Effects of harvest dates on microbial communities of ice grape skins from Xinjiang of China

Ice wine is a sweet dessert wine made from pressing grapes naturally frozen on the vines. The structure and metabolic characteristics of native microbial community dominated by organics and nutrients transformation in fermenting process of ice wine on the grape skin are likely to change due to climate events. Our objective was to evaluate the influence of harvest time on structure and metabolic characteristics of bacterial and fungal communities on Vidal ice grape surface. Vidal grape samples were picked between October and December in 2018; Harvest 1 (VG1): 14 October; Harvest 2 (VG2): 16 November; Harvest 3 (VG3): 18 December. Vishniacozyma, Alternaria, Cladosporium, Stenotrophomonas, unidentified_Cyanobacteria and Sphingomonas existed in all harvest dates and were the main genera widespread in most grape samples from the three harvest periods. Saprotrophic fungi and bacteria involved in metabolism were also dominant. For fungi, wood saprotrophs and unidentified saprotrophs were detected comprising Phoma, Didymella, Filobasidium and Clavaria. Delayed harvest of ice grapes has a distinct advantage for pathogen reduction compared with that of normally harvested grapes. Among bacteria, the most frequently occurring types in the metabolism category were energy metabolism, carbohydrate metabolism and lipid metabolism. In short, the harvest period can positively regulate the function of Vidal ice grape epidermal microorganisms.     

Evaluation of Non-Saccharomyces Yeasts for the Reduction of Alcohol Content in Wine

Over recent decades, the average ethanol concentration of wine has increased, largely due to consumer preference for wine styles associated with increased grape maturity; sugar content increases with grape maturity, and this translates into increased alcohol content in wine. However, high ethanol content impacts wine sensory properties, reducing the perceived complexity of flavors and aromas. In addition, for health and economic reasons, the wine sector is actively seeking technologies to facilitate the production of wines with lower ethanol content. Nonconventional yeast species, in particular, non-Saccharomyces yeasts, have shown potential for producing wines with lower alcohol content. These yeast species, which are largely associated with grapes preharvest, are present in the early stages of fermentation but, in general, are not capable of completing alcoholic fermentation. We have evaluated 50 different non-Saccharomyces isolates belonging to 24 different genera for their capacity to produce wine with a lower ethanol concentration when used in sequential inoculation regimes with a Saccharomyces cerevisiae wine strain. A sequential inoculation of Metschnikowia pulcherrima AWRI1149 followed by an S. cerevisiae wine strain was best able to produce wine with an ethanol concentration lower than that achieved with the single-inoculum, wine yeast control. Sequential fermentations utilizing AWRI1149 produced wines with 0.9% (vol/vol) and 1.6% (vol/vol) (corresponding to 7.1 g/liter and 12.6 g/liter, respectively) lower ethanol concentrations in Chardonnay and Shiraz wines, respectively. In Chardonnay wine, the total concentration of esters and higher alcohols was higher for wines generated from sequential inoculations, whereas the total concentration of volatile acids was significantly lower. In sequentially inoculated Shiraz wines, the total concentration of higher alcohols was higher and the total concentration of volatile acids was reduced compared with those in control S. cerevisiae wines, whereas the total concentrations of esters were not significantly different.     

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.     

Characterization of β-glucosidases from Hanseniaspora sp. and Pichia anomala with potentially aroma-enhancing capabilities in juice and wine

The properties of intracellular β-glucosidases produced from two yeast isolates identified as Hanseniaspora sp. BC9 and Pichia anomala MDD24 were characterized. β-Glucosidase from Hanseniaspora sp. BC9 was not inhibited by both 20% w/v fructose and 20% w/v sucrose and was slightly inhibited by glucose (> 40% relative β-glucosidase activity with 10% w/v glucose). β-Glucosidase from P. anomala MDD24 was inhibited by glucose, fructose and sucrose. In the presence of 4–12% v/v ethanol, β-glucosidase from P. anomala MDD24 was stimulated in range 110–130% relative activity whereas β-glucosidase from Hanseniaspora sp. BC9 was substantially inhibited in the presence of ethanol. Finally, juice and wine of the Muscat-type grape variety, Traminette, were selected to determine sugar-bound volatile aroma release, particularly terpenes, by the activity of those β-glucosidases. The results showed that high concentration of free aroma compounds were detected from Traminette juice treated with β-glucosidase from Hanseniaspora sp. BC9 and Traminette wine treated with β-glucosidase from P. anomala MDD24. The preliminary results with proposed an application of these enzymes in commercial wine production lead to more efficient of β-glucosidase from Hanseniaspora sp. BC9 in releasing desirable aromas during an early stage of alcoholic fermentation while β-glucosidase from P. anomala MDD24 is suitable at the final stage of alcoholic fermentation.     

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.     

Occurrence of Lactic Acid Bacteria During the Different Stages of Vinification and Conservation of Wines

We showed that the growth of lactic acid bacteria during alcoholic fermentation depends on the composition of the must. We illustrated how the addition of sulfur dioxide to the must before fermentation and the temperature of storage both affect the growth of these bacteria in the wine. Whereas species of Lactobacillus and Leuconostoc mesenteroides were isolated from grapes and must, Leuconostoc oenos was the only species isolated after alcoholic fermentation. This organism was responsible for the malolactic fermentation. Isolates of this species varied in their ability to ferment pentoses and hexoses. The survival of Leuconostoc oenos in wines after malolactic fermentation depended on wine pH, alcohol concentration, SO₂ concentration, and temperature of storage.     

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.     

Reduction of volatile acidity of acidic wines by immobilized Saccharomyces cerevisiae cells

Excessive volatile acidity in wines is a major problem and is still prevalent because available solutions are nevertheless unsatisfactory, namely, blending the filter-sterilized acidic wine with other wines of lower volatile acidity or using reverse osmosis. We have previously explored the use of an empirical biological deacidification procedure to lower the acetic acid content of wines. This winemaker’s enological practice, which consists in refermentation associated with acetic acid consumption by yeasts, is performed by mixing the acidic wine with freshly crushed grapes, musts, or marc from a finished wine fermentation. We have shown that the commercial strain Saccharomyces cerevisiae S26 is able to decrease the volatile acidity of acidic wines with a volatile acidity higher than 1.44 g?L^?1 acetic acid, with no detrimental impact on wine aroma. In this study, we aimed to optimize the immobilization of S26 cells in alginate beads for the bioreduction of volatile acidity of acidic wines. We found that S26 cells immobilized in double-layer alginate–chitosan beads could reduce the volatile acidity of an acidic wine (1.1 g?L^?1 acetic acid, 12.5 % (v/v) ethanol, pH 3.12) by 28 and 62 % within 72 and 168 h, respectively, associated with a slight decrease in ethanol concentration (0.7 %). Similar volatile acidity removal efficiencies were obtained in medium with high glucose concentration (20 % w/v), indicating that this process may also be useful in the deacidification of grape musts. We, therefore, show that immobilized S. cerevisiae S26 cells in double-layer beads are an efficient alternative to improve the quality of wines with excessive volatile acidity.     

Distribution and correlation of three oenological traits inSaccharomyces cerevisiae

The improvement of yeast starters for wine making, with classical genetic techniques, relays on the effective independence of the main oenological traits in order to combine them optimally. The analysis of three characters (ethanol production, volatile acidity and fermenting rate) in 787Saccharomyces cerevisiae strains, isolated from several parts of the world and substrates, shows moderate correlation between the volatile acidity and the other two traits, whereas ethanol production and fermenting rate appear more correlated. The minimum number of strains necessary to start selection or genetic improvement programs is discussed. The correlation between the oenological traits and the source of isolation showed that the best strains can be obtained from wineries and wine, whereas the isolates from grapes and must are less performing on the average.     

Grape and apple wines volatile fermentation products and possible relation to spoilage

The main volatile by-products of the alcoholic fermentation of grape wine, cider and apple pulp wine were investigated to determine if any correlated with spoilage resistance in the latter two. Spoilage was visually detected after seven days in low-alcohol grape wine in comparison to 11 and 16 days in cider and apple pulp wine, respectively. Acetaldehyde, ethyl acetate, methanol, propanol, isobutanol and amyl alcohols were the main fermentation by-products detected in all three wines. There were highest concentrations of acetaldehyde, ethyl acetate, methanol and propanol in grape wine and, therefore, these by-products could not be implicated in spoilage resistance in apple wines. Increased concentrations of isobutanol and amyl alcohols, however, in cider and apple pulp wine in comparison to grape wine might have been the reason for spoilage resistance in the apple wines.     

Contribution by Saccharomyces cerevisiae yeast to fermentative flavour compounds in wines from cv. Albariño

A comparative study was made of the fermentation products of Spanish Albariño wines produced with spontaneous yeast flora and an indigenous selected Saccharomyces cerevisiae strain (Alb16). The content of fermentative volatile compounds was determined by gas-chromatography-FID. Fifteen compounds (5 alcohols, 7 esters and 3 acetates) were identified in the two Albariño wines studied. Higher alcohols, ethyl esters (except ethyl hexanoate and ethyl octanoate) and acetates were in greater concentration in the spontaneous fermentation wine than in that with selected Alb16 strain. Principal components analysis showed good separation between the different wines.     

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.     

Microbial Species Diversity,Community Dynamics,and Metabolite Kinetics of Water Kefir Fermentation

Water kefir is a sour, alcoholic, and fruity fermented beverage of which the fermentation is started with water kefir grains. These water kefir grains consist of polysaccharide and contain the microorganisms responsible for the water kefir fermentation. In this work, a water kefir fermentation process was followed as a function of time during 192 h to unravel the community dynamics, the species diversity, and the kinetics of substrate consumption and metabolite production. The majority of the water kefir ecosystem was found to be present on the water kefir grains. The most important microbial species present were Lactobacillus casei/paracasei, Lactobacillus harbinensis, Lactobacillus hilgardii, Bifidobacterium psychraerophilum/crudilactis, Saccharomyces cerevisiae, and Dekkera bruxellensis. The microbial species diversities in the water kefir liquor and on the water kefir grains were similar and remained stable during the whole fermentation process. The major substrate, sucrose, was completely converted after 24 h of fermentation, which coincided with the production of the major part of the water kefir grain polysaccharide. The main metabolites of the fermentation were ethanol and lactic acid. Glycerol, acetic acid, and mannitol were produced in low concentrations. The major part of these metabolites was produced during the first 72 h of fermentation, during which the pH decreased from 4.26 to 3.45. The most prevalent volatile aroma compounds were ethyl acetate, isoamyl acetate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate, which might be of significance with respect to the aroma of the end product.     

Parameters Affecting Ethyl Ester Production by Saccharomyces cerevisiae during Fermentation

Volatile esters are responsible for the fruity character of fermented beverages and thus constitute a vital group of aromatic compounds in beer and wine. Many fermentation parameters are known to affect volatile ester production. In order to obtain insight into the production of ethyl esters during fermentation, we investigated the influence of several fermentation variables. A higher level of unsaturated fatty acids in the fermentation medium resulted in a general decrease in ethyl ester production. On the other hand, a higher fermentation temperature resulted in greater ethyl octanoate and decanoate production, while a higher carbon or nitrogen content of the fermentation medium resulted in only moderate changes in ethyl ester production. Analysis of the expression of the ethyl ester biosynthesis genes EEB1 and EHT1 after addition of medium-chain fatty acid precursors suggested that the expression level is not the limiting factor for ethyl ester production, as opposed to acetate ester production. Together with the previous demonstration that provision of medium-chain fatty acids, which are the substrates for ethyl ester formation, to the fermentation medium causes a strong increase in the formation of the corresponding ethyl esters, this result further supports the hypothesis that precursor availability has an important role in ethyl ester production. We concluded that, at least in our fermentation conditions and with our yeast strain, the fatty acid precursor level rather than the activity of the biosynthetic enzymes is the major limiting factor for ethyl ester production. The expression level and activity of the fatty acid biosynthetic enzymes therefore appear to be prime targets for flavor modification by alteration of process parameters or through strain selection.     

Generation of intra- and interspecific Saccharomyces hybrids with improved oenological and aromatic properties

Non-wine yeasts could enhance the aroma and organoleptic profile of wines. However, compared to wine strains, they have specific intolerances to winemaking conditions. To solve this problem, we generated intra- and interspecific hybrids using a non-GMO technique (rare-mating) in which non-wine strains of S. uvarum, S. kudriavzevii and S. cerevisiae species were crossed with a wine S. cerevisiae yeast. The hybrid that inherited the wine yeast mitochondrial showed better fermentation capacities, whereas hybrids carrying the non-wine strain mitotype reduced ethanol levels and increased glycerol, 2,3-butanediol and organic acid production. Moreover, all the hybrids produced several fruity and floral aromas compared to the wine yeast: β-phenylethyl acetate, isobutyl acetate, γ-octalactone, ethyl cinnamate in both varietal wines. Sc × Sk crosses produced three- to sixfold higher polyfunctional mercaptans, 4-mercapto-4-methylpentan-2-one (4MMP) and 3-mercaptohexanol (3MH). We proposed that the exceptional 3MH release observed in an S. cerevisiae × S. kudriavzevii hybrid was due to the cleavage of the non-volatile glutathione precursor (Glt-3MH) to detoxify the cell from the presence of methylglyoxal, a compound related to the high glycerol yield reached by this hybrid. In conclusion, hybrid generation allows us to obtain aromatically improved yeasts concerning their wine parent. In addition, they reduced ethanol and increased organic acids yields, which counteracts climate change effect on grapes.     

Evolution of the Lactic Acid Bacterial Community during Malt Whisky Fermentation: a Polyphasic Study

The development of the lactic acid bacterial community in a commercial malt whisky fermentation occurred in three broad phases. Initially, bacteria were inhibited by strong yeast growth. Fluorescence microscopy and environmental scanning electron microscopy revealed, in this early stage, both cocci and rods that were at least partly derived from the wort and yeast but also stemmed from the distillery plant. Denaturing gradient gel electrophoresis (DGGE) of partial 16S rRNA genes and sequence analysis revealed cocci related to Streptococcus thermophilus or Saccharococcus thermophilus, Lactobacillus brevis, and Lactobacillus fermentum. The middle phase began 35 to 40 h after yeast inoculation and was characterized by exponential growth of lactobacilli and residual yeast metabolism. Lactobacillus casei or Lactobacillus paracasei, L. fermentum, and Lactobacillus ferintoshensis were detected in samples of fermenting wort examined by DGGE during this stage. Bacterial growth was accompanied by the accumulation of acetic and lactic acids and the metabolism of residual maltooligosaccharides. By 70 h, two new PCR bands were detected on DGGE gels, and the associated bacteria were largely responsible for the final phase of the fermentation. The bacteria were phylogenetically related to Lactobacillus acidophilus and Lactobacillus delbrueckii, and strains similar to the former had previously been recovered from malt whisky fermentations in Japan. These were probably obligately homofermentative bacteria, required malt wort for growth, and could not be cultured on normal laboratory media, such as MRS. Their metabolism during the last 20 to 30 h of fermentation was associated with yeast death and autolysis and further accumulation of lactate but no additional acetate.     

Oxygen- and Glucose-Dependent Regulation of Central Carbon Metabolism in Pichia anomala

We investigated the regulation of the central aerobic and hypoxic metabolism of the biocontrol and non-Saccharomyces wine yeast Pichia anomala. In aerobic batch culture, P. anomala grows in the respiratory mode with a high biomass yield (0.59 g [dry weight] of cells g of glucose⁻¹) and marginal ethanol, glycerol, acetate, and ethyl acetate production. Oxygen limitation, but not glucose pulse, induced fermentation with substantial ethanol production and 10-fold-increased ethyl acetate production. Despite low or absent ethanol formation, the activities of pyruvate decarboxylase and alcohol dehydrogenase were high during aerobic growth on glucose or succinate. No activation of these enzyme activities was observed after a glucose pulse. However, after the shift to oxygen limitation, both enzymes were activated threefold. Metabolic flux analysis revealed that the tricarboxylic acid pathway operates as a cycle during aerobic batch culture and as a two-branched pathway under oxygen limitation. Glucose catabolism through the pentose phosphate pathway was lower during oxygen limitation than under aerobic growth. Overall, our results demonstrate that P. anomala exhibits a Pasteur effect and not a Crabtree effect, i.e., oxygen availability, but not glucose concentration, is the main stimulus for the regulation of the central carbon metabolism.     

Comparative metabolic profiling to investigate the contribution of <Emphasis Type="Italic">O. oeni</Emphasis> MLF starter cultures to red wine composition

In this research work we investigated changes in volatile aroma composition associated with four commercial Oenococcus oeni malolactic fermentation (MLF) starter cultures in South African Shiraz and Pinotage red wines. A control wine in which MLF was suppressed was included. The MLF progress was monitored by use of infrared spectroscopy. Gas chromatographic analysis and capillary electrophoresis were used to evaluate the volatile aroma composition and organic acid profiles, respectively. Significant strain-specific variations were observed in the degradation of citric acid and production of lactic acid during MLF. Subsequently, compounds directly and indirectly resulting from citric acid metabolism, namely diacetyl, acetic acid, acetoin, and ethyl lactate, were also affected depending on the bacterial strain used for MLF. Bacterial metabolic activity increased concentrations of the higher alcohols, fatty acids, and total esters, with a larger increase in ethyl esters than in acetate esters. Ethyl lactate, diethyl succinate, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate concentrations were increased by MLF. In contrast, levels of hexyl acetate, isoamyl acetate, 2-phenylethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated. Formation of ethyl butyrate, ethyl propionate, ethyl 2-methylbutryate, and ethyl isovalerate was related to specific bacterial strains used, indicating possible differences in esterase activity. A strain-specific tendency to reduce total aldehyde concentrations was found at the completion of MLF, although further investigation is needed in this regard. This study provided insight into metabolism in O. oeni starter cultures during MLF in red wine.     

Characterization of Kloeckera apiculata strains from the Friuli regionin Northern Italy

Forty-nine strains of Kloeckera apiculata, isolated from the Friuli region in Italy, were differentiated on the basis of fermentation behaviour and production of secondary compounds in two different grape musts at 18 °C. The isolates exhibited a controlled production of acetic acid, only in a few cases more that 1 g/l. In Moscato grape must the strains exhibited a more uniform behaviour for the production of higher alcohols, ethyl acetate and acetoin than in red grapes. In general, higher levels of ethanol, glycerol and acetic acid were produced in red grape must fermentation. Apiculate strains behaved differently in the two musts, with different metabolic phenotypes dominating the fermentation process. The existence of different metabolic phenotypes correlated with the must composition underlines the need to perform a selection of indigenous apiculate yeasts to obtain the desired consistent products.     

Yeast Diversity and Persistence in Botrytis-Affected Wine Fermentations

Culture-dependent and -independent methods were used to examine the yeast diversity present in botrytis-affected (“botrytized”) wine fermentations carried out at high (~30°C) and ambient (~20°C) temperatures. Fermentations at both temperatures possessed similar populations of Saccharomyces, Hanseniaspora, Pichia, Metschnikowia, Kluyveromyces, and Candida species. However, higher populations of non-Saccharomyces yeasts persisted in ambient-temperature fermentations, with Candida and, to a lesser extent, Kluyveromyces species remaining long after the fermentation was dominated by Saccharomyces. In general, denaturing gradient gel electrophoresis profiles of yeast ribosomal DNA or rRNA amplified from the fermentation samples correlated well with the plating data. The direct molecular methods also revealed a Hanseniaspora osmophila population not identified in the plating analysis. rRNA analysis also indicated a large population (>10⁶ cells per ml) of a nonculturable Candida strain in the high-temperature fermentation. Monoculture analysis of the Candida isolate indicated an extreme fructophilic phenotype and correlated with an increased glucose/fructose ratio in fermentations containing higher populations of Candida. Analysis of wine fermentation microbial ecology by using both culture-dependent and -independent methods reveals the complexity of yeast interactions enriched during spontaneous fermentations.