## 1 Introduction
Historically linked with spontaneous fermentation processes, such as in the production of lambic beers, these wild yeasts are now being explored for their ability to diversify flavours and aromas in fermented products, thereby enhancing their organoleptic qualities [11; 12]. However, research and applications in this area remain quite limited. In contrast to baker's yeast, many non-_Saccharomyces_ yeast strains have been reported to metabolise various types of carbohydrates. _Kluyveromyces lactis_, for example, utilises lactose. [PERSON] and coworkers highlighted the ability _of Yarrowia lipolytica_ and _Candida maltose_ to assimilate hydrocarbons, fatty acids, and lipids [13]. Pentoses such as xylose and arabinose can also be assimilated by certain yeast strains, for instance, _Pichia stipits_ and _Candida shelatate_[14]. Some non-_Saccharomyces_ yeasts present the abilities to utilise more complex carbon sources than _S. cerevisiae_ and to survive in harsher conditions [15]. There is growing awareness of the advantages of conducting bioprocesses at a reduced temperature. Low-temperature fermentation in industrial processes is typically defined within the range of 10-18 \({}^{\circ}\)C for fruit-based fermentations. In contrast, high-temperature fermentation is carried out at the temperature above 25 \({}^{\circ}\)C, which is close to the optimal temperature for yeast activity [16; 17; 18]. Using lower temperatures offers a great number of benefits, including achieving energy savings by eliminating the need to use additional heat during the process, thus reducing costs [19]. At low temperatures, slower microbial metabolism leads to more controlled fermentation, reducing unwanted reactions and by-products like volatile acidity, higher alcohols, and aldehydes while preserving the balance of acids and aroma compounds [20; 21]. Microorganisms adapted to low temperatures exhibit high growth rates, enzymatic activity, and catalytic efficiency at temperatures much lower than their mesophilic counterparts. Thus, their use can reduce the risk of microbial contamination [22]. Furthermore, the fermentation process not only leads to the formation of specific products with unique flavour and aroma characteristics but is also utilised in the production of natural food additives, probiotics, and functional foods. Incorporating microorganisms in fermentation results in a final product that offers many health benefits for humans [23]. A particularly desirable group of compounds which can be formed successfully by yeasts are volatile organic compounds (VOCs). These compounds are characterised by a low molecular weight and usually present a distinctive odour. They are generally produced by microorganisms during the fermentation process as by-products of carbon metabolism [24; 25]. In the natural environment, VOCs produced by yeast serve multiple purposes, including for communication between cells and as a defence mechanism [26]. Certain yeast strains, such as _Wickerhamomyces anomulus_, _Metschnikowia pulcherrima_, _Aurebosidium pullulans_, and _Saccharomyces cerevisiae_, produce VOCs that can potentially suppress the growth and development of pathogens [27]. In industry, they can contribute to the sensory profiles of fermented products. The production of volatiles by yeast has attracted great interest, especially due to its potential to enrich the diversity of aromas in fermented foods and beverages. The production of volatile compounds is connected to the parameters of the fermentation process, the composition of the medium, the pH, temperature, and strain selection. Thus, the amount and profile of VOCs produced by yeast can differ from species to species [26]. The most abundant VOCs are typically esters, alcohols, acids, aldehydes, ketones, and lactones, as well as sulphur and nitrogen compounds [25]. Apple pomace was selected as a raw material because Poland is one of the leading apple producers in the world. During the processing of apples, enormous amounts of waste biomass are generated.