INFLUENCE OF VINEYARD NITROGEN-FERTILIZATION ON THE CONCENTRATIONS OF MONOTERPENES, HIGHER ALCOHOLS, AND ESTERS IN AGED RIESLING WINES

Riesling wines produced in 1986 and 1988 from vines fertilized with 0, 56, 112, or 224 kg N/ha/year were analyzed in 1991 for free and bound monoterpenes, higher alcohols, and esters. Solid phase extraction using Amberlite(R) XAD-2 resin was employed in the isolation of volatile compounds identified by gas-liquid chromatography/mass spectrometry. Relative recoveries of all compounds ranged from 79% to 112% with coefficients of variation generally less than 7%. Vineyard N fertilization affected the concentration of some free or bound monoterpenes in the aged wines, depending on the monoterpene and vintage. Concentrations of amyl alcohols and 2-phenylethanol decreased with increasing N fertilization while isobutanol and cis-3-hexen-1-ol showed no differences. Concentrations of 1 -butanol, trans-3-hexen- 1 -ol, benzyl alcohol, and the majority of esters increased (p < 0.05) with increased N fertilization. Sensory analysis using triangle difference tests indicated that wines made from grapes fertilized with 0 or 224 kg N/ha significantly differed (p less-than-or-equal-to 0. 01).