Effect of lees manipulation on the chemical and sensorial characteristics of New Zealand Sauvignon blanc wine : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Sauvignon blanc wine currently comprises about 86% of total NZ wine exports. Its success has been ascribed to its distinctive flavour and aroma, which has been the subject of much research. However, less attention has been paid to the role of palate structure (e.g. mouthfeel) in defining the style, and to the effects of specific winemaking techniques such as lees contact during wine aging. In this study, the effects of different lees management techniques (lees type, stirring frequency, and addition of β-glucanse) on the release of chemical compounds (i.e. nitrogenous compounds, polysaccharides, mannoprotein, β-glucan and glycerol) in model wine were investigated. Because yeast autolysis is a slow process at low temperatures and at the low pH values existing during winemaking, the study also investigated the release of chemical compounds from pulsed electric field (PEF) induced yeast autolysis using rehydrated active yeast with/without addition of β-glucanse. In addition to limited information on lees management appropriate to New Zealand styles of Sauvignon blanc, the lexicon to describe Sauvignon blanc wine mouthfeel is poorly investigated. In this study, napping® was used in order to try and capture terms for the description of mouthfeel in Sauvignon blanc wine, and to determine how these words relate to the chemical composition of wines. Time and lees materials had a significant impact on the concentrations of total protein, primary amino acids nitrogen (PAN), neutral and acidic polysaccharides, mannoprotein, β-glucan and glycerol in model wines (P < 0.001). In addition, inactivated yeast was a good source of amino acids, especially Pro, Arg, Glu and Gln. Inactivated yeasts was a better source of polysaccharides than rehydrated yeasts and collected lees. The majority of the polysaccharide released was in the neutral form and reached concentrations ranging from 600 to 800 mg galactose/L on day 160 in model wine. Both addition of β-glucanases and stirring frequency were minor factors that affected the release of chemical compounds from lees material. Stirring frequency had a significant impact on the concentrations of protein, PAN and neutral polysaccharide (P < 0.05). In addition, stirring frequency showed a statistical impact on protein, PAN and polysaccharide in model wines, but differences were small compared with the overall changes that were achieved at the end of the aging experiment. The study also showed it was feasible to accelerate on-lees aging with pulsed electric field. The experiment demonstrated that the application of PEF (5.5 and 10.0 kV/cm field strength) to lees (5% w/v, rehydrated yeasts) provoked a release of intracellular materials, such as nitrogenous compounds, polysaccharides, and mannoprotein. In addition, time and lees materials also had a significant impact on the concentrations of total protein, primary amino acids nitrogen (PAN), neutral and acidic polysaccharides, mannoprotein, β-glucan and glycerol in model wines (P < 0.001). In the current study, perceived sweetness and acidity seemed to be the major criteria for sorting the commercial examples of Sauvignon blanc wines. In total, 253 descriptors were collected but more than half of these descriptors were used no more than twice on different occasions, and a combination of synonyms was not able to reduce this number significantly. Descriptors that had a frequency of more than 20 were too few to create a comprehensive lexicon. There was no precise correlation between chemical composition and collected descriptors (especially for the ones with low frequency). However, the distribution of wines on the consensus map seemed to be associated with the vinification technique, namely, on-lees aging and vessels used during fermentation and post fermentation. Panellists were able to distinguish the standard and on-lees aged Sauvignon blanc wines.