YEAST AND ITS EFFECT ON THE FLAVOUR OF ALCOHOLIC BEVERAGES*

Sensory examination of an aroma model consisting of alcohols, fatty acids, esters and aldehydes, in concentrations estimated in whisky, has proved that—in addition to vicinal diketones—esters predominate as components influencing the aroma, but also some fatty acids exercise a most marked influence. Furthermore, some people possess a good ability to smell certain compounds whereas others cannot smell them as well, but detect other compounds more easily. Within the group of more than 100 identified aroma components, mainly the same substances appear in the volatile aroma fraction of beer, wine and distilled beverages. In view of this, it seems evident that the raw materials utilized for the production of the beverages contribute to no more than a limited extent towards the aroma composition. The aroma components which are most noticeable are produced by the yeast during fermentation, and the nature of the final aroma first and foremost depends upon the kind of yeast used, and upon the fermentation conditions. Although the yeast for the most part produces the same aroma components also In different beverages, considerable variation may occur in the quantities of aroma components even in beverages of the same type. The structure and function of the plasma membrane selectively regulate the uptake of different compounds from the medium into the yeast cell, and the release of the metabolites from the cell into the medium. In this sense, the lipid composition of the plasma membrane and its lipolytic enzymes may possess a decisive importance. The activity of the lipolytic enzymes present in the plasma membrane must be controlled by some regulatory mechanism. If this is the case, the permeability of the plasma membrane can be modified, e.g., by activation of the phospholipases, with consequent degradation of membrane phospholipids. Consequently, it is likely that one of the functions of the lipolytic enzymes present in the plasma membrane is that of participation in the transport processes by changing the permeability properties of the plasma membrane.     

Mead production: effect of nitrogen supplementation on growth,fermentation profile and aroma formation by yeasts in mead fermentation

Mead is an alcoholic beverage, produced since ancient times, resulting from an alcoholic fermentation of diluted honey by yeasts. When it is produced in a traditional manner, mead producers can encounter several problems related to a lack of essential nutrients, such as available nitrogen. Thus, the aim of this study was to evaluate the effect of nitrogen addition to honey‐must on the fermentation performance of two Saccharomyces cerevisiae wine yeasts, QA23 and ICV D47, as well as on the mead composition and production of volatile aroma compounds. A portion of honey‐must was supplemented with diammonium phosphate (DAP) to achieve the nitrogen concentration required by yeast to complete alcoholic fermentation. The supplementation with DAP reduced the fermentation length to around 7 days, but not all sugars were fully consumed, suggesting that other factors could be interfering with yeast growth. For both yeasts the specific growth rate and final biomass were higher in musts supplemented with DAP. Mead final composition was similar under the two experimental conditions. Analysis of the volatile profile revealed that the concentrations of the volatile fatty acids and volatile phenols were higher in meads supplemented with DAP. The concentrations of ethyl hexanoate, ethyl octanoate and isoamyl acetate were above their perception threshold and were higher in meads supplemented with DAP, which could contribute to the enhancement of the fruity character. This study could be useful for the optimization of mead production and quality improvement. Copyright © 2015 The Institute of Brewing & Distilling     

THE INFLUENCE OF LIPIDS DERIVED FROM MALT SPENT GRAINS ON YEAST METABOLISM AND FERMENTATION

The addition to wort of lipids derived from malt spent grains had a pronounced effect on yeast metabolism. The lipids allowed the fermentation of de-oxygenated wort and also stimulated yeast growth and the corresponding rate and extent of fermentation of air-saturated wort by yeast strains having a high oxygen requirement. The lipids increased the fusel alcohols content of beer and decreased the content of esters and medium chain-length fatty acids. The yeast incorporated sitosterol and unsaturated fatty acids from the spent grain lipids and the unsaturated fatty acids changed the pattern of fatty acids and sterols synthesized by the yeast. The fatty acids were present in the spent grain lipids mainly as triglycerides, free fatty acids and phospholipids. Using pure lipid compounds it was shown that the triglycerides were inactive and that the spent grain lipids exerted their effect on fermentation through the synergistic action of free unsaturated fatty acids, sitosterol and phospholipid. Phospholipid could be replaced by the detergent, Triton X-100. The effect of the lipids on the synthesis of esters, fusel alcohols and medium chain fatty acids could be explained solely by their content of unsaturated fatty acids.     

Changes in volatile aroma compounds of traditional Chinese-type soy sauce during moromi fermentation and heat treatment

Considering the important influence of longtime (150 day) moromi fermentation and heat treatment on the aroma formation of traditional Chinese-type soy sauce (TCSS), volatile compounds in samples taken from different stages of moromi fermentation and heat treatment were analyzed by solid phase microextraction coupled with gas chromatography-mass spectrometry. Results showed that a total of 76 volatile compounds were identified in all the samples, and most of the volatile compounds were common. During 150 day of moromi fermentation, relative contents of acids, alcohols, aldehydes and ketones, esters, and furan(one)s along with all the sensory attributes of acidic, alcoholic, fruity, caramel-like, smoky, and malty changed greatly. Notably, relative contents of alcohols, aldehydes and ketones along with the sensory intensities of alcoholic, caramel-like, and smoky of heated sample (80°C/60 min) decreased markedly, whereas there were slight increases in relative contents of furan(one)s, phenols, and sulfur-containing compounds of it. Long-time moromi fermentation and heat treatment have significant influence on the formation and relative contents of volatile compounds in TCSS, whereas changes in volatile compounds and their relative contents of the samples were responsible for the differences in sensory attributes.     

Nitrogen addition influences formation of aroma compounds,volatile acidity and ethanol in nitrogen deficient media fermented by Saccharomyces cerevisiae wine strains

The effects of nitrogen addition into nitrogen deficient/depleted media on the release of aroma compounds post-fermentation were investigated in three commercial yeast strains of Saccharomyces cerevisiae which highlight the yeast strain effect as well as nitrogen effects. By comparing the two timings of nitrogen addition, prior to fermentation or later at stationary phase (72 h), it was shown that nitrogen addition at stationary phase significantly decreases ethanol and acetic acid formation and significantly increases the following compounds: 2-phenylethanol, ethyl isobutyrate, 2-phenylethyl acetate, ethyl 2-methylbutyrate and ethyl propionate in the three strains, and also isovaleric acid, isoamyl alcohol and ethyl isovalerate in both PYCC4072 and UCD522. The strain EC1118 produced significantly less medium chain fatty acids, hexanoic, octanoic and decanoic acids and their respective esters after nitrogen addition. Therefore, timing of nitrogen addition to a ferment media can vary the concentration of certain aroma compound and might provide a means for varying wine composition.     

THE BIOCHEMISTRY OF MATURATION

Negative and positive aspects of maturation are respectively related to aroma and taste modifications. Vicinal diketones, hydrogen sulphide, acetyldehyde being primarily responsible for ‘green’ beer flavours an important feature of maturation is the adjustment of their concentration during the lagering period. The role of secondary fermentation in the removal of these undesirable by-products and the importance of sulphury compounds in determining the typical character of lager beer are reviewed. Particular emphasis is placed upon new enzymatic and genetic approaches to overcome vicinal diketone problems in accelerated fermentation systems using free and immobilized cells. The presence in beer of amino acids, peptides, nucleotides and organic as well as inorganic phosphates is, in part, due to the secretion of these materials by the yeast during lagering. Most of these compounds are contained in internal pools and their actual participation in flavour maturation depends upon intracellular breakdown and accumulation, changes in cell permeability and subsequent exchange possibilities between the yeast cell and the surrounding beer. Participation and practical implications of medium chain length fatty acids in the development of autolytic and yeasty flavours are discussed.     

酱油酿造过程中风味物质的形成与鉴定

为研究酿造工艺对酱油风味形成的影响,运用顶空固相微萃取(HS-SPME)耦联气质(GC-MS)方法测定了黑龙江地区某品牌酱油在发酵过程中挥发性香气成分的组成和变化。研究发现,发酵过程中共检测出了31种香气组分,其中醇类3种,醛类4种,酸类4种,酯类6种,酚类4种,呋喃3种,其他化合物7种;进一步通过测定其香气活性值确定了4种主要的呈香物质:1-辛烯-3-醇、苯乙醛、乙酸、4-乙烯基愈创木酚;主成分分析结果表明:发酵时间为5~42 d时,以1-辛烯-3-醇,乙酸及4-乙烯基愈创木酚为特征组分,而发酵时间为42~59 d时,以苯乙醛为主要组分。     

基于GC-MS法的椰子水及其饮料的风味成分分析

为了对不同成熟度椰子(椰青、嫩椰子、成熟椰子)的椰汁及椰子水饮料中挥发性风味物质组分和含量进行分析,采用蒸馏萃取装置提取样品中的挥发性成分,并用气相色谱-质谱(GC-MS)联用分析技术进行分离鉴定。结果表明,共检测出67种香气成分,分为7大类化合物,包括酯类32种,有机酸11种,醇类7种,醛类3种,酮类3种,酚类4种,其他类7种。在检出的香气物质中,确定主体风味组分主要是醇类、酯类和酸类3类物质,相同的挥发性成分是2,3-丁二醇。不同样品中,这些微量香气成分的种类含量有较大差别,成熟椰子原汁中风味物质的种类和含量较多。因此,椰子水原汁的挥发性成分直接影响椰子水饮料的感官质量。本试验研究为椰子水及其饮料感官品质的深入研究提供了一定的理论依据。     

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.     

HS-SPME-GC-MS法分析发酵过程中荞麦和小麦面团香气成分变化

采用顶空固相微萃取技术和气相色谱-质谱联用技术对比分析荞麦和小麦在不同发酵剂作用下发酵过程中产生香气成分的差异。并基于保留指数和质谱鉴定对挥发性化合物进行鉴定。研究发现未发酵荞麦面团检出38?种香气成分,在酵母和乳酸菌发酵过程中共分别检测出80?种和63?种香气成分;未发酵小麦面团检出11?种香气成分,在酵母和乳酸菌发酵过程中共分别产生42?种和17?种。发酵过程中,荞麦和小麦面团香气种类增加,其中荞麦面团呈现更多香气成分。烃类和酯类是荞麦面团酵母发酵前后主要香气成分,烃类主要为单萜烯和倍半萜烯类,酯类是荞麦面团经乳酸菌发酵前后主要香气成分。小麦经过酵母发酵产生香气成分包括烃类、酯类、醇类、酸类、醛类及醚类,经过乳酸菌发酵产生香气成分种类相对较少,有烃类、酯类、酮类及醛类。荞麦发酵后产生更多活性香气成分。酵母和乳酸菌发酵荞麦和小麦后,香气成分有明显差异。在发酵过程中,香气成分随着发酵时间延长而发生转化。     

关于控制啤酒风味稳定性的技术思考

啤酒是由麦汁经啤酒酵母发酵后产生的一类风味独特的含酒精饮料,其独特风味主爰由酵母在麦汁中的总体代谢产物所产生并决定的,啤酒中主要风味物质包括醇类、酯类,羰基化合物、有机酸、硫化物胺及酚类等,并对其物质来源、影响因素及控制措施加以研究与探讨。     

THE AROMA COMPONENTS PRODUCED BY YEAST IN NITROGEN-FREE SUGAR SOLUTION

In nitrogen-free sugar fermentation yeast produces several other volatile compounds in addition to ethanol. Most of these compounds are distilled over with the ethanol. When the aroma components obtained from the ethanol fraction of a nitrogen-free sugar fermentation were compared with the aroma components of whisky, they showed a qualitatively striking similarity. There was a clear difference in the proportions of the components, however, a fact for which the distillation procedure might be at least partly responsible. The distillate obtained from the fermented sugar solution contained iso-amyl alcohol and β-phenethyl alcohol as well as the ethyl esters of caproic, caprylic, capric, lauric and palmitic acids in considerable amounts. The same acids also appeared as main components among the free acids and, further, isobutyric and isovaleric acid were found quite abundantly. The similarity between the aroma compounds formed in nitrogen-free sugar fermentation and the aroma fraction of alcoholic beverages indicates that the yeast is responsible for the bulk of the aroma compounds produced.     

Yeast autolysis in sparkling wine – a review

Sparkling wine produced by the traditional méthode champenoise requires a second in-bottle alcoholic fermentation of a base wine, leading to the sparkling wine. This second fermentation is followed by prolonged ageing in contact with yeast cells (lees). The autolysis of yeast occurs during the ageing of sparkling wines. During this process, the yeast releases different compounds that modify the organoleptic properties of the wine. The ageing period is required to give these wines their roundness and characteristic aroma and flavour. Autolysis products also influence the foaming properties of sparkling wine. Yeast autolysis is characterised by the hydrolysis of intracellular biopolymers by yeast enzymes activated after cell death. This results in the release of low molecular weight products. This article reviews the recent advances in understanding the yeast autolysis mechanism, the factors affecting autolysis, the nature of the released compounds and their effects on sparkling wine quality.     

Production of sensory compounds by means of the yeast Dekkera bruxellensis in different nitrogen sources with the prospect of producing cachaça

The distilled spirit made from sugar cane juice, also known as cachaça, is a traditional Brazilian beverage that in recent years has increased its market share among international distilled beverages. Several volatile compounds produced by yeast cells during the fermentation process are responsible for the unique taste and aroma of this drink. The yeast Dekkera bruxellensis has acquired increasing importance in the fermented beverage production, as the different metabolites produced by this yeast may be either beneficial or harmful to the end‐product. Since D. bruxellensis is often found in the fermentation processes carried out in ethanol fuel distillation in Brazil, we employed this yeast to analyse the physiological profile and production of aromatic compounds and to examine whether it is feasible to regard it as a cachaça‐producing microorganism. The assays were performed on a small scale and simulated the conditions for the production of handmade cachaça. The results showed that the presence of aromatic and branched‐chain amino acids in the medium has a strong influence on the metabolism and production of flavours by D. bruxellensis. The assimilation of these alternative nitrogen sources led to different fermentation yields and the production of flavouring compounds. The influence of the nitrogen source on the metabolism of fusel alcohols and esters in D. bruxellensis highlights the need for further studies of the nitrogen requirements to obtain the desired level of sensory compounds in the fermentation. Our results suggest that D. bruxellensis has the potential to play a role in the production of cachaça. Copyright © 2014 John Wiley & Sons, Ltd.     

Concentration of volatile compounds in Chardonnay wine fermented in stainless steel tanks and oak barrels

The influence of the type of container used in alcoholic fermentation on the formation of volatile compounds in wine from Chardonnay variety was studied. To do so, must from Chardonnay variety was fermented in both stainless steel tanks and in new Nevers oak barrels. The results obtained showed that wine fermented in barrels had a greater concentration of higher alcohols and esters than wine fermented in tanks. Concentration of isoamyl acetate, ethyl hexanoate, ethyl octanoate and ethyl decanoate was four times higher in wine fermented in oak barrels than in wine fermented in stainless steel tanks. With regard to the concentration of acids, a greater concentration of medium-chain fatty acids (C6:0–C10:0) was noticeable in wine fermented in oak barrels. Given that these acids are toxic for the yeasts, they may be responsible for the slower fermentation rate of wine fermented in oak barrels.     

Influence of the yeast strain on Monastrell wine colour

Two commercial yeast strains were assayed during the winemaking process of Monastrell grapes to determine their influence on colour and phenolic composition of the resulting wines during alcoholic fermentation and maturation. The results showed that in 2002, the wines did not present great differences but in 2003 higher colour intensity and phenolic compounds content were detected when one of the commercial strains was used. A discriminant statistical analysis clearly showed that different yeasts led to different wines as regard their chromatic characteristics.Industrial relevanceThe importance of yeast in winemaking is extensively known since they are responsible for the transformation of sugars into ethanol and for the formation of the most significant aroma compounds in wines. However, they may also participate in wine colour and this role is usually not taken into account in the wine industry. The choice of a yeast strain is an important factor since these microorganisms have the capacity to retain or adsorb phenolic compounds and, on the other hand, yeast may contribute to stabilizing wine colour, as a result of participating in the formation of vitisins during fermentation or liberating mannoproteins that have the capacity to bind to anthocyanins and tannins, protecting them from precipitation. Two commercial yeast strains were assayed during the winemaking process of Monastrell grapes to determine their influence on colour and phenolic composition of the resulting wines during alcoholic fermentation and maturation. The results showed that higher colour intensity and phenolic compounds content were detected when one of the commercial strains was used, both during fermentation and wine aging, and may be used as a tool during winemaking for obtaining stable and highly coloured wines.     

不同酵母对干白葡萄酒发酵过程中香气变化的影响

选用两种酿酒酵母进行霞多丽干白葡萄酒发酵试验,酒精发酵过程中对发酵液的还原糖、可溶性固形物、总酸含量及香气物质进行分析。结果表明,两种酿酒酵母发酵过程中发酵液的还原糖和可溶性固形物均呈下降趋势,总酸含量均大于葡萄汁总酸含量;葡萄汁和发酵液中共检测出68种香气物质。相比于葡萄汁,酵母LA-DE和LA-PE发酵时发酵液中醇类、酯类、酸类、萜烯类和酚类物质含量随发酵时间延长逐渐增加,而醛类物质逐渐减少;其中酯类物质含量增加显著,发酵结束时分别为22.79 mg/L和14.57 mg/L。主成分分析结果表明,发酵过程中香气物质在前3 d变化较为明显,两种酵母发酵液在第1天、第3天、第9天香气物质差异明显。     

白兰地中香气成分的来源及陈酿期间香气物质变化研究进展

近年来随着白兰地市场规模的扩大,消费者对白兰地品质的要求也越来越高,其中白兰地中的香气成分是评价白兰地酒品质的一个重要感官指标。该文对白兰地中的香气来源进行综述,从葡萄原料、酵母发酵和橡木桶陈酿三个方面分别总结了白兰地中醇类、酸类、酯类、羰基化合物、苯酚化合物、氮化合物、萜烯化合物及其他香气化合物的来源,重点阐述了产地微生物包括酿酒酵母和非酿酒酵母等对于白兰地基酒的理化、香气等感官指标的影响以及陈酿期间的一系列化学反应和物质变化,同时也对超高压等催陈技术在白兰地陈酿过程中的作用和前景进行了探究,以期为生产具有产地特色的优质高端白兰地提供参考,对于提升我国白兰地的品质和市场竞争力具有重要意义。     

橡木片对霞多丽葡萄酒发酵的影响

该文研究在发酵过程中添加法国中度烘烤橡木制品对霞多丽干白葡萄酒的影响,增加霞多丽干白葡萄酒酿造工艺的选择性.接种酵母菌进行酒精发酵的同时在葡萄汁中添加法国中度烘烤橡木制品,未添加橡木制品发酵的样品为对照样,分别在发酵降糖50％和酒精发酵结束时测定理化指标、有机酸与挥发性化合物的含量.结果表明:添加橡木制品发酵对霞多丽葡萄酒化学物质有一定影响,其总高级醇、总橡木挥发性化合物含量较高.而对照样的葡萄酒中总酸和总酯含量较高,总高级醇含量是添加橡木制品发酵的葡萄酒中总高级醇含量的70％～85％,而酸类物质含量是添加橡木制品发酵葡萄酒的2倍.