and the Concept of Friendly Yeasts to Increase Autochthonous Wine Flavor Diversity.

In this perspective, we will explain the concept of "friendly" yeasts for developing wine starters that do not suppress desirable native microbial flora at the initial steps of fermentation, as what usually happens with strains. Some non- strains might allow the development of yeast consortia with the native terroir microflora of grapes and its region. The positive contribution of non- yeasts was underestimated for decades.

Systems-based approaches enable identification of gene targets which improve the flavour profile of low-ethanol wine yeast strains.

Metabolic engineering has been vital to the development of industrial microbes such as the yeast Saccharomyces cerevisiae. However, sequential rounds of modification are often needed to achieve particular industrial design targets. Systems biology approaches can aid in identifying genetic targets for modification through providing an integrated view of cellular physiology.

Impact of Australian Dekkera bruxellensis strains grown under oxygen-limited conditions on model wine composition and aroma.

Spoilage of red wine by the yeast species Dekkera bruxellensis is a common problem for the global wine industry. When conditions are conducive for growth of these yeasts in wine, they efficiently convert non-volatile hydroxycinnamic acids into aroma-active ethylphenols, thereby reducing the quality of the wine. It has been demonstrated previously that dissolved oxygen is a key factor which stimulates D.

Effects of rehydration nutrients on H2S metabolism and formation of volatile sulfur compounds by the wine yeast VL3.

In winemaking, nutrient supplementation is a common practice for optimising fermentation and producing quality wine. Nutritionally suboptimal grape juices are often enriched with nutrients in order to manipulate the production of yeast aroma compounds. Nutrients are also added to active dry yeast (ADY) rehydration media to enhance subsequent fermentation performance.

Comparison of inorganic and organic nitrogen supplementation of grape juice - Effect on volatile composition and aroma profile of a Chardonnay wine fermented with Saccharomyces cerevisiae yeast.

Inorganic nitrogen salts, and to a growing extent organic nitrogen preparations, are widely used to ameliorate a nitrogen deficiency in wine fermentation, but the impact of nitrogen supplementation on perceived wine sensory profile is essentially unknown. Supplementation of a low nitrogen Chardonnay grape juice with either ammonium nitrogen or combined amino acid and ammonium nitrogen showed that the type of nitrogen and concentration in the range 160-480mgN/l had a substantial impact on the formation of yeast volatile compounds and perceived wine aroma. Addition of amino acid and ammonium nitrogen increased both acetate and medium chain fatty acid esters to a greater extent and decreased higher alcohols to a lesser extent than ammonium nitrogen alone whereas ammonium nitrogen substantially increased ethyl acetate and acetic acid.

Impacts of variations in elemental nutrient concentration of Chardonnay musts on Saccharomyces cerevisiae fermentation kinetics and wine composition.

Chardonnay, being the predominant white wine-grape cultivar in the Australian wine sector, is subject to widely varying winemaking processes with the aim of producing a variety of wine styles. Therefore, juice composition might not always be ideal for optimal fermentation outcomes. Our aim was to better understand the composition of Chardonnay juice and how compositional parameters impact on fermentation outcomes.

Volatile composition and sensory properties of Shiraz wines as affected by nitrogen supplementation and yeast species: rationalizing nitrogen modulation of wine aroma.

The effects of yeast assimilable nitrogen (YAN) supplementation on Shiraz volatile composition and sensory properties have been investigated. A low YAN Shiraz must (YAN 100 mg/L) was supplemented with nitrogen in the form of diammonium phosphate (DAP) to a final YAN of either 250 or 400 mg/L. Fermentation was carried out with either Saccharomyces cerevisiae or Saccharomyces bayanus , with maceration on skins.

Occurrence of hydrogen sulfide in wine and in fermentation: influence of yeast strain and supplementation of yeast available nitrogen.

Hydrogen sulfide (H₂S) is a powerful aroma compound largely produced by yeast during fermentation. Its occurrence in wines and other fermented beverages has been associated with off-odors described as rotten egg and/or sewage. While the formation of hydrogen sulfide (H₂S) during fermentation has been extensively studied, it is the final H₂S content of wine that is actually linked to potential off-odors.

Comparison of three methods for accurate quantification of hydrogen sulfide during fermentation.

Two analytical approaches for the rapid measurement of hydrogen sulfide (H(2)S) have been compared to a reference method for their potential application as a rapid procedure for the quantification of H(2)S formed during alcoholic fermentations. In one case, silver nitrate, lead acetate, and mercuric chloride selective detector tubes for the analysis of H(2)S in air were investigated. In the other case, a commercially available kit for the diagnosis of nitrogen starvation in wine fermentations, which is based on the detection of H(2)S, was investigated.

Effect of nitrogen supplementation and Saccharomyces species on hydrogen sulfide and other volatile sulfur compounds in shiraz fermentation and wine.

A Shiraz must with low yeast assimilable nitrogen (YAN) was supplemented with two increasing concentrations of diammonium phosphate (DAP) and fermented with one Saccharomyces cerevisiae and one Saccharomyces bayanus strain, with maceration on grape skins. Hydrogen sulfide (H(2)S) was monitored throughout fermentation, and a total of 16 volatile sulfur compounds (VSCs) were quantified in the finished wines. For the S.

Volatile and color composition of young and model-aged Shiraz wines as affected by diammonium phosphate supplementation before alcoholic fermentation.

A Shiraz must with low yeast assimilable nitrogen (YAN) was supplemented with two concentrations of diammonium phosphate (DAP) and then fermented with maceration on grape skins. The nonvolatile, volatile, and color composition of the final wines were investigated. Ethanol and residual sugars were not affected by DAP supplementation, while glycerol, SO 2, and residual YAN increased and acetic acid decreased.

Production of fermentation aroma compounds by Saccharomyces cerevisiae wine yeasts: effects of yeast assimilable nitrogen on two model strains.

The contribution of yeast fermentation metabolites to the aromatic profile of wine is well documented; however, the biotechnological application of this knowledge, apart from strain selection, is still rather limited and often contradictory. Understanding and modeling the relationship between nutrient availability and the production of desirable aroma compounds by different strains must be one of the main objectives in the selection of industrial yeasts for the beverage and food industry. In order to overcome the variability in the composition of grape juices, we have used a chemically defined model medium for studying yeast physiological behavior and metabolite production in response to nitrogen supplementation so as to identify an appropriate yeast assimilable nitrogen level for strain differentiation.

Acetic acid bacteria spoilage of bottled red wine -- a review.

Acetic acid bacteria (AAB) are ubiquitous organisms that are well adapted to sugar and ethanol rich environments. This family of Gram-positive bacteria are well known for their ability to produce acetic acid, the main constituent in vinegar. The oxidation of ethanol through acetaldehyde to acetic acid is well understood and characterised.

The role of lysine amino nitrogen in the biosynthesis of mousy off-flavor compounds by Dekkera anomala.

Mousy off-flavor is an insidious and economically disastrous microbiologically derived spoilage characteristic of wine and other fermented beverages. Tainted wines are rendered unpalatable and there is currently no satisfactory procedure for removal of the off-flavor. Here we report the confirmation of that both d- and l-lysine can act as a precursor for the formation of mousy off-flavor N-heterocycles.

Genetic diversity of Dekkera bruxellensis yeasts isolated from Australian wineries.

Yeasts of the genus Dekkera and its anamorph Brettanomyces represent a significant spoilage issue for the global wine industry. Despite this, there is limited knowledge of genetic diversity and strain distribution within wine and winery-related environments. In this study, amplified fragment length polymorphism (AFLP) analysis was conducted on 244 Dekkera bruxellensis isolates from red wine made in 31 winemaking regions of Australia.

Hydrolysis and transformation of grape glycosidically bound volatile compounds during fermentation with three Saccharomyces yeast strains.

The ability of three Saccharomyces wine yeasts (S. cerevisiae AWRI 838, S. cerevisiae AWRI 1537, and S.

Metabolic profiling as a tool for revealing Saccharomyces interactions during wine fermentation.

The multi-yeast strain composition of wine fermentations has been well established. However, the effect of multiple strains of Saccharomyces spp. on wine flavour is unknown.

De novo synthesis of monoterpenes by Saccharomyces cerevisiae wine yeasts.

This paper reports the production of monoterpenes, which elicit a floral aroma in wine, by strains of the yeast Saccharomyces cerevisiae. Terpenes, which are typical components of the essential oils of flowers and fruits, are also present as free and glycosylated conjugates amongst the secondary metabolites of certain wine grape varieties of Vitis vinifera. Hence, when these compounds are present in wine they are considered to originate from grape and not fermentation.

The 'buttery' attribute of wine--diacetyl--desirability, spoilage and beyond.

The diketone, diacetyl, is a major flavour metabolite produced by lactic acid bacteria (LAB). Of the LAB associated with wine, Oenococcus oeni is encouraged during the malolactic (ML) fermentation, a biodeacidification of wine during which the metabolism of diacetyl occurs. Diacetyl, which imparts a buttery aroma and flavour to many fermented foods and beverages, is a key flavour compound of most fermented dairy products.

Mousy off-flavor of wine: precursors and biosynthesis of the causative N-heterocycles 2-ethyltetrahydropyridine, 2-acetyltetrahydropyridine, and 2-acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176.

The N-heterocyclic bases, 2-ethyltetrahydropyridine (1), 2-acetyl-1-pyrroline (2), and 2-acetyltetrahydropyridine (3) are associated with the occurrence of mousy off-flavor in wine. The biosynthesis of these N-heterocycles by the wine lactic acid bacterium, Lactobacillus hilgardii DSM 20176, was studied by high-cell-density incubation in combination with a minimal chemically defined N-heterocycle assay medium. The key components of the defined N-heterocycle assay medium included D-fructose, ethanol, L-lysine, L-ornithine, and mineral salts.

Decreasing acetic acid accumulation by a glycerol overproducing strain of Saccharomyces cerevisiae by deleting the ALD6 aldehyde dehydrogenase gene.

Glycerol is a major fermentation product of Saccharomyces cerevisiae that contributes to the sensory character of wine. Diverting sugar to glycerol overproduction and away from ethanol production by overexpressing the glycerol 3-phosphate dehydrogenase gene,GPD2, caused S. cerevisiae to produce more than twice as much acetic acid as the wild-type strain (S288C background) in anaerobic cell culture.