As a metaphor, lemons get a bad rap; however the proverb ‘if life gives you lemons, make lemonade’ is often used in a motivational context. The same could be said of Hanseniaspora in winemaking. Despite its predominance in vineyards and grape must, this lemon-shaped yeast is underappreciated in terms of its contribution to the overall sensory profile of fine wine. Species belonging to this apiculate yeast are known for being common isolates not just on grape berries, but on many other fruits. They play a critical role in the early stages of a fermentation and can influence the quality of the final product. Their deliberate addition within mixed-culture fermentations shows promise in adding to the complexity of a wine and thus provide sensorial benefits. Hanseniaspora species are also key participants in the fermentations of a variety of other foodstuffs ranging from chocolate to apple cider. Outside of their role in fermentation, Hanseniaspora species have attractive biotechnological possibilities as revealed through studies on biocontrol potential, use as a whole-cell biocatalyst and important interactions with Drosophila flies. The growing amount of ‘omics data on Hanseniaspora is revealing interesting features of the genus that sets it apart from the other Ascomycetes. This review collates the fields of research conducted on this apiculate yeast genus.

Apiculate yeasts belonging to the genus Hanseniaspora are commonly isolated from viticultural settings and often dominate the initial stages of grape must fermentations. Although considered spoilage yeasts, they are now increasingly becoming the focus of research, with several whole-genome sequencing studies published in recent years. However, tools for their molecular genetic manipulation are still lacking. Here, we report the development of a tool for the genetic modification of Hanseniaspora uvarum. This was employed for the disruption of the HuATF1 gene, which encodes a putative alcohol acetyltransferase involved in acetate ester formation. We generated a synthetic marker gene consisting of the HuTEF1 promoter controlling a hygromycin resistance open reading frame (ORF). This new marker gene was used in disruption cassettes containing long-flanking (1000 bp) homology regions to the target locus. By increasing the antibiotic concentration, transformants were obtained in which both alleles of the putative HuATF1 gene were deleted in a diploid H. uvarum strain. Phenotypic characterisation including fermentation in Müller-Thurgau must showed that the null mutant produced significantly less acetate ester, particularly ethyl acetate. This study marks the first steps in the development of gene modification tools and paves the road for functional gene analyses of this yeast.

In this study, the aroma-production profiles of seven different Hanseniaspora strains, namely H. guilliermondii, H. meyeri, H. nectarophila, H. occidentalis, H. opuntiae, H. osmophila and H. uvarum were determined in a simultaneous co-inoculation with the wine yeast Saccharomyces cerevisiae Champagne Epernay Geisenheim (Uvaferm CEG). All co-inoculated fermentations with Hanseniaspora showed a dramatic increase in ethyl acetate levels except the two (H. occidentalis and H. osmophila) that belong to the so-called slow-evolving clade, which had no meaningful difference, compared to the S. cerevisiae control. Other striking observations were the almost complete depletion of lactic acid in mixed-culture fermentations with H. osmophila, the more than 3.7 mg/L production of isoamyl acetate with H. guilliermondii, the significantly lower levels of glycerol with H. occidentalis and the increase in certain terpenols, such as citronellol with H. opuntiae. This work allows for the direct comparison of wines made with different Hanseniapora spp. showcasing their oenological potential, including two (H. meyeri and H. nectarophila) previously unexplored in winemaking experiments.

Non-Saccharomyces yeasts are prevalent at the onset of grape must fermentations and can have a significant influence on the final wine product. In contrast to Saccharomyces cerevisiae, the biosynthetic pathways leading to aroma compound formation in these non-conventional yeasts, in particular those that are derived from amino acid metabolism, remains largely unexplored. Within a synthetic must environment, we investigated the amino acid utilization of four species (Hanseniaspora uvarum, Hanseniaspora osmophila, Zygosaccharomyces rouxii, Starmerella bacillaris) and S. cerevisiae. We report on the differential uptake preferences for amino acids with H. uvarum displaying the most rapid uptake of most amino acids. To investigate the fate of amino acids and their direct contribution to aroma synthesis in H. uvarum, H. osmophila and Z. rouxii, musts were supplemented with single amino acids. Aroma profiling undertaken after three days showed the synthesis of specific aroma compounds by the respective yeast was dependent on the specific amino acid supplementation. H. osmophila showed similarities to S. cerevisiae in both amino acid uptake and the synthesis of aroma compounds depending on the nitrogen sources. This study shows how the uptake of specific amino acids contributes to the synthesis of aroma compounds in wine fermentations using different non-Saccharomyces yeasts.

Climate change is altering grape composition and ripening patterns, thereby influencing the selection criteria for wine yeast strains adapted to warmer conditions and fluctuating sugar–acid balances. Previously, we sequenced and annotated the Champagne–Epernay–Geisenheim white wine yeast CEG. CEG is a hybrid tetraploid strain with more than three genome equivalents of Saccharomyces cerevisiae and only 1/3 of a S. kudriavzevii genome. To address climate change issues, we used the limited sporulation capacity of CEG to isolate meiotic progeny. The obtained spore clones were subjected to targeted selection procedures, identifying progeny with enhanced fermentation performance under higher temperature conditions. Spore clones were also selected to carry the FOT4 allele encoding a Fungal Oligopeptide Transporter gene. We identified suitable strains, particularly GYBC 1467, that surpassed the parental strain at 25 °C with enhanced volatile aroma production. Genome sequencing of three spore clones indicated differential loss of S. kudriavzevii DNA. This approach demonstrates that, via a single round meiosis, spore clone isolates with substantially improved fermentation performance compared with the parental strain can be obtained. This provides a fast route for the generation of resilient wine yeasts capable of maintaining wine quality in increasingly difficult fermentation environments.

This study investigates the breeding of the German wine yeast Oppenheimer Kreuz 1894, which carries a FOT1 allele of a fungal oligopeptide transporter, with Freya, a Kveik ale yeast, to enhance fermentation performance and aroma in beer and wine. By combining Kveik traits (osmotolerance, thermotolerance, and rapid fermentation kinetics) with those of a German wine yeast (ethanol tolerance, broadened nitrogen utilization, and aroma production) and introducing FOT1 into an ale background via classical breeding, we aimed to leverage the Saccharomyces biodiversity to improve fermentation activity and expand aromatic complexity. Fermentation products and volatile aroma compounds were quantified by HPLC and HS-SPME-GC-MS. Spore clone derivatives of initial hybrid strains (F₂-generation) showed improved fermentation profiles with increased CO₂ production. In wine fermentations, the best-performing spore clone, GYBC 901, yielded a rich aromatic profile with elevated fruity and floral notes. In beer fermentations, GYBC 899 produced the most diverse and complex aroma. FOT1 was of minor relevance to the breeding outcome, whereas meiotic recombination generated a set of diverse spore clones. These results highlight the potential of strategic yeast breeding to optimize fermentation processes and tailor flavor profiles to diverse product targets. Future work will elucidate metabolic pathways underlying these phenotypes and advance the development of application-specific strains, offering avenues to enhance beverage quality and product differentiation in the fermentation industry.