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.     

戴尔有孢圆酵母对葡萄酒香气的影响

以新疆天山北麓产区和山东乳山产区赤霞珠葡萄为原料,分别选用酿酒酵母、戴尔有孢圆酵母单独发酵以及二者混合发酵,发酵结束后测定葡萄酒的各项理化指标以及挥发性化合物含量。结果表明：2个产地赤霞珠葡萄酒共检测出60种与酵母代谢相关的挥发性化合物,其中醇类23种、酯类26种、酸类8种和酮类3种,不同酵母菌发酵的葡萄酒中的香气成分及含量差异明显;戴尔有孢圆酵母单独发酵产生的醇类、酯类和酸类含量都较高,而与酿酒酵母混合发酵则降低了挥发酸的含量;本实验中戴尔有孢圆酵母明显提高了赤霞珠葡萄酒中乙基酯类的含量,特别是辛酸乙酯、癸酸乙酯和月桂酸乙酯等脂肪酸乙酯,增加了葡萄酒中的果香味;对于原料来自不同产地的葡萄酒,戴尔有孢圆酵母与酿酒酵母混合发酵均可以增强其发酵香气,提高葡萄酒香气的复杂性。     

Comparison of amino acids,biogenic amines and ammonium ion of wines made of different types of fruits

Amino acids, biogenic amines and ammonium ion are the primary nitrogen sources in fruit wines. Compared to grape wines, our knowledge to their profile in wines made of other fruits is very lack. Fourteen wines made of nine kinds of fruits together with seven grape wines were selected to compare their nitrogen component profile. White grape wines possessed the highest level of total amino acids, followed by red grape wines and then the wines made of the other fruits. Red grape wines contained the highest level of biogenic amines, followed by white grape wines and the wines made of the other fruits. Ammonium ion was also found to be higher in the wines made of grapes. Principal component analysis revealed that the obvious separations existed among the wines made from different types of fruits, indicating that these nitrogen compounds could be served as the indicators to differentiate different types of fruit wines.     

Vinification Effects on Changes in Volatile Compounds of Wine

Alcohols, esters and fatty acids in wines from red, rose and carbonic maceration of Monastrell grapes were measured during yeast fermentation. Isolated volatile compounds were analyzed by gas chromatography alone and with-mass spectrometry. Increases in these compounds was most important during the first days of fermentation and concentrations varied between vinifications. The lower fermentation temperature and shorter skin contact time of rose vinification produced higher concentrations of esters and acids than in red wine. The intracellular fermentation in carbonic maceration vinification resulted in formation of almost all esters and fatty acids before alcoholic fermentation started. The final wine was closer to rose than red wine in aromatic composition.     

顶空固相微萃取-气相色谱质谱联用技术比较赤霞珠干化葡萄和干化葡萄酒香气成分

采用顶空固相微萃取-气相色谱质谱联用技术,对赤霞珠干化葡萄和干化葡萄酒香气成分进行分析比较。检测出干化赤霞珠葡萄的香气成分34种,包括12种醇类、8种酯类、5种有机酸、5种醛类和4种其他类物质;干化葡萄酒得到香气成分45种,包括16种醇类、22种酯类、5种有机酸、2种酮类。     

Comparison of major volatile compounds from Riesling and Cabernet Sauvignon grapes (Vitis vinifera L.) from fruitset to harvest

Background and Aims: Research on concentration changes of volatile compounds during grape physiological development has focused on the period from veraison to harvest. This study compared the developmental changes in the major volatile compounds released after the crushing of Riesling and Cabernet Sauvignon grapes sampled from fruitset to harvest during the 2007–2008 season. Methods and Results: Volatile compounds were extracted from the headspace of crushed Riesling and Cabernet Sauvignon grapes sampled throughout berry development using solid-phase microextraction and analysed by gas chromatography–mass spectrometry. A multivariate statistical approach coupled with analysis of variance was applied to compare the developmental changes in volatile compounds for the two cultivars. In both cultivars, E-2-hexenal was the most abundant volatile compound, and it showed a significant increase in concentration after veraison. Benzene derivatives discriminated ripe Cabernet Sauvignon grapes, whereas monoterpenes and sesquiterpenes discriminated both cultivars pre-veraison with a broader range of terpenes observed in the Cabernet Sauvignon samples compared with the Riesling samples. At veraison, terpene production in both varieties was low, but Riesling grapes produced some terpenes (geraniol and α-muurolene) post-veraison. Generally, esters and aldehydes were the major class of compounds from Riesling grapes, while Cabernet Sauvignon showed a greater tendency to form alcohols. Conclusions: Both Riesling and Cabernet Sauvignon grapes had a more complex volatile compound composition pre-veraison than post-veraison. This study suggests that some compounds that contribute to grape aroma may be produced pre-veraison, and not simply accumulate after veraison. Significance of the Study: Understanding the timing of volatile compound production and cultivar differences will guide viticulture researchers and growers in the optimisation of vineyard strategies to enhance grape aroma attributes that may, in turn, contribute to wine aroma.     

Influence of sour rotten grapes on the chemical composition and quality of grape must and wine

This study evaluated the effect of grape sour rot on wine fermentation and characterized the chemical composition and the sensory changes in wines produced from rotten musts. Microvinifications were performed during two vintages using healthy Trincadeira and Cabernet Sauvignon red grape varieties to which were added grapes affected by sour rot. Increasing sour rot percentages, up to 50%, contributed to a clear decrease in free run must and final wine yields and induced significant changes in grape must chemical composition expressed by the increase in sugar content, total acidity, volatile acidity, anthocyanins, total phenols, and color intensity. After malolactic fermentation, wines from rotten grapes showed higher values of alcohol content, dry extract, reducing sugar content, total and volatile acidity, anthocyanins, total phenols, and color intensity. Despite the higher levels of reducing sugars, the microbial stability was similar to that of healthy wines. The sensorial evaluation, after malolactic fermentation, showed that both types of wine were not statistically different regarding color, aroma, taste, and overall quality. During 6–8 month storage, wines from rotten grapes showed a significant higher percentage of color loss, suggesting that sour rot is responsible for the decrease in color stability. Nevertheless, the results of sensorial analysis demonstrated that the fermentation of grape musts containing up to 30% sour rot yields wines with similar or even higher-quality scores than wines made with healthy grapes.     

Influence of Nutrients Addition to Nonlimited-in-Nitrogen Must on Wine Volatile Composition

ABSTRACT: Several factors can affect production of volatile compounds in wines, including nutritional differences in the must. Among the nutritive compounds of must, the amino acids are of great importance due to the fact that they can serve as precursors of esters or may play an indirect role in supporting cellular metabolic activities. The aim of this study was to examine the influence of the addition of a complex nutrient such as the yeast autolysate to a nitrogen nonlimited must of Chardonnay variety on the formation of esters, alcohols, and acids. Yeast autolysate supplied fatty acids, amino acids (above all, tyrosine, threonine, and glutamic acid), and an insoluble fraction formed by yeast cell walls. It was observed that the nutrient enrichment of the Chardonnay must did not favor the formation of either esters or alcohols. These results demonstrate that when juice is sufficient in nitrogen, the addition of amino acids does not improve the volatile composition of wine. Under these conditions, the amino acids would have probably been used for other cellular processes that do not produce volatile compounds.     

Different commercial yeast strains affecting the volatile and sensory profile of cava base wine

36 semi-industrial fermentations were carried out with 6 different yeast strains in order to assess differences in the wines' chemical and volatile profile. Two of the tested strains (Y3 and Y6) showed the fastest fermentation rates throughout 3 harvests and on 2 grape varieties. The wines fermented by three of the tested strains (Y5, Y3 and Y4) stand out for their high amounts of esters and possessed the highest fruity character. Wines from strains producing low amounts of esters and high concentrations of medium chain fatty acids, higher alcohols and six-carbon alcohols were the least appreciated at the sensory analysis. The data obtained in the present study show how the yeast strain quantitatively affects the final chemical and volatile composition of cava base wines and have repercussions on their sensory profile, independently of must variety and harvest year.     

Effect of ripening stage of grapes on the low molecular weight phenolic compounds of red wines

Different red wines were elaborated to study the effect of the date of the grape harvest on the levels of individual low molecular weight phenolic compounds, which are chiefly responsible for the wine color. Two red grape varieties and two consecutive years were studied at three different harvesting stages of grapes, and the changes during the 18 months of wine aging (12 months in oak barrels and 6 months in the bottle) were also followed. The results showed that the wines made from grapes harvested 1 week later than the usual date generally had higher contents of some simple phenols, which can act as cofactors that can maintain the color intensity and violet tonalities in aged wines. Besides, these wines had lower levels of caftaric and coutaric acids, which are two of the main substrates for oxidation and browning processes.     

A review of the analytical methods to determine organic acids in grape juices and wines

The determination of low molecular weight organic acids in grape juices and wines is important because of their influence in organoleptic properties (flavour, colour and aroma) and in the stability and microbiologic control of these beverages. The analysis of these acids allows to check the process of maturation of grapes and to control the evolution of the acidity of wines during the several stages of their elaboration process (alcoholic fermentation, malolactic fermentation, aging process, etc).

In this work, a comprehensive review of the analytical methods developed for the determination of short-chain organic acids in grape juices and wines has been shown. This review included non-enzymatic spectrophotometric, enzymatic, chromatographic and electrophoretic methods. Details of the chromatographic and electrophoretic conditions of these methods have been collected in tables.     

不同品种葡萄皮渣蒸馏酒挥发性香气成分分析

采用顶空固相微萃取-气相色谱-质谱联用（HS-SPME-GC-MS）技术对3种葡萄（贵人香、雷司令、霞多丽）皮渣蒸馏酒的挥发性香气成分进行检测分析。结果表明,从3种葡萄皮渣蒸馏酒中共检测出114种挥发性香气化合物,包括酯类40种、醇类23种、酸类8种、醛类4种、酮类2种、酚类2种、萜烃类24种、其他类11种,其中酯类、醇类和萜烃类挥发性化合物相对含量较高,且贵人香皮渣蒸馏酒的香气成分种类更为丰富。为进一步研究香气化合物与葡萄皮渣品种的关系,对3种葡萄皮渣蒸馏酒样共有的22种香气成分和8类香气化合物进行主成分分析（PCA）,经综合评价得出贵人香葡萄皮渣蒸馏酒香气品质最佳,雷司令葡萄皮渣蒸馏酒次之,霞多丽葡萄皮渣蒸馏酒最差。     

Volatile profile and differentiation between Albariño wines from different origins

Commercial Albariño wines from different subzones of Certified Brand of Origin ‘Rías Baixas’ (NW Spain) were analysed over four consecutive harvests. The contents of monoterpenes, volatile phenols, alcohols, sulphur compounds, acetates, fatty acids and ethyl esters were determined by gas chromatography (flame ionisation detector and flame photometric detector) and gas chromatography–mass spectrometry. These white wines presented high concentrations of free monoterpenes, volatile phenols, acetates, and ethyl esters, while the levels of sulphur compounds, known as default compounds, were very low. All the wines were elaborated from Albariño grapes, but they were produced by different enological practices, such as skin contact and by carrying out malolactic fermentation or not. No significant differences were found between wines from the same subzone and from different vintages. The results obtained, and confirmed by Principal component and linear discriminant analysis, showed a differentiation among these wines as a function of the Galician subzone of origin.     

Discovering a chemical basis for differentiating wines made by fermentation with 'wild' indigenous and inoculated yeasts: role of yeast volatile compounds

Background and Aims:  Winemakers are constantly searching for new techniques to modulate wine style. Exploiting indigenous yeasts present in grape must is re-emerging as a commercial option in New World wine regions. Wines made with indigenous or 'wild' yeasts are perceived to be more complex by showing a greater diversity of flavours; however, the chemical basis for the flavour characteristics is not yet defined. In order to evaluate techniques for making wine with the 'wild yeast fermentation' character more reliably, it is necessary to define the salient chemical characteristics of such wines.
Methods and Results:  Pairs of Chardonnay wines were prepared from the same must and subjected to similar fermentation conditions in the wineries of origin, except for the mode of inoculation. Reference wines were made by inoculation with a Saccharomyces cerevisiae starter culture, whereas companion wines were allowed to undergo fermentation with the indigenous microflora. Of all wine chemicals analysed, only yeast-derived volatile fermentation products showed significant differences between the yeast treatments.
Conclusions:  Inoculated wines were associated with the esters ethyl hexanoate and 3-methylbutyl acetate and formed a clear cluster by principal component analysis. By comparison with inoculated wines, 'wild' yeast fermented wines showed high variability in volatile compounds that contribute to wine aroma, with higher concentrations of 2-methylpropanol, 2-methylbutanoic acid, ethyl 2-methylpropanoate, ethyl decanoate and ethyl dodecanoate potentially being sensorially important.
Significance of the Study:  This study shows that yeast-derived volatile fermentation products are a key difference between inoculated and uninoculated ferments and provides a chemical basis for the 'wild yeast fermentation' character.     

Induction of grape botrytization during withering affects volatile composition of Recioto di Soave, a “passito”-style wine

The influence of noble rot on the quality of Recioto di Soave, a “passito” sweet white wine, is greatly variable depending on the occurrence of favourable seasonal conditions for the mould infection. Botrytized wines were produced from grapes inoculated with conidia suspensions to evaluate the effects of noble rot on volatile compounds profile of Recioto di Soave wine. Different development stages of Botrytis cinerea and degree of grape withering were ascertained by must analysis. Several volatile components were involved in marked changes depending on the infection and grape withering level. Fruity esters, carbonyl compounds, phenols, lactones and acetamides greatly changed among botrytized wines. The results demonstrated that the level of B. cinerea infection and the degree of grape withering exert considerable influence on the volatile composition of this sweet wine. Strain-dependent effects were also preliminary ascertained. The process of induction of grape botrytization presented in this study could be recommendable for the industrial production of botrytized Recioto di Soave wine.     

Development changes of anthocyanins in Vitis vinifera grapes grown in the Douro Valley and concentration in respective wines

Grapes of Touriga Nacional and Touriga Francesa red Vitis vinifera varieties have been sampled from two vineyard sites at different altitudes during three consecutive vintage years (1997, 1998 and 1999) in the Douro Valley. The total anthocyanidin monoglucosides (AMGs) detected by HPLC/DAD and the red colour of grape skin extracts were monitored during the last month of maturation. Microvinifications were performed with the grapes studied and the resulting Port wines were analysed. Malvidin 3‐glucoside and its acylated esters were the major AMGs irrespective of cultivar at harvest date. Vineyard altitude, together with other variables, was found to be an important factor contributing to the amount of anthocyanin compounds found in grapes of Touriga Nacional and Touriga Francesa. Overall, the climatic conditions observed at higher vineyard sites appeared to be advantageous, resulting in larger amounts of AMGs in grapes. The same outcome was obtained in the resulting wines, which showed higher levels of AMGs when made from grapes grown at higher altitude, especially for Touriga Francesa. © 2002 Society of Chemical Industry     

Binding capacity of brown pigments present in special Spanish sweet wines

Some special Spanish sweet wines are obtained by addition of a sweetening and coloring agent called grape syrup, which is obtained by heating must to give a dark and highly caramelised liquid, with similar consistency than other syrups. The aim of this work was to establish the influence of the addition of boiled must or “grape syrup” on the aroma and colour of sweet wines focussing specially on the possible binding effect on volatile compounds. The influence of must polyphenols was also studied, so, a wine sweetened with a “grape syrup” free of polyphenols was also elaborated. As it was expected, the addition of grape syrups gave an increase in the levels of furfural related compounds, and sweet wines showed lower concentrations of terpenes, ethyl esters, organic acids and acetates of alcohols than the control wine. The capacity of brown polymers present in grape syrups to bind these volatile compounds is discussed. Furthermore, colour parameters were also studied and significant differences were found for all of them between sweet wines and control wine.     

Application of foliar urea to grapevines: productivity and flavour components of grapes

Urea is a non-electrically charged nitrogen (N) molecule suitable for foliar application, since it easily penetrates the epicuticular waxes and the cutin layer of leaves. Several field trials have been conducted to understand how foliar application of urea to grapevines may affect yield and grape composition compared to other N fertilisers. The effectiveness of foliar application of urea to change the flavour components of grapes depends on the N status of the grapevines related to crop load and the timing of the foliar application, which could also play a key role in basal bud fertility and stored N reserves. The application of foliar urea to grapevines may affect the concentration of N, volatile compounds, and phenolic substances in grapes without influencing yield and its components in the short term. During alcoholic fermentation, grape N concentration favours the production of non-volatile and volatile compounds that affect wine attributes, aroma, bitterness, and astringency. Other N-compounds such as biogenic amines may also be formed in wines which can be toxic to the consumer. Gene expression related to grapevine N metabolism and the identification of putative chemical markers in red and white wines after foliar N application deserves further investigation. This review aimed to evaluate the factors involved in N uptake by leaves after foliar urea fertilisation, to summarise effects on grapevine yield components and grape composition and to provide also research options for future studies in this area.     

Applications of an oak extract on Petit Verdot grapevines. Influence on grape and wine volatile compounds

Petit Verdot vineyards were treated at veraison with a commercial aqueous French oak extract in order to determine if the extract’s volatile components can be transferred to grapes and then to wines. Three different formulations (25% (one application), 25% (four applications) and 100%) were tested, together with an eugenol and guaiacol standard solution to better follow their behaviour. The volatile compounds of treated grapes and their wines after alcoholic and malolactic fermentation and after 8 months were analysed by stir bar sorptive extraction and gas chromatography mass spectrometry (SBSE-GC–MS). The results showed that the grapes stored the volatile compounds mainly as non-volatile precursors, and some of these were released after winemaking. In the case of wines, it was possible to distinguish the control versus the ones from vineyard treatments. The different oak extract applications were evident only after alcoholic fermentation sampling, making it very interesting for young wines.     

Influence of addition of ammonium and different amino acid concentrations on nitrogen metabolism in spontaneous must fermentation

The effect of the addition of different amino acid concentrations in must on yeast nitrogen metabolism during alcoholic fermentation was studied. To do this, fermentations of Mazuelo must, poor in nitrogen compounds, were carried out. Ammonium and different concentrations of amino acids (0, 45, 120, 250 and 450 mg/l) were added to the must. Addition of 45, 120 and 250 mg/l of proteic amino acids to the must increased the rate of fermentation. Proline was mainly consumed in fermentations with smaller amounts of amino nitrogen and, at the same time, this amino acid showed the highest residual concentration in the final wines. The consumption of other proteic amino acids was directly proportional to their concentration in the musts, with the exception of leucine and isoleucine that were synthesized. However, a difference in the percentages of the amino acids consumed by the yeasts was observed. The percentages of aspartic acid, alanine and arginine consumed were higher in the fermentations supplemented with amino acids than in the fermentation where only ammonium was added. The percentages of tyrosine and phenylalanine consumed gradually increased with increase of their initial concentration.