Composition of volatiles of pinot noir wine as affected by differing levels of DAP supplementation

Abstract

Cental Otago Pinot noir grapes from 2009 vintage were fermented as 18 kg microvinifications, using Saccaromyces cerevisiae var. bayanus yeast EC118. The two treatments employed were nitrogen addition to supplement yeast requirements and aging artificially to assess whether any changes caused by the DAP additions were impacted by long-term storage. The resulting three levels of nitrogen were: Control 450 mg/L YAN, 600 mg/L YAN and 700 mg/L YAN. Half the wines were subjected to a short-term artificial ageing (6 weeks at 30° C) and then aged at 8° C for 8.5 months. The remainder were naturally aged for 10 months at 8° C.

The chemical composition of the treatment wines was investigated. Standard wine composition parameters were determined (e.g. alcohol, titratable acidity, residual sugar). HS-SPME-GC-MS methods were used to measure specific volatile fatty acids, esters and sulphides. A sensory panel of wine professionals was used to determine if there were sensory differences between the wine treatments.

Statistical analysis on the chemical data using MANOVA, principal component analysis, and canonical variate analysis showed the following results: a) esters concentrations tended to decrease with nitrogen addition with the exception of ethyl octanoate, ethyl decanoate, hexyl acetate and ethyl 2 methyl butanoate. Conversely, artificially aging the wines significantly increased the concentration of four esters and decreased hexyl acetate; b) fatty acid concentrations decreased with nitrogen addition with the exception of decanoic acid, which significantly increased. Artificial aging of the wines caused a significant increase in decanoic acid concentration; c) dimethyl sulphide (DMS) decreased across the DAP amendments, however DMS and methanethiol both increased with artificial aging. Multidimensional scaling analysis of the sensory data showed the participants could differentiate that the wines had age related differences. Any sensory effects from variations in DAP addition were not able to be perceived either because the variation was to subtle or overwhelmed by the more obvious differences caused by the artificial aging. The aged wines were described as more “mature”, “reduced”, “jammy” with less “floral, fruity” on the nose. Significant increases in the fatty acid decanoic acid with aging seems to be partially responsible for the maturity characteristics. PLSR results correlated it to the “spicy” characteristics. Ethyl octanoate and 2 methyl ethyl butanoate were related to “maturity” and ethyl decanoate and ethyl isobutyrate to “jammy”.