WINETECH Technical Yearbook 2021

Volatile thiols and C 13 -norisoprenoids Both 3MH and 3MHA increase with exposure to sunlight, with only the former compound also increasing with UV-B. A study also showed that TDN levels increased in Riesling wine made from sun-exposed grapes. The influence of temperature remains an important factor. Yet another study demonstrated that sun exposure of grapes increased TDN levels in young wines, but after 22 months of ageing, this effect disappeared. Dried fruit aromas A study showed that furaneol, homo­ furaneol and γ-nonalactone increased post- harvest due to light exposure, while MND and (Z)-1,5-octadien-3-one did not. Other aroma compounds There is an association between high UV-B levels and an increase in AAP (2-aminoacetophenon – paint-like, moth­ ball and medicinal aromas) in white wine. High radiation decreases antioxidants such as glutathione and ascorbate (these are “aroma protectants”) in plants, while total phenolics increase with light exposure of grapes. VINE NITROGEN STATUS Green and peppery flavours While numerous studies have shown an

at low concentrations, truffle at medium concentrations, and asparagus at high concentrations) have been found in Bordeaux wines from the very warm 2003 vintage. Aromatic heterocycles also seem to be higher in aged wines from warm vintages. Glutathione, a non-aromatic preserving agent for white and rosé wine aromas, tends to decrease in plants under high temperatures. RADIATION Green and peppery flavours Lower levels of IBMP have been observed in grapes under high radiation. It was shown that the decreasing effect on IBMP levels in grapes happens before véraison. C6 compounds are lower in sun-exposed bunches compared to shaded bunches, while there seems to be a stimulating effect of light on (-)-rotundone. The latter compound can be enhanced by defoliation in cool-climate vineyards. Other monoterpenes Exposure to full sunlight was shown to increase terpenol content in Traminette, whi le exposure to l ight increased monoterpenes in Riesling grape berries. Increases in total substituted esters and linalool were also seen, but the effect of temperature interference remains an important consideration.

fermentation, and hydroxycarboxylic acid ethyl esters produced during malolactic fermentation. Other aroma compounds There is likely a positive link between a higher wine DMS content and increased vine N status, seeing that the formation of pDMS (DMS potential) in berries is related to the abundance of amino acids. Low levels of vine N is associated with higher AAP levels in white wine. VINE WATER STATUS Green and peppery flavours A water deficit has been shown to decrease IBMP content in wine, with no effect seen on C6 compounds. Vines irrigated just prior to véraison had higher (-)-rotundone levels. Volatile thiols and C 13 -norisoprenoids A mild water deficit increases volatile thiols and a severe water deficit decreases volatile thiols. It was observed that vines under a strong water deficit resulted in wine with lower TDN levels. Tabanon (imparts tobacco and spicy aromas) levels in ageing wine showed an increase with water deficit and a remarkable increase in severely water-stressed vines. Wine produced by microvinification from vines under water stress were shown to have high levels of C 13 -norisoprenoids.

increase in IBMP in wine produced from vines with high nitrogen status, there is no direct affect. The increased vigour in vines with higher N offer more bunch shading, which leads to lower grape temperature and exposure to sunlight. The effect of N status on (-)-rotundone is expected to be the same as above. Other monoterpenes It is reported that terpenes decrease with nitrogen fertilisation. Volatile thiols and C 13 -norisoprenoids Many studies have shown an increase in volatile thiols in vines that are naturally high in nitrogen or due to fertilisation. It was also shown that in Pinot noir low nitrogen status resulted in wine with low β-damascenone content. In Riesling, TDN was shown to decrease with high nitrogen fertilisation. Substituted esters and qualitative fruit aromas A study on Tempranillo showed that foliar N fertilisation increased the levels of ethyl hexanoate and ethyl octanoate, while decreasing the level of isoamyl acetate. Another study showed that higher yeast available N increased concentrations of short- and substituted alkyl fatty acid ethyl esters produced during alcoholic

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