- Wine volatile composition is one of the most important constitutes of wine quality, and it is greatly influenced by number of factors. The studies herein were conducted to evaluate the grape and wine aroma affected by different vine nutrient status, vigor and crop levels of Oregon Pinot noir.
In the first study, aroma potentials in early and late maturity Pinot noir grapes were investigated in two consecutive vintages. The grape samples were hydrolyzed under acidic conditions and the released odorants were studied by aroma extract dilution analysis (AEDA). Forty-nine main odor-active compounds were detected in the AEDA. The odorants released with high flavor dilution values were 1-hexanal, β-damascenone, guaiacol and vanillin, together with C₆ aldehydes and alcohols, 4-vinylguaiacol, 4-vinylphenol and 1-octen-3-one. The concentrations of aroma-active compounds were further quantitated by SPME-GC-MS and SBSE-GC-MS. Comparing with early harvest grapes, late harvest grapes released more β-damascenone, vanillin, 4-vinylguaiacol and 4-vinylphenol in both years according to both AEDA and quantitation results, suggesting they were important aroma compounds that contribute to the characteristic of mature Pinot noir grapes.
The second study evaluated the volatile composition of grape berries subjected to varying levels of nitrogen (N), phosphorous (P) and potassium (K) supply. Pinot noir grapevines were grown in a pot-in-pot system for three years (beginning when they were 4-years-old) and fertigated with either complete nutrition (Control) or with reduced levels of either N, P, or K supply while holding all other nutrients constant. Nitrogen was varied from 7.50 mM total N supply (Control) to 1.13 mM in five discreet treatments, while P and K supply were each varied in four discreet treatments with the lowest rate of 0 mM during fertigation events. Aroma volatiles in berries were determined in each year using SPME-GC-MS technique. Results showed that reducing N supply resulted in lower concentrations of C₆ compounds and total β-damascenone in berries across all three years. Low N supply had little impact on monoterpenes. Reducing N supply resulted in higher bound form α-terpineol in two of the three years. Compared to P and K, N supply showed a more profound influence on the volatile profiles of the grape berries, indicating the important role of N in the biosynthesis of berry volatile and volatile precursors. The volatile composition of resulting wines from the same study was also investigated. Results showed that reducing N supply increased the total phenolic content in wine across all years. N supply has a profound impact on wine volatiles with the greatest effect on yeast-derived esters and higher alcohols. In general, reducing N supply decreased straight-chain esters and many straight chain alcohols, but increased the branched-chain esters, and phenethyl ester and phenethyl alcohol in wine across all years. The effect of N supply on monoterpenes in wine was not consistent from year to year. Low N wines also had reduced levels of volatile sulfur compounds in 2 of 3 years. Compared to the Control, reducing N and K supply resulted in lower quantities of total β-damascenone across all years. Altering P supply did not have reproducible effects on wine volatiles from year to year.
The third study investigated the composition of Pinot noir wines produced from vines with varying vegetative vigor levels and two crop levels over three vintages (2011, 2012, and 2013) in the cool climate viticulture region of western Oregon. Wine was produced from grapes grown with two inter-row floor management treatments (tilled or grass) and two crop levels, including full crop and half crop achieved through cluster thinning. Crop
thinning treatments didn’t alter the wine volatile composition. Certain wine volatiles were affected by the vineyard floor management treatments. Wines produced from grapes grown in the Grass treatment (lower vigor) had higher levels of grape-derived compounds such as α-terpineol, β-citronellol, vitispirane and TDN compared to wines produced from the Tilled treatment. Wines from Grass treatment also had higher isoamyl alcohol, phenethyl alcohol, isoamyl acetate, ethyl isobutyrate, ethyl isovalerate, and phenethyl acetate but lower levels of linalool, 1-propanol and 1-octanol. A subproject of this study investigated the carotenoid breakdown and C₁₃-norisoprenoids synthesis in Pinot noir grapes from vines of differing vigor and crop levels (yield). Carotenoid degradation and C₁₃-norisoprenoid synthesis during berry development with different vine balance was monitored from véraison to harvest in year 2013. Our data suggests that vineyard floor management had a greater influence than did cluster thinning on carotenoids composition in grapes. Grape berries from Tilled treatment vines have higher carotenoids and C₁₃-norisoprenoids than the grapes from Grass treatment vines. Multivariance analyses also showed some interactions between the vineyard floor treatments and cluster thinning treatments on the composition of carotenoids and C₁₃-norisoprenoids.