# Aroma Profile of Monovarietal _Pet-Nat_ Ciders: The Role of Croatian Traditional Apple Varieties
## 1 Introduction
Considering that autolysis of yeasts takes place during maturation on lees, the sensory and foaming properties of the cider are significantly modified [17; 18]. As part of the general trend toward natural wines, sparkling ciders can be obtained by _Methode Ancestrale_ or _Petillant Naturel_ (_Pet-Nat_) as one of the oldest methods of natural sparkling wine production. _Pet-Nat_ involves authentic craftsmanship, with production in mostly small quantities, and the natural handling of wine. In _Pet-Nat_ production, the natural (spontaneous) fermentation driven by indigenous flora present on apples, equipment, and in the cell, is interrupted as the wine is moved from a vat into individual bottles while it is still fermenting, and then sealed under a crown cap. The traditional production of cider in France is characterized by spontaneous fermentation with indigenous microorganisms, and bottling when its density is between 1.009 and 1.029, depending on the desired level of sweetness, and ADY can be added before bottling to obtain sparkling cider [19]. Modification of this method can be achieved by finishing the fermentation in isobaric tank and bottling of sparkling cider after ageing on the lees, an isobaric filler. _Pet-Nat_ ciders are usually completely fermented and dry, and the pressure in the bottle is usually 2.5-3 bar. _Petillant naturel_ wines are commonly unfiltered, which leaves them cloudy, with some lees sediment at the bottom of the bottle. The sensory profile of _Pet-Nat_ ciders is significantly associated with raw material, production parameters and microbial activity [19]. Cider microbiota are strongly influenced by variety, and picking apples from the ground brings more bacterial diversity [20]. Dueto the variations in the proportions of a'resident' and 'transitory' microflora the cider yeast population fluctuates from vintage to vintage [21]. The microbial ecology of ciders is complex, and includes several genera, species and strains of yeasts and bacteria [22; 23]. Yeast diversity is higher in cider musts than in bottled ciders and among many species [24], the main yeasts found in cider are _Saccharomyces_ yeasts [19; 25]. According to [PERSON] et al. [24] and [PERSON] et al. [26], in French and Spanish ciders, _Saccharomyces_ is the predominant species from the beginning to the middle steps of the fermentation process, whereas _Saccharomyces cerevisiae_ takes over the process in the final stages of fermentation. The cider-making process typically involves three main stages: apple crushing and pressing out the juice, followed by the most important stage of elaboration, fermentation. This includes the classical alcoholic fermentation of sugars into ethanol performed by yeast strains and malotactic fermentation (MLF), and processed by lactic acid bacteria (LAB) that can occur during the maturation [19]. In the late 1980s, modern ciders were born: ciders containing juice and flavorings began to be produced, alongside traditional ciders. The industry calls these 'flavored ciders', and they can contain ingredients such as juice of other fruits, extracts, flavorings, etc. [2]. Since trends over the last few years have resulted in diverse, natural, and locally produced beverages, cider reappeared in a food markets, restaurants and bars [6] as a fermented beverage, for which the recognition of _terroir_ is important for appreciation [19]. With increased cider consumption, cider makers were looking for ways to diversify their products. The newest trend in cider production is natural craft ciders, using whole juice from local apple varieties without any addition of preservatives, sugar, or active dry yeast (ADY) to distinguish them from industrial ciders made from concentrate, water, and additives. In addition to the varietal choice and maturity of the apples [27], the cider typicity is significantly associated with microbial activities and indigenous microorganisms [7; 12; 14].