours and their role as spoilage compounds in wine is discussed. Their formation appears to be characteristic of this yeast genus and its sporulating formDekkera, suggesting these yeasts are Pof+. This paper attempts to clarify the distinctive and ‘characteristic’ odours which have long been attributed toBrettanomyces yeast metabolism.

Tamila Heresztyn

Papers

Metabolism of volatile phenolic compounds from hydroxycinnamic acids by Brettanomyces yeast