# Aroma Profile of Monovarietal _Pet-Nat_ Ciders: The Role of Croatian Traditional Apple Varieties
## 1 Introduction  
The consumption and production of cider, a fermented beverage made from modern and traditional apple varieties (_Malus domestica_ Borkh. ), is an important part of the global market which together with other fruit wines have the fastest growing rates among all alcoholic beverages despite of a decline in total alcoholic beverages revenue growth [1, 2]. According to Fior Markets [3] ciders make less than 1% of the total alcoholic beverages market with global sales estimated at $4.34 billion in 2018 and projected rising to $5.43 billion by 2026. Cider, or apple wine, is low-alcoholic beverage abundant with nutrients [4] that is encountered in many countries around the world, especially in those without agro-climatic conditions required for grapevine cultivation. The impressive statistics, together with the high yield and plentiful varieties of apples in the world make it a very promising segment of the fruit industry [5, 6]. According to The European Cider and Fruit Wine Association (AICV) [2] ciders and sparkling ciders are still predominantly European. Within Europe, the main cider-making countries based largely on farmhouse productionare the United Kingdom (cider), Spain (_sidra_), France (Normandy and Brittany--_cidre_), Germany (_apfelwein_) and Ireland, followed by Poland, Finland, Ukraine, Czech Republic, etc. [7; 8]. Among the fastest growing European cider markets during the 5-years period of 2015-2020, Croatia was in the 6 th place with production of 39,160 hL of cider in 2020, after Moldova, Macedonia, Slovenia, Ukraine and the Czech Republic [9]. The Croatian cider market is characterized by the production of industrial ciders, mostly flavored ones, with some individual enthusiastic attempting of making craft ciders from old Croatian apple varieties that were never analyzed in this context. Although pushed out by commercial apples, traditional varieties of apples with a long tradition of production, mostly collected and described in the Plant genetic resources bank [10] are a valuable resource and natural heritage in Croatia, receiving more scientific attention recently [11; 12; 13]. According to previous research, apple variety has the primary attribute influencing the volatile composition of cider [14], together with control of the ripening stage [13], which opens the wide area of analyzing the potential and role of traditional Croatian apple varieties in the growing cider market. The term cider is usually a synonym for cyder, but in some countries cyder can mean apple juice or non-alcoholic beverage, in the USA, which has undergone growth in its production, fermented apple juice is known as hard cider [7]. As an alcoholic beverage, cider can be obtained by complete or partial alcoholic fermentation of fresh apple juice, diluted apple juice concentrate, or a mixture of both [2; 15]. The alcohol content, in Europe, is within the range of 1.2% to 8.5% alcohol by volume (ABV) and the adding of distilled alcohol is forbidden. Depending on the ABV, ciders can be classified as soft ciders (1-5%) or hard ciders (6-7%) [16]. Reduced-alcohol ciders on the European market are classified as alcohol-free ciders (<0.5% ABV) or low-alcohol ciders (0.5-1.2% ABV) [2]. Furthermore, ciders can be dry (<20 g:L\({}^{-1}\)), semidry (30-50 g:L\({}^{-1}\)) or sweet (>50 g:L\({}^{-1}\)). While sweet ones contain residual sugar from fermentation, or are sweetened after, dry ciders do not contain sugar, with 6-7% ABV. Still ciders have a low sugar content and do not contain carbon dioxide (CO\({}_{2}\)), while sparkling ciders have a low sugar content and an alcohol content higher than 3.5% ABV, with partial retention of the CO\({}_{2}\) formed during fermentation or carbonation [7]. Sparkling cider can be made by traditional or _champenoise_ method characterized by secondary fermentation in the bottle. Additional fermentation of still, base apple wine (5-6% ABV) is mixed with a combination of yeast strains, sugar liqueur and bentonite resulting in sparkling wine with 9-10% ABV.