# _Forentation_
## 1 Introduction  
Cider, an alcoholic beverage produced through the fermentation of apple juice, has experienced a significant rise in popularity within the alcoholic beverage market. Traditional cider-producing and consuming countries such as Spain, England, France, and Ireland have increased the production and consumption of this beverage. Additionally, cider has expanded into new markets, including the United States, Australia, and Asia [1]. In Argentina, cider production is primarily concentrated in the North Patagonian region,where most apple orchards are located. Reflecting global trends, this industry is becoming an increasingly important segment of the apple fruit sector, partly due to the decline in fresh apple exports and the consequent reduction in fresh fruit prices [2]. Unlike in other countries, Argentina does not use apple varieties specifically cultivated for cider-making. Instead, cider production has traditionally relied on apple varieties primarily intended for fresh consumption. In most cases, discarded apples that fail to meet the quality standards required for the fresh fruit market, such as size and color (mainly visual defects), are utilized [3]. Regarding the yeasts used in this industry, spontaneous fermentations or conducted fermentations using commercial cultures are employed. Given the global growth of the cider market, there has been an increasing demand for new yeast strains capable of producing ciders with novel properties. This demand is particularly relevant for Argentine producers, who often rely on foreign yeast starters to ferment apple musts due to the limited local availability of starter cultures. The most commonly used commercial cultures include imported _S. cerevisiae_ strains selected for wine (e.g., ZymafloreTM Spark, Laffort) or cider (e.g., SaFciderTM AC-4, Fermentis) (personal communication). In recent years, research in Argentina has focused on evaluating alternative apple varieties and developing new local yeast strains, aiming to differentiate the product and increase its economic value [4; 5; 6]. An increasingly common strategy to enhance the flavor complexity of ciders is the inoculation of apple musts with pure cultures of yeasts belonging to _Saccharomyces_ genus selected according to their metabolic and technological abilities [7; 8]. More recently, different non-_Saccharomyces_ yeast strains were also evaluated because of their ability to produce specific cider volatile compounds [8; 9; 10; 11; 12]. In a few cases, mixed cultures of two non-_Saccharomyces_ strains [13] or a combination of _S. cerevisiae_ and a non-_Saccharomyces_ yeast were also proposed [14; 15; 16]. Among non-_Saccharomyces_ yeast species, _Pichia kudriazevii_ has gained attention. This species is recognized for its ability to degrade organic acids, release hydrolases and flavor compounds, and exhibit probiotic properties, making it a promising starter culture in the beverage industry [16]. While it is commonly associated with wine due to its prevalence in vineyards and wineries, it has also been isolated from other substrates such as apple surfaces, spontaneous cider and Baijiu fermentations, and sourdough in recent years [6; 15; 17; 18]. Strains of _P. kudriazevii_ have been reported to enhance the aromatic profiles of wines [19; 20; 21] and also contribute to the production of high-quality ciders when used in mixed cultures [14; 15]. The ability of _P. kudriazevii_ to degrade malic acid in wine [22; 23; 24; 25] makes it a promising species for the production of cider from musts with a high concentration of this particularly pungent organic acid. L(-)Malic acid is the predominant component of the non-volatile organic acid fraction in apples. Its concentration is influenced by apple variety, maturity, and climatic conditions. Apples grown in cooler regions tend to have higher levels of L(-)malic acid due to a lower respiratory quotient compared to those from warmer areas [26].