Impact of different malolactic fermentation inoculation scenarios on Riesling wine aroma

During malolactic fermentation (MLF), lactic acid bacteria influence wine aroma and flavour by the production of volatile metabolites and the modification of aroma compounds derived from grapes and yeasts. The present study investigated the impact of different MLF inoculation strategies with two different Oenococcus oeni strains on cool climate Riesling wines and the volatile wine aroma profile. Four different timings were chosen for inoculation with bacteria to conduct MLF in a Riesling must/wine with a high acidity (pH 2.9–3.1). Treatments with simultaneous inoculation showed a reduced total fermentation time (alcoholic and malolactic) compared to the sequential inoculations. No negative impact of simultaneous alcoholic and malolactic fermentation on fermentation success and on the final wine volatile aroma composition was observed. Compared to sequential inoculation, wines with co-inoculation tended to have higher concentrations of ethyl and acetate esters, including acetic acid phenylethylester, acetic acid 3-methylbutylester, butyric acid ethylester, lactic acid ethylester and succinic acid diethylester. Results of this study provide some alternatives to diversify the number of wine styles by safely conducting MLF in low-pH, cool-climate white musts with potential high alcohol content.     

Bioconversion of lutein using a microbial mixture—maximizing the production of tobacco aroma compounds by manipulation of culture medium

The generation of aroma compounds by carotenoid cleavage in the 9–10 position was studied, due to the importance of these compounds in the flavor and fragrance industry. The bioconversion of the carotenoid lutein to C₁₃ norisoprenoids utilizing a microbial mixture composed of Trichosporon asahii and Paenibacillus amylolyticus was carried out by a fermentation process. Applying an experimental design methodology, the effects of nutritional factors on the production of aroma compounds present in the tobacco profile were studied. After an assessment of the significance of each nutritional factor, the levels of the variables yielding the maximum response were calculated. Glucose, tryptone, and yeast extract exerted a strong negative effect over the objective function, with glucose being the strongest. Lutein possessed a positive effect over the tobacco aroma production, while sodium chloride and trace elements showed no influence over the process. The yield attained after culture medium manipulation was almost ten-fold higher, compared with the base medium; and the aroma mixture was characterized as: 7,8-dihydro--ionol (95.2%), 7,8-dihydro--ionone (3.7%), and -ionone (1.1%).     

Effect of Increased Yeast Alcohol Acetyltransferase Activity on Flavor Profiles of Wine and Distillates

The distinctive flavor of wine, brandy, and other grape-derived alcoholic beverages is affected by many compounds, including esters produced during alcoholic fermentation. The characteristic fruity odors of the fermentation bouquet are primarily due to a mixture of hexyl acetate, ethyl caproate (apple-like aroma), iso-amyl acetate (banana-like aroma), ethyl caprylate (apple-like aroma), and 2-phenylethyl acetate (fruity, flowery flavor with a honey note). The objective of this study was to investigate the feasibility of improving the aroma of wine and distillates by overexpressing one of the endogenous yeast genes that controls acetate ester production during fermentation. The synthesis of acetate esters by the wine yeast Saccharomyces cerevisiae during fermentation is ascribed to at least three acetyltransferase activities, namely, alcohol acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT. To investigate the effect of increased AAT activity on the sensory quality of Chenin blanc wines and distillates from Colombar base wines, we have overexpressed the alcohol acetyltransferase gene (ATF1) of S. cerevisiae. The ATF1 gene, located on chromosome XV, was cloned from a widely used commercial wine yeast strain of S. cerevisiae, VIN13, and placed under the control of the constitutive yeast phosphoglycerate kinase gene (PGK1) promoter and terminator. Chromoblot analysis confirmed the integration of the modified copy of ATF1 into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression of ATF1 at high levels in these yeast transformants. The levels of ethyl acetate, iso-amyl acetate, and 2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature, cultivar, and yeast strain used. The concentrations of ethyl caprate, ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect on the solvent or chemical aroma (associated with ethyl acetate and iso-amyl acetate) and the herbaceous and heads-associated aromas of the final distillate and the solvent or chemical and fruity or flowery characters of the Chenin blanc wines. This study establishes the concept that the overexpression of acetyltransferase genes such as ATF1 could profoundly affect the flavor profiles of wines and distillates deficient in aroma, thereby paving the way for the production of products maintaining a fruitier character for longer periods after bottling.     

Analysis of volatile aroma constituents of wine produced from Indian mango (<Emphasis Type="Italic">Mangifera indica</Emphasis> L.) by GC-MS

Volatile aroma compounds are synthesized by wine yeast during wine fermentation. In this study the volatile aroma composition of two varieties of mango wine were determined to differentiate and characterize the wines. The wine was produced from the fruits of two varieties of mango cultivars namely Banginapalli and Alphonso. The volatile compounds formed in mango wine were analyzed by gas chromatography coupled with mass spectrometry (GC-MS). Thirty-two volatile compounds in wines were determined of which four were new and unidentified present in lower concentration. Apart from the ethanol (8.5 ± 0.28 and 7.2 ± 0.28% v/v), 1-propanol (54.11 ± 0.33 and 42.32 ± 0.57 mg/l), isobutyl alcohol (102 ± 1.57 and 115.14 ± 2.88 mg/l) and isoamyl alcohol (123 ± 2.88 and 108.40 ± 0.23 mg/1) were found to be the major flavouring higher alcohols in the mango wines produced from the fruits of Banginapalli and Alphonso respectively. Ethyl acetate (35 ± 0.57 and 30.42 ±1.15 mg/l) was the major ester component in both wines produced. Besides, other esters like ethyl octonoate, ethyl hexanoate and ethyl decanoate were also present in the wines. Cyclohexane methanol (1.45 ± 0.11 mg/l) was present only in wine made from Banginapalli and β-phenylethyl butanoate (0.62 ± 0.01 mg/1) was found only in Alphonso wine. The results demonstrate that the wine prepared from Banginapalli variety had better aroma composition and good taste than that from the Alphonso variety.     

Carotenoid‐Cleavage Activities of Crude Enzymes from Pandanous amryllifolius

Carotenoid degradation products, known as norisoprenoids, are aroma‐impact compounds in several plants. Pandan wangi is a common name of the shrub Pandanus amaryllifolius. The genus name ‘Pandanus’ is derived from the Indonesian name of the tree, pandan. In Indonesia, the leaves from the plant are used for several purposes, e.g., as natural colorants and flavor, and as traditional treatments. The aim of this study was to determine the cleavage of β‐carotene and β‐apo‐8′‐carotenal by carotenoid‐cleavage enzymes isolated from pandan leaves, to investigate dependencies of the enzymatic activities on temperature and pH, to determine the enzymatic reaction products by using Headspace Solid Phase Microextraction Gas Chromatography/Mass Spectrophotometry (HS‐SPME GC/MS), and to investigate the influence of heat treatment and addition of crude enzyme on formation of norisoprenoids. Crude enzymes from pandan leaves showed higher activity against β‐carotene than β‐apo‐8′‐carotenal. The optimum temperature of crude enzymes was 70°, while the optimum pH value was 6. We identified β‐ionone as the major volatile reaction product from the incubations of two different carotenoid substrates, β‐carotene and β‐apo‐8′‐carotenal. Several treatments, e.g., heat treatment and addition of crude enzymes in pandan leaves contributed to the norisoprenoid content. Our findings revealed that the crude enzymes from pandan leaves with carotenoid‐cleavage activity might provide a potential application, especially for biocatalysis, in natural‐flavor industry.     

Study of 'Redhaven' peach and its white-fleshed mutant suggests a key role of CCD4 carotenoid dioxygenase in carotenoid and norisoprenoid volatile metabolism

Background  

Carotenoids are plant metabolites which are not only essential in photosynthesis but also important quality factors in determining the pigmentation and aroma of flowers and fruits. To investigate the regulation of carotenoid metabolism, as related to norisoprenoids and other volatile compounds in peach (Prunus persica L. Batsch.), and the role of carotenoid dioxygenases in determining differences in flesh color phenotype and volatile composition, the expression patterns of relevant carotenoid genes and metabolites were studied during fruit development along with volatile compound content. Two contrasted cultivars, the yellow-fleshed 'Redhaven' (RH) and its white-fleshed mutant 'Redhaven Bianca' (RHB) were examined.     

Effect of increased yeast alcohol acetyltransferase activity on flavor profiles of wine and distillates

The distinctive flavor of wine, brandy, and other grape-derived alcoholic beverages is affected by many compounds, including esters produced during alcoholic fermentation. The characteristic fruity odors of the fermentation bouquet are primarily due to a mixture of hexyl acetate, ethyl caproate (apple-like aroma), iso-amyl acetate (banana-like aroma), ethyl caprylate (apple-like aroma), and 2-phenylethyl acetate (fruity, flowery flavor with a honey note). The objective of this study was to investigate the feasibility of improving the aroma of wine and distillates by overexpressing one of the endogenous yeast genes that controls acetate ester production during fermentation. The synthesis of acetate esters by the wine yeast Saccharomyces cerevisiae during fermentation is ascribed to at least three acetyltransferase activities, namely, alcohol acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT. To investigate the effect of increased AAT activity on the sensory quality of Chenin blanc wines and distillates from Colombar base wines, we have overexpressed the alcohol acetyltransferase gene (ATF1) of S. cerevisiae. The ATF1 gene, located on chromosome XV, was cloned from a widely used commercial wine yeast strain of S. cerevisiae, VIN13, and placed under the control of the constitutive yeast phosphoglycerate kinase gene (PGK1) promoter and terminator. Chromoblot analysis confirmed the integration of the modified copy of ATF1 into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression of ATF1 at high levels in these yeast transformants. The levels of ethyl acetate, iso-amyl acetate, and 2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature, cultivar, and yeast strain used. The concentrations of ethyl caprate, ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect on the solvent or chemical aroma (associated with ethyl acetate and iso-amyl acetate) and the herbaceous and heads-associated aromas of the final distillate and the solvent or chemical and fruity or flowery characters of the Chenin blanc wines. This study establishes the concept that the overexpression of acetyltransferase genes such as ATF1 could profoundly affect the flavor profiles of wines and distillates deficient in aroma, thereby paving the way for the production of products maintaining a fruitier character for longer periods after bottling.     

Introducing a New Breed of Wine Yeast: Interspecific Hybridisation between a Commercial Saccharomyces cerevisiae Wine Yeast and Saccharomyces mikatae

Interspecific hybrids are commonplace in agriculture and horticulture; bread wheat and grapefruit are but two examples. The benefits derived from interspecific hybridisation include the potential of generating advantageous transgressive phenotypes. This paper describes the generation of a new breed of wine yeast by interspecific hybridisation between a commercial Saccharomyces cerevisiae wine yeast strain and Saccharomyces mikatae, a species hitherto not associated with industrial fermentation environs. While commercially available wine yeast strains provide consistent and reliable fermentations, wines produced using single inocula are thought to lack the sensory complexity and rounded palate structure obtained from spontaneous fermentations. In contrast, interspecific yeast hybrids have the potential to deliver increased complexity to wine sensory properties and alternative wine styles through the formation of novel, and wider ranging, yeast volatile fermentation metabolite profiles, whilst maintaining the robustness of the wine yeast parent. Screening of newly generated hybrids from a cross between a S. cerevisiae wine yeast and S. mikatae (closely-related but ecologically distant members of the Saccharomyces sensu stricto clade), has identified progeny with robust fermentation properties and winemaking potential. Chemical analysis showed that, relative to the S. cerevisiae wine yeast parent, hybrids produced wines with different concentrations of volatile metabolites that are known to contribute to wine flavour and aroma, including flavour compounds associated with non-Saccharomyces species. The new S. cerevisiae x S. mikatae hybrids have the potential to produce complex wines akin to products of spontaneous fermentation while giving winemakers the safeguard of an inoculated ferment.     

软儿梨果酒发酵过程中挥发性风味物质变化分析

软儿梨是西北地区特有的一种“冻果”产品,酸甜可口、果香浓郁,是酿造果酒的上乘原料。为明确果酒发酵过程中果香的保留情况,并探究发酵时间的延长对软儿梨果酒品质的影响,以青海省民和县软儿梨冻果为原料,基于带皮渣发酵工艺,先采用顶空固相微萃取（solid?phase microextraction, SPME）,再结合气相色谱?质谱联用技术（gas chromatography?mass spectrometry, GC?MS）对原汁（0 d）、前发酵（7、14、28 d）、后发酵（100 d）3个不同时期样品中挥发性风味物质进行了动态跟踪分析,并结合相对气味活度值（relative odor activity value,ROAV）和主成分分析（principal component analysis,PCA）法分别探讨了软儿梨果酒原果香味保留情况和后发酵时间的延长对果酒风味的影响。结果显示：整个发酵过程共检出88种挥发性化合物,其中酯类33种、醇类29种、酸类6种、萜烯类7种以及13种其他类化合物,且风味物质的总含量随发酵的进行呈先上升后略有下降的趋势。ROAV结果表明：软儿梨原汁关键风味物质共8种,分别是丁酸乙酯、己酸乙酯、2?甲基丁酸乙酯、正辛醇、大马士酮、芳樟醇、丁香酚和癸醛;其中果香物质己酸乙酯、正辛醇、芳樟醇、丁香酚和大马士酮在果酒发酵中得到了很好的保留,是决定软儿梨果酒风味的关键物质。主成分分析表明：发酵初期主要的香气贡献物质是具有水果香的丁酸乙酯、3?羟基丁酸乙酯、2?甲基丁酸乙酯;发酵100 d时,乙酸乙酯、α?松油醇、柠檬烯和芳樟醇对香气贡献较大,这些香气化合物共同赋予软儿梨果酒幽香清雅、馥香浓郁的独特风味品质。研究获得了软儿梨果酒关键风味物质及其在不同发酵阶段特征风味物质的变化规律,可为研发高品质软儿梨果酒产品、改进软儿梨果酒发酵工艺提供理论支撑和参考。     

Engineering Saccharomyces cerevisiae to release 3-Mercaptohexan-1-ol during fermentation through overexpression of an S. cerevisiae Gene, STR3, for improvement of wine aroma

Sulfur-containing aroma compounds are key contributors to the flavor of a diverse range of foods and beverages. The tropical fruit characters of Vitis vinifera L. cv. Sauvignon blanc wines are attributed to the presence of the aromatic thiols 3-mercaptohexan-1-ol (3MH), 3-mercaptohexan-1-ol-acetate, and 4-mercapto-4-methylpentan-2-one (4MMP). These volatile thiols are found in small amounts in grape juice and are formed from nonvolatile cysteinylated precursors during fermentation. In this study, we overexpressed a Saccharomyces cerevisiae gene, STR3, which led to an increase in 3MH release during fermentation of a V. vinifera L. cv. Sauvignon blanc juice. Characterization of the enzymatic properties of Str3p confirmed it to be a pyridoxal-5'-phosphate-dependent cystathionine β-lyase, and we demonstrated that this enzyme was able to cleave the cysteinylated precursors of 3MH and 4MMP to release the free thiols. These data provide direct evidence for a yeast enzyme able to release aromatic thiols in vitro that can be applied in the development of self-cloned yeast to enhance wine flavor.     

Expression of the Malolactic Enzyme Gene (<Emphasis Type="Italic">mle</Emphasis>) from <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> Under Winemaking Conditions

Malolactic fermentation (MLF) plays an important role in the production of wine, especially red wines, resulting in microbial stability, deacidification, as well as contributing to the aroma profile. MLF can be influenced by a number of factors. In this study, the influence of pH and ethanol on expression of the structural malolactic enzyme gene (mle) from Lactobacillus plantarum was investigated in a synthetic wine media, as well as in wine using quantitative PCR. Expression of mle was shown to be inducible by the presence of malic acid, with increased expression in the middle of MLF. Expression of mle was also shown to be increased at low pH values and decreased in the presence of ethanol. This indicates the role of MLF in acid tolerance and the negative impact of ethanol on the completion of MLF. The results therefore provide further evidence that L. plantarum should be applied as co-inoculation for MLF where alcohol will initially not have a negative impact on the malic acid degradation.     

Selection and hybridization of wine yeasts for improved winemaking properties: Fermentation rate and aroma productivity

Three strains out of thirty-one wine yeasts (Saccharomyces cerevisiae) were selected for their good winemaking properties (fermentation rate, tolerance of sulfur dioxide, aroma productivity, wine quality) and genetic markers (KHR killer activity, galactose assimilation), and used for hybridization by spore to spore mating. Of the twelve hybrids produced, two, Hy17-108 (RIFY 1001 × RIFY 1067) and Hy41-308 (RIFY 1001 × RIFY 1065), were selected on the basis of a fermentation test. In experimental winemaking the two hybrids demonstrated improved aroma productivity for higher alcohols, aromatic esters and/or fatty acids, while their fermentation rate was nearly the same as that of the parental strains.     

Genetic Determinants of Volatile-Thiol Release by Saccharomyces cerevisiae during Wine Fermentation

Volatile thiols, particularly 4-mercapto-4-methylpentan-2-one (4MMP), make an important contribution to the aroma of wine. During wine fermentation, Saccharomyces cerevisiae mediates the cleavage of a nonvolatile cysteinylated precursor in grape juice (Cys-4MMP) to release the volatile thiol 4MMP. Carbon-sulfur lyases are anticipated to be involved in this reaction. To establish the mechanism of 4MMP release and to develop strains that modulate its release, the effect of deleting genes encoding putative yeast carbon-sulfur lyases on the cleavage of Cys-4MMP was tested. The results led to the identification of four genes that influence the release of the volatile thiol 4MMP in a laboratory strain, indicating that the mechanism of release involves multiple genes. Deletion of the same genes from a homozygous derivative of the commercial wine yeast VL3 confirmed the importance of these genes in affecting 4MMP release. A strain deleted in a putative carbon-sulfur lyase gene, YAL012W, produced a second sulfur compound at significantly higher concentrations than those produced by the wild-type strain. Using mass spectrometry, this compound was identified as 2-methyltetrathiophen-3-one (MTHT), which was previously shown to contribute to wine aroma but was of unknown biosynthetic origin. The formation of MTHT in YAL012W deletion strains indicates a yeast biosynthetic origin of MTHT. The results demonstrate that the mechanism of synthesis of yeast-derived wine aroma components, even those present in small concentrations, can be investigated using genetic screens.     

Genetic determinants of volatile-thiol release by Saccharomyces cerevisiae during wine fermentation

Volatile thiols, particularly 4-mercapto-4-methylpentan-2-one (4MMP), make an important contribution to the aroma of wine. During wine fermentation, Saccharomyces cerevisiae mediates the cleavage of a nonvolatile cysteinylated precursor in grape juice (Cys-4MMP) to release the volatile thiol 4MMP. Carbon-sulfur lyases are anticipated to be involved in this reaction. To establish the mechanism of 4MMP release and to develop strains that modulate its release, the effect of deleting genes encoding putative yeast carbon-sulfur lyases on the cleavage of Cys-4MMP was tested. The results led to the identification of four genes that influence the release of the volatile thiol 4MMP in a laboratory strain, indicating that the mechanism of release involves multiple genes. Deletion of the same genes from a homozygous derivative of the commercial wine yeast VL3 confirmed the importance of these genes in affecting 4MMP release. A strain deleted in a putative carbon-sulfur lyase gene, YAL012W, produced a second sulfur compound at significantly higher concentrations than those produced by the wild-type strain. Using mass spectrometry, this compound was identified as 2-methyltetrathiophen-3-one (MTHT), which was previously shown to contribute to wine aroma but was of unknown biosynthetic origin. The formation of MTHT in YAL012W deletion strains indicates a yeast biosynthetic origin of MTHT. The results demonstrate that the mechanism of synthesis of yeast-derived wine aroma components, even those present in small concentrations, can be investigated using genetic screens.     

Genetic screening of wine‐related enzymes in Lactobacillus species isolated from South African wines

Aims: The objective of this study was to investigate the presence of genes coding for enzymes of oenological relevance in wine Lactobacillus strains isolated from South African grape and wine samples during the 2001 and 2002 harvest seasons. Methods and Results: A total of 120 wine lactobacilli isolates belonging to Lactobacillus plantarum, Lactobacillus hilgardii, Lactobacillus brevis, Lactobacillus pentosus, Lactobacillus paracasei, Lactobacillus sakei and Lactobacillus paraplantarum were genetically screened for enzyme‐encoding genes using PCR with primers specific for β‐glucosidase, protease, esterase, citrate lyase and phenolic acid decarboxylase. The results of PCR screening showed that the Lactobacillus strains possessed different combinations of enzymes and that some strains did not possess any of the enzymes tested. Confirmation analysis with gene sequencing also showed high similarity of genes with those available in GenBank database. Conclusion: In this study, we have demonstrated the existence of genes coding for wine‐related enzymes in wine lactobacilli that could potentially hydrolyse wine precursors to positively influence wine aroma. Significance and Impact of the Study: An expansion of knowledge on the genetic diversity of wine‐associated lactic acid bacteria will enable the selection of novel malolactic fermentation starter cultures with desired oenological traits for the improvement of the organoleptic quality of the wine, and hence wine aroma.     

Molecular and biochemical diversity of Oenococcus oeni strains isolated during spontaneous malolactic fermentation of Malvasia Nera wine

The diversity of indigenous Oenococcus oeni strains was investigated by molecular and biochemical characterization of isolates from Malvasia Nera wine, an economically important red wine of the Salento Region (Apulia, Italy), during spontaneous malolactic fermentation (MLF). A total of 82 isolates of this species, identified by species-specific PCR and 16S rDNA sequence analysis, was molecularly characterized by the amplified fragment length polymorphism (AFLP) technique. Three main groups resulted from cluster analysis and showed intraspecific homology higher than 50%, and a total of seven subgroups, with similarity values ranged from 80% to 98%, were obtained within these groups. Enzymatic activities, such as esterase, β-glucosidase, protease, and the consumption rate of l-malic acid, citric acid, acetaldehyde and arginine were assessed in the representative strains, according to AFLP analysis. The results showed different enzymatic activities and consumption rates of the tested metabolites among the strains. No correlation between molecular and biochemical data was observed. The evidence of biochemical variability observed among Malvasia Nera strains demonstrated that the wine aroma can be modulated depending on the strains involved in MLF. Hence, the heterogeneity existing within natural O. oeni populations represents an interesting ecological source that can be useful for technological purposes.     

Characterization of volatile fraction of typical Irpinian wines fermented with a new starter yeast

Non-Saccharomyces yeasts are microorganisms that play an important role in the fermentation dynamics, compositions and flavour of wine. The aromatic compounds responsible for varietal aroma in wine are mainly terpenes, of which the most important group are the monoterpenes because of their volatility and odour if present in a free form. In fact, some terpenyl-glycosides do not contribute to the aroma unless they are hydrolysed. The glycosylated form of terpenes can be converted by hydrolysis with β-glycosidases produced by yeasts during the winemaking process, into aromatic compounds. In this study we utilized a non-Saccharomyces yeast, with a high extra-cellular glycosidase activity, isolated from grapes of cultivars typical of Irpinia region. This strain, identified as a Rhodotorula mucillaginosa (strain WLR12), was used to carry out an experimental winemaking process and the results were compared with those obtained with a commercial yeast starter. Chemical and sensorial analysis demonstrated that the wines produced with WLR12 strain had a more floral aroma and some sweet and ripened fruit notes compared to those obtained with commercial yeast. The data also showed an increasing of the free terpenes fraction that, however, did not significatively modify the bouquet of the wines.     

Newly generated interspecific wine yeast hybrids introduce flavour and aroma diversity to wines

Increasingly, winemakers are looking for ways to introduce aroma and flavour diversity to their wines as a means of improving style and increasing product differentiation. While currently available commercial yeast strains produce consistently sound fermentations, there are indications that sensory complexity and improved palate structure are obtained when other species of yeast are active during fermentation. In this study, we explore a strategy to increase the impact of non-Saccharomyces cerevisiae inputs without the risks associated with spontaneous fermentations, through generating interspecific hybrids between a S. cerevisiae wine strain and a second species. For our experiments, we used rare mating to produce hybrids between S. cerevisiae and other closely related yeast of the Saccharomyces sensu stricto complex. These hybrid yeast strains display desirable properties of both parents and produce wines with concentrations of aromatic fermentation products that are different to what is found in wine made using the commercial wine yeast parent. Our results demonstrate, for the first time, that the introduction of genetic material from a non-S. cerevisiae parent into a wine yeast background can impact favourably on the wine flavour and aroma profile of a commercial S. cerevisiae wine yeast.     

Wine flavor and aroma

The perception of wine flavor and aroma is the result of a multitude of interactions between a large number of chemical compounds and sensory receptors. Compounds interact and combine and show synergistic (i.e., the presence of one compound enhances the perception of another) and antagonistic (a compound suppresses the perception of another) interactions. The chemical profile of a wine is derived from the grape, the fermentation microflora (in particular the yeast Saccharomyces cerevisiae), secondary microbial fermentations that may occur, and the aging and storage conditions. Grape composition depends on the varietal and clonal genotype of the vine and on the interaction of the genotype and its phenotype with many environmental factors which, in wine terms, are usually grouped under the concept of “terroir” (macro, meso and microclimate, soil, topography). The microflora, and in particular the yeast responsible for fermentation, contributes to wine aroma by several mechanisms: firstly by utilizing grape juice constituents and biotransforming them into aroma- or flavor-impacting components, secondly by producing enzymes that transform neutral grape compounds into flavor-active compounds, and lastly by the de novo synthesis of many flavor-active primary (e.g., ethanol, glycerol, acetic acid, and acetaldehyde) and secondary metabolites (e.g., esters, higher alcohols, fatty acids). This review aims to present an overview of the formation of wine flavor and aroma-active components, including the varietal precursor molecules present in grapes and the chemical compounds produced during alcoholic fermentation by yeast, including compounds directly related to ethanol production or secondary metabolites. The contribution of malolactic fermentation, ageing, and maturation on the aroma and flavor of wine is also discussed.