Nuruk is the cornerstone of traditional Korean alcohol production. This naturally fermented starter cake, typically made from wheat or rice and allowed to colonize with a diverse community of molds, yeasts, and bacteria, supplies the enzymes that break down starches in grains into fermentable sugars. Because nuruk is produced through spontaneous microbial growth, mashes made with it contain a rich and variable cocktail of microorganisms, which in turn generates a wide spectrum of flavor precursors. When such a mash is distilled, the volatile compounds formed during fermentation, including esters, higher alcohols, organic acids, and aldehydes, are carried into the distillate and define the spirit’s aroma. This makes the fermentation stage, and especially the yeast population within it, a decisive lever for controlling the sensory quality of the final product.

In the new study, Son set out to test whether commercially available wild yeasts could act as that lever in a controlled and reproducible way. The experimental design compared three commercial non-Saccharomyces yeasts, Lachancea thermotolerans, Metschnikowia pulcherrima, and Torulaspora delbrueckii, with a mixed-yeast preparation combining Saccharomyces cerevisiae and Torulaspora delbrueckii, and with a standard brewing yeast. A control fermentation relying on the native microbes of the nuruk mash completed the set. After fermentation, all of the mashes were processed under identical conditions using vacuum distillation, a technique that lowers the boiling point of ethanol and volatile aroma compounds, allowing them to be collected at gentler temperatures and helping to preserve delicate aromatic molecules that might otherwise be degraded or lost.

The analytical work focused on three complementary layers of the spirits’ chemistry. First, basic physicochemical properties such as alcohol content were measured to assess how efficiently each yeast converted sugars into ethanol. Second, the organic acid composition of the distillates was profiled, since organic acids contribute sourness, complexity, and important ester-forming precursors. Third, the relative abundances of volatile aroma compounds were compared, capturing the esters, higher alcohols, and other molecules that dominate the human perception of flavor in distilled spirits. Together, these measurements allowed the study to map how each microbial strategy translated into a distinct chemical signature in the glass.

One of the most striking results concerned fermentation performance. Among all the inoculated yeasts, Lachancea thermotolerans produced the highest alcohol content in the main distillate before the standard adjustment step that brings commercial soju to its final bottling strength. This finding aligns with the growing reputation of L. thermotolerans in the beverage industry, where it is increasingly valued for its robust fermentative capacity and its ability to modulate acidity. In the context of distilled soju, a yeast that reliably pushes ethanol yields higher could offer distillers both economic and quality advantages, since fermentation efficiency directly affects the quantity and character of the raw spirit collected.

Paradoxically, the control fermentation, which relied entirely on the microbes naturally present in the nuruk mash, produced the highest relative abundances of total esters and of ethyl acetate, one of the most abundant and influential aroma compounds in distilled spirits. Ethyl acetate contributes fruity, slightly solvent-like notes at moderate concentrations, and its prominence in the control sample suggests that the spontaneous microbial community of nuruk remains a powerful engine of ester formation. This result underscores a central tension in modern traditional-spirit production: wild, uncontrolled fermentation can generate exceptional aromatic richness, but it does so at the cost of consistency, which is precisely what commercial starter cultures are meant to provide.

The mixed-yeast preparation combining Saccharomyces cerevisiae with Torulaspora delbrueckii emerged as perhaps the most distinctive profile in the study. This co-inoculation produced the highest total organic acid content of any treatment, along with elevated relative abundances of total higher alcohols and isoamyl alcohol, a compound associated with malty, banana-like notes. At the same time, the mixed culture yielded only a very weak furfural signal. Furfural, which forms from heat-induced degradation of sugars during distillation, contributes almond-like and caramelized nuances but can also impart harshness at higher levels. A very low furfural signal, combined with enriched organic acids and higher alcohols, suggests that the mixed-yeast approach could produce a rounder, fuller-bodied spirit with fewer sharp edges, offering distillers a way to engineer complexity without relying on uncontrolled fermentation.

Metschnikowia pulcherrima, another of the wild yeasts tested, left its own unmistakable mark on the distillate. Spirits fermented with this organism showed relatively high signals for isoamyl acetate, the ester responsible for banana-like aromas, along with ethyl lactate, which contributes creamy and fruity nuances, and 2-phenylethanol, a rose-scented higher alcohol highly prized in both wine and spirits. This trio of compounds points toward a floral, fruity, and soft aromatic profile, consistent with the growing use of M. pulcherrima as a co-fermenter in winemaking, where it is known to enhance aroma intensity and freshness. Its performance in a distilled soju context demonstrates that the aromatic talents of this yeast survive the distillation process and can be transferred to spirits, not just to wine.

Taken together, the results deliver a clear message: yeast selection is not a minor technical detail in soju production but a primary determinant of the spirit’s chemical identity. Each of the tested yeasts produced a measurably different profile of alcohols, acids, esters, and aroma-active compounds, meaning that distillers can, in principle, choose a starter culture the way a perfumer chooses an ingredient, steering the final product toward fruitiness, fullness, floral character, or clean neutrality. The use of commercially available wild yeasts also offers a middle path between the unpredictability of spontaneous nuruk fermentation and the uniformity of a single brewing strain, preserving some of the aromatic richness of tradition while adding a measure of reproducibility that modern markets demand.

The study also situates Korean soju within a global research trend. Non-Saccharomyces yeasts such as Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowia pulcherrima have been the subject of intense investigation in wine, beer, and other fermented foods over the past decade, with researchers documenting their roles in modulating acidity, releasing bound aroma compounds, and reducing undesirable byproducts. Applying these organisms to a traditional Asian distilled spirit made from nuruk mash represents a meaningful extension of that work, bridging old-world fermentation practices and new-world microbial technology. As consumer interest in craft spirits and terroir-driven flavors continues to grow, the ability to tune the aroma of distilled soju through deliberate yeast selection could open new categories of premium products, giving one of Korea’s oldest drinks a scientifically engineered future without abandoning the microbial heritage at its core.

Subject of Research: Effects of commercial wild yeasts on the chemical and aroma profiles of Korean distilled soju produced from nuruk mash

Article Title: Effects of commercial wild yeasts on the chemical and aroma profiles of Korean distilled soju produced from nuruk mash

Article References: Son, E.-S. (2026). Effects of commercial wild yeasts on the chemical and aroma profiles of Korean distilled soju produced from nuruk mash. Food Science and Biotechnology. https://doi.org/10.1007/s10068-026-02294-7

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02294-7

Keywords: distilled soju, nuruk mash, non-Saccharomyces yeasts, Lachancea thermotolerans, Metschnikowia pulcherrima, Torulaspora delbrueckii, Saccharomyces cerevisiae, aroma compounds, organic acids, vacuum distillation, Korean traditional alcohol, fermentation