Author: Honglei Zou
Publisher:
ISBN:
Category : Antioxidants
Languages : en
Pages : 340

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Book Description

Author: Fatma Hatipoglu
Publisher:
ISBN:
Category : Antioxidants
Languages : en
Pages : 194

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Book Description

Author: Tanya Rutan
Publisher:
ISBN:
Category : Pinot noir (Wine)
Languages : en
Pages : 314

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Book Description
The importance of Pinot noir for the New Zealand wine industry has grown and stands second only to Sauvignon blanc in production volume. This thesis investigates the chemical composition of the aroma of Central Otago Pinot noir and its sensory description with the aim of characterising it in a way that an association is made with the typicality of the region. The first stage included a general exploration of the composition of Pinot noir where the chemical aroma, phenolic, tannin composition and colour properties of 105 Pinot noir wines from New Zealand, Australia, France and USA were determined using five different analytical methods across two vintages. The main finding was that the chemical constituents of Pinot Noir wines can vary both between and within different growing regions. There were several compound families where perception thresholds were exceeded for most of the wine samples, including C13 norisoprenoids, higher alcohols, esters of isoacids and fatty acids and cinnamic esters; these can be considered of importance to the overall varietal aromas of Pinot Noir wines. The second aim was to focus on Pinot noir wines from Central Otago where both chemical composition and sensory attributes were explored using reconstitution studies. Aroma Extract Dilution Analysis (AEDA) was applied to two distinct Central Otago Pinot noir wine styles, a blended estate and a single vineyard premium, over two consecutive vintages. The aroma compounds and/or compound families of importance varied across the wines, while a number of compounds were in common. A total of 42 odorants were identified in the AEDA study with flavour dilution (FD) factors ranging from 3 to 19683, with over 20 having FD > 81. The compounds with the highest FDs for the Estate wines were fruity esters and phenylethyl alcohol, while for the Premium wines the norisoprenoids and volatile phenols originating from oak had the highest FDs. The aroma reconstitution experiments, which considered both chemical and sensorial properties, revealed no overwhelming differences when compound families were omitted. Overall, these results suggest that Central Otago Pinot noir wines do not depend on a few key odorants for their aromatic complexity, but instead on the interactions of many aromatic compounds. An additional aim of the study was to measure the effects on wine quality and volatile composition of two cluster thinning regimes on Vitis vinifera cv. Pinot noir in vineyards located in Central Otago across three seasons. The main finding here was that cluster thinning may have an effect on ripening times and the non-volatile and volatile chemical composition of the subsequent wines. These effects may also lead to detectable sensory differences in the final product. It would seem that crop thinning, while a costly practice due to increased labour and yield reduction, is effective in influencing wine quality. However, a particularly intense level of thinning was not necessary to achieve differences in the wines, as a moderate level of thinning also provided a marked enhancement to several attributes.

Author: Diane Youngeun Choo
Publisher:
ISBN:
Category :
Languages : en
Pages : 180

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Author: Ryan Elliott Hodgins
Publisher:
ISBN:
Category :
Languages : en
Pages : 242

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Book Description

Author: Thomas M. Fitzpatrick
Publisher:
ISBN:
Category :
Languages : en
Pages : 732

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Book Description

Author: Zhijing Ye
Publisher:
ISBN:
Category : Antioxidants
Languages : en
Pages : 330

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Book Description

Author: Blair James Rountree
Publisher:
ISBN:
Category : Antioxidants
Languages : en
Pages : 230

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Book Description

Author: Brandt Bastow
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
Hyperoxidation is a pre-fermentative winemaking technique that involves deliberate O2 saturation of a non-sulphited grape must. This alternative winemaking practice is used to combat oxidative browning, decrease phenolic concentrations, reduce necessary antioxidant protection, increase shelf-life and improve mouth feel. Conventional white winemaking practices involve the promotion and preservation of fruity, floral & varietal aromas through the use of antioxidants in a reductive winemaking environment. Aim: Examine the effects of hyperoxidation on aroma and phenolic composition in three New Zealand white wine varietals; Chardonnay, Pinot gris and Sauvignon blanc. This research stems from requests within the wine industry, where hyperoxidation applications are being implemented in order to replace wine fining, modulate phenolics and reduce the browning potential of the final product. Methods: Grape musts were divided into four pre-fermentation groups, consisting of musts that were either treated using hyperoxidation, or left untreated, and in each case with and without antioxidant (SO2) protection; some commercially hyperoxidised Pinot gris and Sauvignon blanc must was also provided. Each treatment group was fermented in triplicate. Phenolics were assessed by HPLC-DAD. Varietal thiols were quantified using GC-MS by means of ethyl propiolate derivatisation. HS-SPME-GC-MS was used to analyse volatile aroma compounds. UV-Vis (A420) was used to quantify brown pigment concentrations. Findings: Hyperoxidation of unprotected musts reduce concentrations of phenolic compounds in white wines, with hydroxycinnamic acids being the most affected. Varietal thiol biogenesis also decreased as a consequence of the pre-fermentation technique. Volatile aromas were either increased (select fatty acids and higher alcohols) or decreased (select fatty acids, higher alcohols, terpenes, C6-compounds and esters) in concentration following hyperoxidation. Contrasting results have appeared between the commercially hyperoxidised wines and the laboratory scale hyperoxidation treatments in terms of volatile aroma concentrations; with esters showing the most conflicting outcomes. The majority of the hyperoxidised musts produced wines with higher concentrations of brown pigments. Conclusions: The results of this experiment have shown substantial evidence of the effects of hyperoxidation on the phenolic and aroma profile in New Zealand white wines. Future studies should investigate this experiment's gaps in evidence, fine tune wine production and analytical analysis and investigate sensory analysis.

Author: Xiaotong Lyu
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
Varietal thiols are crucial aroma compounds present in white wines, and especially contribute to characteristic New Zealand Sauvignon Blanc wines. They provide wines with passion fruit, tropical, stalky and grapefruit aromas. Much research has focused on the formation pathways of these compounds, so as to increase these aromas in Sauvignon Blanc wines. One of the main pathways identified involves conjugated precursors. Recently, an alternative pathway has been proposed, which is through the addition to C6 compounds of a sulfur donor, such as H2S, to form the varietal thiol 3-mercaptohexanol (3MH). Oxygen can be very detrimental to the formation and stability of thiol compounds. Thus, the use of antioxidants is important throughout winemaking practices to protect thiol compounds from oxidation. Elemental sulfur is a common fungicide applied to grapes and leaves in vineyards before harvest. The residues of elemental sulfur have been found to increase the production of H2S, and also varietal thiol compounds. Nevertheless, it also has the potential to generate unwanted reductive sulfur aroma compounds. Micro-oxygenation has been discussed as a way to solve the unpleasant aroma problems caused by elemental sulfur residues. This thesis aims to investigate the effects of different conditions of grape processing or fermentation on the aroma profile of New Zealand white wines. Experiments have been designed to study how alternative antioxidants (glutathione and ascorbic acid) impact on the aroma compounds of Sauvignon Blanc and Pinot Gris wines. Other experiments were undertaken to compare the differences between the aroma compounds in the Sauvignon Blanc, Pinot Gris, and Chardonnay wines with or without antioxidant additions, or with a high level of elemental sulfur addition. Sensory analyses were also performed to compare the Sauvignon Blanc and Pinot Gris wines produced with these treatments. Attention was also paid to the effectiveness of two gas sparging regimes (oxygen and nitrogen), applying during fermentation, on the removal of reductive sulfur aromas in Sauvignon Blanc wines. Additions of glutathione to the grape juices increased the levels of varietal thiols in the finished wines. The lowest levels of varietal thiol compounds were found in the wines with little supplementary antioxidants added. Furthermore, a high level of the joint combination of ascorbic acid and glutathione provided the wines with even higher thiol production. The high level of ascorbic acid addition also protected phenolic compounds from oxidation in the wines. A high level of antioxidants added to the juices at harvest remarkably increased the level of thiol productions, when compared to no supplementary antioxidant addition, in Sauvignon Blanc, Pinot Gris, and Chardonnay wines. Moreover, the varietal thiol levels in the Pinot Gris and Chardonnay wines were just as high as with the Sauvignon Blanc wines, when efficient antioxidant protection was provided. It is also worth noting that the sensory analyses showed the Pinot Gris wines maintained their varietal characteristics, even when high levels of thiols were present. Further increases in the thiol production were observed in the wines with extra elemental sulfur additions. Finally, increasing the amount of elemental sulfur addition to the juice before pressing also led to an increase in the formation of several thiol compounds, including some unwanted reductive compounds, as a consequence of the reduction of elemental sulfur to H2S in the early stages of fermentation. Additions of oxygen added during fermentation were not high enough to effectively remove the undesirable reductive aroma compounds, while a slight decrease was observed in the concentration of the varietal thiols. Likewise, few were observed in the concentrations of unwanted volatile sulfur compounds, or other chemical compounds, with the juices sparged with nitrogen during fermentation.