Florian F Bauer

Stellenbosch University | SUN · South African Grape and Wine Research Institute

Fermenting grape juice provides a habitat for a well-mapped and evolutionarily relevant microbial ecosystem consisting of many natural or inoculated strains of yeasts and bacteria. The molecular nature of many of the ecological interactions within this ecosystem remains poorly understood, with the partial exception of interactions of a metabolic na...

Consumers’ mental pictures of wine are multifaceted and are shaped by their sensory (taste, smell, visual, sensation) perceptions, in addition to emotional, cultural and extrinsic (brand, price, and awards) influences. This study explores whether consumers from three different wine cultures share mental representations of three wine concepts. Throu...

Laboratory-based evolution has long been successfully implemented for the generation of desired phenotypes in microbial strain development. The approach also provides insights into evolutionary mechanisms and adaptive molecular strategies which may be too complex to unravel in natural environments. The selection pressure in most of these approaches...

Geographic origin and terroir are very important parameters for wine and significantly impact price. Incorrect declarations are known to occur intentionally to increase profit, thus, measures for control are required. Accompanying paperwork has been shown to be unreliable, thus, control of the product itself is required. Here we investigate and com...

Higher-order interactions are one of the major blind spots in our understanding of microbial ecosystems. These systems remain largely unpredictable and are characterized by nonlinear dynamics, in particular when the system is comprised of more than two entities.

Microbial diversity in vineyards and in grapes has generated significant scientific interest. From a biotechnological perspective, vineyard and grape biodiversity has been shown to impact soil, vine, and grape health and to determine the fermentation microbiome and the final character of wine. Thus, an understanding of the drivers that are responsi...

Wine is characterised by an underlying aromatic volatile profile, which allows human subjects to easily recognise the product as “wine” by smell alone. Yeast metabolism significantly contributes to wine organoleptic properties, and some yeast metabolism-derived compounds contribute to the vinous character of wine. However, the relative contribution...

Lipids are essential energy storage compounds and are the core structural elements of all biological membranes. During wine alcoholic fermentation, the ability of yeasts to adjust the lipid composition of the plasma membrane partly determines their ability to cope with various fermentation-related stresses, including elevated levels of ethanol and...

Microbial multispecies ecosystems are responsible for many biotechnological processes and are particularly important in food production. In wine fermentations, in addition to the natural microbiota, several commercially relevant yeast species may be co-inoculated to achieve specific outcomes. However, such multispecies fermentations remain largely...

Consumers are willing to pay significantly higher prices for food and beverage products of certain, especially valued geographic origin. The control of declared geographic origin of food and beverages thus is an important issue, as it represents protection and prevention of consumer deception and fraud. We compared wine samples from Austria and Sou...

Continuous cell-to-cell contact between different species is a general feature of all natural environments. However, almost all research is conducted on single-species cultures, reflecting a biotechnological bias and problems associated with the complexities of reproducibly growing and controlling multispecies systems. Consequently, biotic stress d...

Anecdotal evidence suggests that spontaneous alcoholic fermentation of grape juice is becoming a more popular option in global wine production. Wines produced from the same grape juice by inoculation or spontaneous fermentation usually present distinct chemical and sensorial profiles. Inoculation has been associated with more similar end-products,...

Culture is an important factor that influences how marketing interacts with food choice. This study aims at exploring the effect of consumers’ Country of Origin (COO) on wine representations and perception using Chenin blanc as a model. The first objective was to evaluate the role of origin in the construction of the representation. We used the the...

Lipids are essential components of all living cells. In an oenological context, the supply of unsaturated lipids in grape juice allows the yeasts to grow and ferment, despite very low levels of oxygen. The current study proposes a systematic optimization procedure for the analysis of fatty acids and sterols relevant to the grape fermentation proces...

The general interest in microbial ecology has skyrocketed over the past decade, driven by technical advances and by the rapidly increasing appreciation of the fundamental services that these ecosystems provide. In biotechnology, ecosystems have many more functionalities than single species, and, if properly understood and harnessed, will be able to...

Lipids are valuable compounds present in all living organisms, which display an array of functions related to compartmentalization, energy storage and enzyme activation. Furthermore, these compounds are an integral part of the plasma membrane which is responsible for maintaining structure, facilitating the transport of solutes in and out of the cel...

The outcome of co- or sequential inoculation of Lachancea thermotolerans in winemaking remains unpredictable due to a lack of integrated data regarding the impact of grape juice composition on L. thermotolerans fermentation behaviour. Here, we investigate the impact of nitrogen composition on fermentation characteristics and aroma compound producti...

Perception of aroma compounds in wine is the result of complex phenomena, in which the compounds, their concentrations, the matrix, and their interactions play a role. In order to evaluate the impact of compounds and matrices on red wine aroma perception, a two‐part study was conducted. First, the work evaluated Projective Mapping (PM) and Descript...

The yeast Lachancea thermotolerans is of significant biotechnological interest, and selected strains of this species have become commonly used starter cultures in wine fermentation. However, the impact of this species on wine is frequently limited by the rapid dominance of Saccharomyces cerevisiae strains which are better adapted to wine alcoholic...

Saccharomyces cerevisiae and Lactobacillus plantarum are responsible for alcoholic and malolactic fermentation, respectively. Successful completion of both fermentations is essential for many styles of wine, and an understanding of how these species interact with each other, as well as the development of compatible pairings of these species, will h...

Ecological interactions between different species of yeasts have been observed and described extensively, but the mechanisms of interaction remain poorly understood. A hindrance to the characterization of multispecies yeast ecosystems is the lack of accurate methods for rapid real-time analysis of population dynamics in synthetic multispecies conso...

Yeast and microalgae are microorganisms with widely diverging physiological and biotechnological properties. Accordingly, their fields of applications diverge: yeasts are primarily applied in processes related to fermentation, while microalgae are used for the production of high-value metabolites and green technologies such as carbon capture. Heter...

Stress is a normal part of life for fungi, which can survive in environments considered inhospitable or hostile for other organisms. Due to the ability of fungi to respond to, survive in, and transform the environment, even under severe stresses, many researchers are exploring the mechanisms that enable fungi to adapt to stress. The International S...

Spontaneous wine fermentation is characterized by yeast population evolution, modulated by complex physical and metabolic interactions amongst various species. The contribution of any given species to the final wine character and aroma will depend on its numerical persistence during the fermentation process. Studies have primarily evaluated the eff...

The qualitative perceptual interactions of single and binary mixtures of four compounds: guaiacol (‘burnt/smoky’), o-cresol (‘phenolic/ tar’), 4-ethylphenol (4-EP, ‘leather/barnyard’), and 2-isobutyl-3- methoxypyrazine (IBMP, ‘green pepper/herbaceous’), were studied in a partially de-aromatised red wine matrix. Using Descriptive Analysis, each comp...

The qualitative sensory perception of individual and of complex mixtures of five compounds, guaiacol ('burnt note'), o-cresol ('phenolic/tar'), 4-EP ('leather/barnyard'), IBMP ('green pepper/herbaceous'), and TCA ('cork taint/ mouldy') were tested in a partially de-aromatised red wine matrix using descriptive analysis by a trained panel of eleven j...

The qualitative sensory perception of individual and of complex mixtures of five compounds, guaiacol (‘burnt note’), o-cresol (‘phenolic/tar’), 4-ethylphenol (4-EP, ‘leather/barnyard’), 2-iso-butyl-3-methoxypyrazine (IBMP, ‘green pepper/herbaceous’), and 2,4,6-trichloroanisole (TCA, ‘cork taint/ mouldy’) were tested in a partially de- aromatised re...

In the macroscopic world, ecological interactions between multiple species of fauna and flora are recognised as major role-players in the evolution of any particular species. By comparison, research on ecological interactions as a driver of evolutionary adaptation in microbial ecosystems has been neglected. The evolutionary history of the budding y...

Factors influencing the olfactory perception of wine include (but are not limited to) the nature and concentration of compounds in the wine, the genetic make-up and experience of the assessor and the specific wine matrix in which the compounds are embedded. As the composition of the solution has been shown to have a profound effect of the release a...

Wine is of great economic and cultural significance for South Africa, but some population groups were until relatively recently denied equal access to wine and alcohol products. The South African wine industry has launched various campaigns in recent years that aimed at portraying wine as an acceptable and attractive choice when alcohol consumption...

In grape must, nitrogen is available as a complex mixture of various compounds (ammonium and amino acids). Wine yeasts assimilate these multiple sources in order to suitably fulfil their anabolic requirements during alcoholic fermentation. Nevertheless, the order of uptake and the intracellular fate of these sources is likely to differ between stra...

[This corrects the article DOI: 10.3389/fbioe.2018.00169.].

Unsaturated fatty acids and sterols are essential constituents of the yeast plasma membrane. Recently, their contribution to modulating the production of yeast-derived volatile compounds has received significant attention. The objective of this study was to determine how sterol and lipid supplementation, including ergosterol, plant sterols or oleic...

Microbial biotechnological processes can be based on single species pure cultures or on multi-species assemblages. While these assemblages can be advantageous by offering more functionalities and more resilience to changing environmental conditions, they can be unpredictable and difficult to control under synthetically engineered growth conditions....

Background In wine fermentation starter cultures, the blending of non-Saccharomyces yeast with Saccharomyces cerevisiae to improve the complexity of wine has become common practice, but data regarding the impact of co-cultivation on yeast physiology and on genetic and metabolic regulation remain limited. Here we describe a transcriptomic analysis o...

Vitis vinifera is one of the most widely planted crops and holds important economic value in South Africa and Austria. Grapes obtained from this plant harbour a complex fungal community which plays a crucial role in the wine fermentation process and influences wine flavour and aroma. For many years the contributions of the natural yeasts has been e...

Unsaturated fatty acids and sterols are essential constituents of the yeast plasma membrane. Recently, their contribution to modulating the production of yeast-derived volatile compounds has received significant attention. The objective of this study was to determine how sterol and lipid supplementation, including ergosterol, plant sterols or oleic...

Malodourous compounds, including volatile phenols (VPs) are frequently found at concentrations below their odour thresholds in wine, and may therefore be considered to present no threat to wine quality. Most investigations into smoke taint quantify compounds by chemical/analytical means, or investigate sensory effects of supra- and peri-threshold c...

Vitis vinifera is one of the most widely planted crops and holds important economic value in South Africa and Austria. Grapes obtained from this plant as well as their derivative must harbour a complex fungal community which plays a crucial role in wine fermentation process as it influences wine flavour and aroma. For many years the contributions o...

Natural alcoholic fermentation is initiated by a diverse population of several non-Saccharomyces yeast species. However, most of the species progressively die off, leaving only a few strongly fermentative species, mainly Saccharomyces cerevisiae. The relative performance of each yeast species is dependent on its fermentation capacity, initial cell...

Protein precipitation, also referred to as protein instability, may lead to haziness in bottled wines and result in significant commercial losses. To avoid problems of this nature, fining finished wines with clay (bentonite) is the most commonly applied methodology. However, bentonite fining reduces yield and may affect wine quality. Protein haze h...

The odor detection threshold (ODT) of a compound is the lowest concentration at which individuals can reliably perceive a difference between a sample and its corresponding control, with 50% performance above chance. Wine is a complex matrix, and ODTs used in studies on wine can be based on inappropriate matrices and informal sensory methodologies....

The impact of direct (physical) versus indirect (metabolic) interactions between different yeast species has attracted significant research interest in recent years. This is due to the growing interest in the use of multispecies consortia in bioprocesses of industrial relevance and the relevance of interspecies interactions in establishing stable s...

Acidity is one of the primary sensory elements in wine, and the balance of sugar and acidity is probably the strongest element affecting wine appreciation. However, little is known about how yeast strains and fermentation conditions will affect the production of fermentation-derived acids, including acetic, succinic and pyruvic acid. This study emp...

Grape sugar conversion to ethanol and carbon dioxide is the primary biochemical reaction in alcoholic wine fermentation, but microbial interactions as well as complex secondary metabolic reactions are equally relevant in terms of the composition of the final wine produced. The chemical composition of a wine determines the taste, flavour and aroma o...

The conversion of grape sugar to ethanol and carbon dioxide is the primary biochemical reaction in alcoholic wine fermentation, but microbial interactions, as well as complex secondary metabolic reactions, are equally relevant in terms of the composition of the final wine produced. The chemical composition of a wine determines the taste, flavour an...

Acidity is one of the primary sensory elements in wine, and the balance of sugar and acidity is probably the strongest element affecting wine appreciation. However, little is known about how yeast strains and fermentation conditions will affect the production of fermentation-derived acids, including acetic, succinic and pyruvic acid. This study emp...

Non-Saccharomyces yeasts impact wine fermentations and can diversify the flavour profiles of wines. However, little information is available on the metabolic networks of most of these species. Here we show that unlike the main wine yeast Saccharomyces cerevisiae, Torulaspora delbrueckii and to a lesser extent Lachancea thermotolerans produce signif...

L-Carnitine is a key metabolite in the energy metabolism of eukaryotic cells, functioning as a shuttling molecule for activated acyl-residues between cellular compartments. In higher eukaryotes this function is essential, and defects in carnitine metabolism has severe effects on fatty acid and carbon metabolism. Carnitine supplementation has been a...

Protein haze formation in bottled wines is a significant concern for the global wine industry, and wine clarification before bottling is therefore a common but expensive practice. Previous studies have shown that wine yeast strains can reduce haze formation through the secretion of certain mannoproteins, but it has been suggested that other yeast-d...

Confirmation of OT levels for guaiacol, o-cresol, 4-ethyphenol, iBMP, and TCA in a partially dearomatised red wine base

The preprint provides valuable information regarding the manner in which initial must parameters and environmental conditions throughout fermentation may affect wine acidity.It also provides important background information for oenological strategies which aim to optimise the acid balance of wines.

This review will summarizes the current knowledge about the origin, synthesis and analysis of organic acids in wine, as well as on the management of wine acidity.

The data shows how different fermentation temperature affects glucose/fructose utilisation (A) and ethanol production (B) of five commercial yeast strains

The data shows how different initial pH of the must affects on glucose/fructose utilisation (A) and ethanol production (B) of five commercial yeast strains

The data shows how different initial must sugar contents affects on glucose/fructose utilisation (A) and ethanol production (B) of five commercial yeast strains

The increasingly large volumes of publicly available sensory descriptions of wine raises the question whether this source of data can be mined to extract meaningful domain-specific information about the sensory properties of wine. We introduce a novel application of formal concept lattices, in combination with traditional statistical tests, to visu...

Under industrial conditions, fermenting juice is normally not mechanically agitated; thermodynamic forces will lead to some rotating motion of the medium. At laboratory scale, research aims to mimic industrial conditions using a standardised synthetic grape juice-like medium. The level of agitation applied, however, to fermentations differs between...

Oxygen is sometimes deliberately introduced in winemaking at various stages to enhance yeast biomass formation and prevent stuck fermentation. However, there is limited information on how such interventions affect the dynamics of yeast populations. Our previous study in synthetic grape juice showed that oxygen supply enhances the persistence of Lac...

Nitrogen availability and utilization by Saccharomyces cerevisiae significantly influence fermentation kinetics and the production of volatile compounds important for wine aroma. Amino acids are the most important nitrogen source and have been classified based on how well they support growth. This study evaluated the effect of single amino acids on...