Influence of fermentation temperature on volatile thiols concentrations in Sauvignon blanc wines

The effect of Saccharomyces cerevisiae strains on the amount of 4-mercapto-4-methylpentan-2-one, a major varietal aroma of Sauvignon blanc wines, was demonstrated by previous research work. However, the influence of different alcoholic fermentation parameters on the levels of volatile thiols (4-mercapto-4-methylpentan-2-one, 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate) in wines has not yet been investigated. The impact of fermentation temperature on the final amount of volatiles thiols and on some other analytical parameters (ethanol, total acidity, residual sugars, volatile acidity) was determined in a model medium and in grape juice. Interaction between fermentation temperature and yeast strain was also tested. The fermentation temperature influenced the amount of volatile thiols irrespective of the yeast strain used. The final levels of 4MMP and 3MH in model medium and in wines were higher when the alcoholic fermentation is conducted at 20 degrees C than at 13 degrees C. The 3MHA, which was correlated with the amount of 3MH determined in wines, was also higher when the alcoholic fermentation was conducted at 20 degrees C. From a technological point of view, the choice of yeast strain and fermentation temperature has a decisive influence on the concentrations of the varietal aromas of Sauvignon blanc wines.     

The influence of yeast on the aroma of Sauvignon Blanc wine

The main objective of this study was to investigate the effect of different Saccharomyces cerevisiae wine yeast strains on the concentration of aroma-enhancing volatile thiols and fermentation metabolites in Sauvignon Blanc wine. Seven commercial wine yeast strains were selected based on their putative ability to modulate the concentrations of the fruity volatile thiols, 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercapto-hexanol (3MH) and 3-mercapto-hexylacetate (3MHA). Each of these yeasts was used to produce Sauvignon Blanc wines under controlled conditions, in triplicate, in 20-L quantities. The levels of 4MMP, 3MH and 3MHA in these wines were quantified using the p-hydroxymercuribenzoate method. In addition, a total of 24 volatile yeast-derived fermentation aroma compounds were also quantified using headspace solid-phase microextraction coupled with gas chromatography mass spectrometry (HS-SPME–GC–MS). Formal sensory analysis was conducted by 12 trained assessors and, additionally, a panel of 24 experienced wine industry professionals assessed the wines and ranked them in order of preference. The results indicated that the yeast strains varied significantly in terms of their capabilities to (i) produce volatile thiols and fermentation metabolites; and (ii) to modulate the varietal characters of Sauvignon Blanc wine. Yeast strains that produced the highest levels of volatile thiols were responsible for wines with the highest perceived intensity of fruitiness, and these wines were preferred by the tasting panels. While the ‘green’ characters in Sauvignon Blanc wines can be manipulated through vineyard management, the ‘tropical fruity’ characters appear to be largely dependent on the wine yeast strain used during fermentation. Therefore, the choice of yeast strain offers great potential to modulate wine aroma profiles to definable styles and predetermined consumer market specifications.     

Contribution of cysteine and glutathione conjugates to the formation of the volatile thiols 3‐mercaptohexan‐1‐ol (3MH) and 3‐mercaptohexyl acetate (3MHA) during fermentation by Saccharomyces cerevisiae

Background and Aims: 3‐Mercaptohexan‐1‐ol (3MH) and its ester 3‐mercaptohexyl acetate (3MHA) are potent aromatic thiols that substantially contribute to varietal wine aroma. During fermentation, non‐volatile 3MH conjugates are converted by yeast to volatile 3MH and 3MHA. Two types of 3MH conjugates have been identified, S‐3‐(hexan‐1‐ol)‐L‐cysteine (Cys‐3MH) and S‐3‐(hexan‐1‐ol)‐glutathione (GSH‐3MH). Yeast‐driven formation of 3MH from these precursors has been previously demonstrated, while the relationship between 3MHA and GSH‐3MH remains to be established. This paper aims to investigate yeast conversion of GSH‐3MH to 3MH and 3MHA, and to assess the relative contribution of each individual conjugate to the 3MH/3MHA pool of finished wines. Methods and Results: Fermentation experiments were carried out in model grape juice containing Cys‐3MH and GSH‐3MH. We found 3MH formation from GSH‐3MH to be significantly less efficient than that of Cys‐3MH. Conversely, esterification of 3MH to 3MHA was higher when 3MH was formed from GSH‐3MH. Additional in vitro assays for measuring enzyme cleavage activity suggest the involvement of a different mechanism in 3MH conversion for the two precursors. Conclusions: These results indicate that although both 3MH conjugates can be converted by yeast, the type of precursor affects the rate of formation of 3MH and 3MHA during fermentation. Significance of the Study: Management of the pool of aromatic thiols during fermentation can depend on relative proportions of different 3MH conjugates.     

The yeast IRC7 gene encodes a β-lyase responsible for production of the varietal thiol 4-mercapto-4-methylpentan-2-one in wine

Three varietal thiols are key aroma compounds in Sauvignon Blanc wines: 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexanol (3MH) and its acetylated derivative 3-mercaptohexyl acetate (3MHA). Screening of Saccharomyces cerevisiae strains identified a clinical isolate with elevated 4MMP production after fermentation. Bulked Segregant Analysis of a cross between this isolate and the laboratory strain revealed a single major locus for 4MMP production near the telomere of chromosome 6. Deletion of the IRC7 gene from this region in YJM450 reduced 4MMP production below detectable levels, but did not affect yields of 3MH, in Sauvignon Blanc wine. Sequencing revealed that the IRC7 gene in YJM450 had been introgressed from a strain of Saccharomyces paradoxus. Most strains of S. cerevisiae, including the laboratory strain S288C, have a 38-bp deletion that inactivates IRC7. Overexpression of a full-length S. cerevisiae allele of IRC7 in a wine yeast, Zymaflore F15, increased 4MMP production in Sauvignon Blanc wine from undetectable levels (<10 ng L⁻¹) to concentrations of 1000 ng L⁻¹, and also increased 3MH and 3MHA. Biochemical analysis of soluble protein extracts showed that both the cerevisiae and paradoxus IRC7 proteins show β-lyase activity, with a substrate preference for cys-4MMP over cys-3MH.     

Volatile aroma and sensory analysis of black raspberry wines fermented by different yeast strains

Robus coreanus Miquel is a small berry fruit used for Korean black raspberry (KBR) wine‐making. Twelve different yeast strains were investigated by laboratory‐scale fermentation to develop a wine with a high flavour quality. Volatile aroma compounds from the wines were analysed using headspace–solid phase microextraction–gas chromatography–mass spectrometry and sensory evaluation was performed to evaluate the flavour characteristics. The volatile aroma compounds that mostly contributed to the flavour of KBR wines were those related to fruity (esters) and floral (terpenes) aromas. Fifteen out of the 67 identified volatile compounds showed higher odour activity values than other compounds in the wines, and these compounds were considered as important contributors to the final aromas of the wine. Additionally, the KBR wine fermented by the M1 yeast strain had the highest sensory preference because of higher fruity and floral aroma characters compared with other wines. In addition to the M1 strain, the other yeast strains that produced favourable sensory characteristics included Enoferm CSM, Uvaferm VRB, Lalvin ICV GRE, Lalvin ICV Opale and LevureSeche Active. Of these strains, the M1 strain produced a particularly excellent black raspberry wine, and thus could be applied for further large‐scale production of black raspberry wines. It is also expected that this work will expedite research on the production of high‐quality black raspberry wines with beneficial physicochemical properties, functionality and good sensory characteristics. Copyright © 2015 The Institute of Brewing & Distilling     

Co-fermentation with Pichia kluyveri increases varietal thiol concentrations in Sauvignon Blanc

Background and Aims:  Volatile varietal thiols are one class of yeast metabolite that add aroma/flavour to Sauvignon Blanc, particularly to the Marlborough style from New Zealand. While various strains of Saccharomyces cerevisiae are known to liberate such thiols, there are no data examining whether non- Saccharomyces species effect concentrations of these thiols in wine.
Methods and Results:  We screened a variety of New Zealand wine yeast isolates and found some that were able to liberate either 3-mercaptohexan-1-ol (3MH) or 3-mercaptohexyl acetate (3MHA). We show that co-fermentation with specific commercial strains and an isolate of Pichia kluyveri from New Zealand, at a 1:9 starting ratio, significantly enhances the 3MHA concentrations in Sauvignon Blanc compared with single species ferments.
Conclusions:  Co-fermentation with this isolate of P. kluyveri may provide a means to elevate 3MHA concentrations in Sauvignon Blanc; the mechanism behind this increase is unknown.
Significance of the Study:  Techniques that allow the predictable manipulation of varietal thiols potentially provide tools for winemakers to alter wine style without the use of genetically modified organisms.     

Yeast and bacterial modulation of wine aroma and flavour

Wine is a highly complex mixture of compounds which largely define its appearance, aroma, flavour and mouth‐feel properties. The compounds responsible for those attributes have been derived in turn from three major sources, viz. grapes, microbes and, when used, wood (most commonly, oak). The grape‐derived compounds provide varietal distinction in addition to giving wine its basic structure. Thus, the floral monoterpenes largely define Muscat‐related wines and the fruity volatile thiols define Sauvignon‐related wines; the grape acids and tannins, together with alcohol, contribute the palate and mouth‐feel properties. Yeast fermentation of sugars not only produces ethanol and carbon dioxide but a range of minor but sensorially important volatile metabolites which gives wine its vinous character. These volatile metabolites, which comprise esters, higher alcohols, carbonyls, volatile fatty acids and sulfur compounds, are derived from sugar and amino acid metabolism. The malolactic fermentation, when needed, not only provides deacidification, but can enhance the flavour profile. The aroma and flavour profile of wine is the result of an almost infinite number of variations in production, whether in the vineyard or the winery. In addition to the obvious, such as the grapes selected, the winemaker employs a variety of techniques and tools to produce wines with specific flavour profiles. One of these tools is the choice of microorganism to conduct fermentation. During alcoholic fermentation, the wine yeast Saccharomyces cerevisiae brings forth the major changes between grape must and wine: modifying aroma, flavour, mouth‐feel, colour and chemical complexity. The wine bacterium Oenococcus oeni adds its contribution to wines that undergo malolactic fermentation. Thus flavour‐active yeasts and bacterial strains can produce desirable sensory results by helping to extract compounds from the solids in grape must, by modifying grape‐derived molecules and by producing flavour‐active metabolites. This article reviews some of the most important flavour compounds found in wine, and their microbiological origin.     

两种酿酒酵母混合发酵对赤霞珠干红葡萄酒香气成分的影响

以酵母F15单独发酵为对照,分别添加不同比例的酵母EC1118和F15（1∶9、3∶7和5∶5）混合发酵酿制赤霞珠干红葡萄酒,测定其 基本理化指标,采用搅拌棒吸附萃取（SBSE）和气相色谱-质谱联用（GC-MS）技术提取检测葡萄酒中的香气成分,并进行主成分分析 （PCA）。 结果表明,酵母EC1118和F15混合发酵酿制的葡萄酒的理化指标均符合国家标准GB/T 15037—2006《葡萄酒》,香气成分中 的酯类、醇类和酸类等物质的含量均有所增加。与酵母F15单独发酵相比,酵母EC1118和F15（3∶7）混合发酵可以显著提高赤霞珠干红 葡萄酒的酒精度,增加香气成分（P＜0.05）,增强葡萄酒的果香和花香。     

Thiol precursors in Catarratto Bianco Comune and Grillo grapes and effect of clarification conditions on the release of varietal thiols in wine

Background and Aims

Varietal thiols characterise the typical aroma of several white wines, such as Sauvignon Blanc. Their presence and sensory perception were suggested in two Sicilian grape cultivars, Catarratto Bianco Comune (CBC) and Grillo, though it has not been analytically proven.

Methods and Results

Varietal thiol precursors and free varietal thiols were assessed in CBC and Grillo grapes, musts and wines by ultra‐performance liquid chromatography/electrospray ionisation high‐resolution MS. The isobaric compounds including S‐3‐(hexanal)‐glutathione and S‐3‐(4‐mercapto‐4‐methylpentan‐2‐one)‐glutathione (GSH‐4MMP) were distinguished by comparing their accurate masses and high‐resolution‐MS/MS spectra with those of their synthetic standards. S‐3‐(Hexanal)‐glutathione, S‐3‐(hexan‐1‐ol)‐glutathione and S‐3‐(hexan‐1‐ol)‐cysteine were found in grape, must and wine, whereas GSH‐4MMP and its hydrolysed forms were not found. Their concentration decreased during winemaking, mostly after grape pressing. We compared the effect of clarification conditions based on the exposure of must to either air or CO₂ on the concentration of thiol precursors and free thiols in wine; however, negligible differences were observed. The concentration of free thiols in the wines was found to be in the range 400–1100 ng/L and they were unaffected by the two clarification conditions tested.

Conclusions

The isobaric S‐3‐(hexanal)‐glutathione and GSH‐4MMP were clearly distinguished for the first time by ultra‐performance liquid chromatography/high‐resolution MS through their retention times and MS spectra. These varietal thiols were revealed in CBC and Grillo wines for the first time. The air‐free and air‐exposed clarification treatments had little effect on the concentration of the varietal thiols.

Significance of the Study

This study highlights the major impact of the varietal thiols (mainly 3‐mercapto‐hexan‐1‐ol and its acetate form) on the sensory properties of CBC and Grillo wines.     

葡萄酒香气来源和形成研究进展

香气是衡量葡萄酒质量的一个重要部分。以葡萄酒香气的3大来源-品种香、发酵香、陈酿香为主线,对葡萄酒中活跃香气成份的形成进行概述。包括葡萄果实中的香气物质和葡萄利用酵母在酒精发酵时期产生的香气物质。同时,对苹果酸-乳酸发酵、葡萄酒的老化、成熟与葡萄酒香气的关联也进行了讨论,以期促进葡萄酒香气的进一步研究。     

美极梅奇酵母的代谢特性及其在葡萄酒生产中的应用前景

美极梅奇酵母是一种在成熟葡萄浆果表面和葡萄酒发酵初级阶段普遍存在的非酵母属酵母。该文从该酵母与葡萄酒相关环境的适应性、产酶特性、抗菌特性,及其对酒精发酵、葡萄酒成分、风味品质与色泽稳定性等方面的影响进行了论述,以期为美极梅奇酵母在葡萄酒生产中的合理应用提供参考。美极梅奇酵母在降低葡萄酒酒精含量、增加甘油含量、增强品种香气、提高感官品质、促进红葡萄酒色泽稳定等方面具有良好的潜质,但这些特性也存在着较大的菌株差异性。     

Effect of micro-oxygenation on the evolution of aromatic compounds in wines: Malolactic fermentation and ageing in wood

The effect of micro-oxygenation on the aromas of two varietal wines (Tempranillo and Cabernet Sauvignon) when alcoholic fermentation is complete was examined. Several factors, such as whether malolactic fermentation (MLF) took place in barrels or stainless steel vats and ageing time in oak barrels, were taken into account. Major aroma components were studied using GC-FID and minor compounds were studied by GC-MS analysis before and after MLF and after 4 and 8 months of maturation in oak barrels. Sensorial analysis was performed to describe and quantify the different wine notes. Micro-oxygenation affects different compounds but the effect depends to a great extent on the grape varietal used; the effect of micro-oxygenation was more marked on the aroma of Cabernet Sauvignon wine than Tempranillo wines. The concentration of extractable compounds of wood was higher in wines after MLF in barrels than in wines after MLF in steel vats; wines with steel vat MLF had fewer toast and wood notes. The compounds that showed significant differences in concentration after 8 months of maturation were present in higher concentrations in wines fermented in barrels than in stainless steel vats. Barrel-fermented wines were sweeter, with wood and toast notes, fewer alcohol notes and fewer reductive notes.     

啤酒酵母酿造葡萄酒及香气成分GC-MS分析研究

以宁夏贺兰山东麓产区酿酒葡萄为原料酿造葡萄酒,测定其感官指标、理化指标,并通过顶空固相微萃取-气质联用（HS- SPME-GC-MS）技术分析啤酒酵母单独发酵（SY）、葡萄酒酵母单独发酵（AY）及二者混菌（1∶1）发酵（MY）酿造葡萄酒的香气物质,并计算气味活力值（OAV）。结果表明,3个样品的感官评分顺序依次为MY＞SY＞AY,理化指标符合相关国标;MY、SY、AY样品GC-MS分析分别共检测出22种、20种、15种香气成分,其中含量最高的均为异戊醇,MY、SY样品中的酯类成分较AY样品种类多;OAV分析结果进一步显示,对3个样品香气贡献最大的物质均为酯类,MY样品OAV＞1的香气成分为4种。啤酒酵母酿造的葡萄酒风味独特,并且混菌发酵可以提升葡萄酒品质。     

沙棘原汁澄清处理对沙棘酒香气成分的影响

为研究沙棘原汁澄清处理对沙棘酒发酵速度和香气成分形成的影响,利用果胶酶对沙棘原汁进行澄清处理。分别对沙棘澄清汁和未处理的沙棘原汁调整到糖度23%、pH3.7,然后接入0.18%的活性干酵母于28.5℃下发酵,陈酿后采用气-质联用仪(GC-MS)对各发酵酒进行香气成分检测。结果表明:以澄清汁为原料发酵的沙棘酒中检测出58种香气化合物;原汁发酵的沙棘酒中检测出52种香气成分,其中有28种非两者共有,产生了非常明显的香气差异。主要香气成分为3-甲基-1-丁醇和辛酸乙酯,用澄清汁发酵的沙棘酒其相对含量分别为31.24%和10.40%,较原汁发酵的沙棘酒分别提高了16.45%和5.32%。因此表明对沙棘汁澄清处理更有利于沙棘酒香气的形成。     

混合果汁起泡酒酿造工艺的研究

以苹果汁、葡萄汁、哈密瓜汁作为原料,对酿造复合型起泡酒的工艺进行研究。采用正规的“留糖法”进行发酵生产,酒中的CO2、酒精、酸糖皆来自于果汁。通过单因素及正交试验确定了葡萄苹果起泡酒最佳工艺条件为德国酵母3#,接种量0.8 g/L,葡萄汁与苹果汁质量比3∶2,发酵醪糖度16%,采用罐内发酵方式对起泡酒进行充气,CO2含量0.15 MPa。哈密瓜苹果起泡酒最佳工艺条件为德国酵母3#,接种量0.8 g/L,哈密瓜汁与苹果汁质量比1∶1,发酵醪糖度14%,采用罐内发酵方式对起泡酒进行充气,CO2含量0.13 MPa。由此最佳工艺条件得到的葡萄苹果起泡酒和哈密瓜苹果起泡酒,酒香和果香协调浓郁,口感酸甜均衡,酒体丰满,杀口力强,后味爽。     

葡萄酒中甘油的生成及其影响因素

甘油具有甜味和粘稠性,是干、半干葡萄酒的主要组成分,对酒的质量具有重要影响。甘油是葡萄酒酵母的正常发酵副产物,主要在葡萄汁发酵初期产生。葡萄酒酵母启动甘油生产原因可能是发酵最初缺少醇脱氢酶,造成氧化还原当量不平衡,细胞生产甘油、消耗NADH以平衡胞内氧化还原电势;葡萄汁中初始糖浓度高造成高渗透压,胞内产甘油作为溶质以抵消高渗透压。不同的酵母之间产甘油能力差别很大。提高甘油量是改进干、半干葡萄酒质量的重要措施之一。筛选高产甘油的葡萄酒酵母、混合菌种发酵、调整葡萄汁成分、改变发酵条件、施加热刺激等均能在不同程度上增加甘油的产量。     

酿酒酵母F15和CC17共接种发酵对赤霞珠葡萄酒品质及感官特性的影响

为解决使用单一商业酵母菌株发酵引起的葡萄酒“同质化”问题,本研究以河北昌黎产赤霞珠葡萄为原料,以商业酿酒酵母（Saccharomyces cerevisiae）F15和本土优良酿酒酵母CC17为发酵剂进行单菌株和双菌株共接种（F15:CC17=1:1）发酵,同时监测酒精发酵过程中比重、温度、残糖、乙醇、总酸、pH、花青素、单宁、总酚、色度和色调的变化。发酵结束（192 h）后,分别对酒的香气成分和感官特性进行了测评。结果表明:与F15单菌株发酵相比,双菌株共接种发酵能够提高赤霞珠葡萄酒中花青素、单宁和总酚含量,增加酒的色度并使色调更趋向于红色;与CC17单发酵相比,共发酵组残糖、总酸含量较低;共发酵调谐主要香气成分,并增加饱和脂肪酸乙酯的含量。此外,感官评价结果表明共发酵葡萄酒色、香、味均优于F15单独发酵。因此,在酒精发酵过程中采用商业酵母与本土菌株共发酵是改善葡萄酒品质和感官特性有效方法。     

天然酵母菌株在葡萄酒酿造中的应用研究

以河北产赤霞珠葡萄为原料,用本土天然酿酒酵母菌株Y14和商业酵母菌株F15酿造干红葡萄酒,并采用固相微萃取结合气质色谱的方法对葡萄酒中的挥发性香气物质进行检测。结果表明,本土酵母菌株在发酵能力方面与商业酵母无明显差别,但在不同酵母发酵葡萄酒中的香气成分种类和含量方面具有较大差别,本土酵母菌株Y14在香气成分生成能力方面具有优势。因此,此菌株具有生产本地特色葡萄酒的潜质。