# Chemical Characterization of Cider Produced in Hardanger--From Juice to Finished Cider
## 3 Results and Discussion
### Volatile Compounds in Apple Juice and in Cider
In addition, isoamyl acetate, ethyl decanoate, ethyl isobutyrate, and hexyl acetate were present at concentrations above the threshold limit in ciders but not in juice for all cultivars. The volatile aroma in the juices is in accordance with other research findings that contribute to the flavour of apples, which is mainly ethyl butyrate, ethyl hexanoate, butyl acetate,  
Figure 1: Principal component analysis loading plot (**A**) and score plot for cultivars (**B**) for measured esters and C6-alcohols in the collected samples in 2019, 2020, and 2021 for ciders. Aroma compounds in bold letters are in concentrations over the threshold limit. hexyl acetate, 2-methylbutyl acetate, and ethyl 2-methylbutyrate [35]. In general, the total ester content increased (e.g., ethyl isobutyrate, ethyl isovalerate, and ethyl cinnamate) or decreased (e.g., E-2-hexenyl acetate and octyl acetate) during the fermentation process. However, some first increased and then decreased (e.g., ethyl butyrate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, and ethyl dodecanoate). Fatty acid ethyl esters are esters found in the highest concentrations (ethyl butyrate, ethyl octanoate, ethyl hexanoate, and ethyl decanoate). They give a fruity, apple, and sweet flavour (Tables 4 and S5), and are the result of the esterification process of sugar alcohols with fatty acids during fermentation [36; 37]. Among the ethyl esters, ethyl acetate is important for the pleasant and fruity cider flavour at appropriate concentrations [36]; however, this ester was not included in the study. In this case study, statistical differences in individual esters between the cultivars were not produced because of too many varietal factors in the dataset. However, the trend is that ethyl hexanoate, ethyl octanoate, and ethyl decanoate are highest in 'Summerred' cider compared to the other cultivars (as illustrated in the PCA plot, Figure 1). Similar trends between apple cultivars for ciders have also been identified by [PERSON] et al. [38]. The increases in ethyl esters during fermentation are many-folded compared to juice and are affected by the apple variety, pH, sugar, nitrogen, and amino acid composition [38]. Different apple cultivars have different chemical compositions and thus different ester precursors. The precursors for different aromatic compounds are amino acids, carbohydrates, and fatty acids [39]. The YAN concentration in 'Summerred' was, on average, higher in the juices (70 mg L\({}^{-1}\)) than that of the other cultivars (23-38 mg L\({}^{-1}\)) (Table 2). However, further investigation of the amino acid composition is needed to determine the relationship between the YAN/amino acid profile and ester production. The same is true for yeast strains and other technological factors. The aroma profile of apples is dependent on the degree of maturation. Aldehydes are the most abundant aromatic compounds before maturation, and esters are the main group of aromatic compounds in ripe apples. In our study, the ripeness of apple fruit was not identified as the juice samples were delivered by producers. According to [PERSON] [40], unripe apple fruits contain isoamyl acetate, hexyl acetate, butyl acetate, and ethyl hexanoate. C6-alcohols result in a green flavour of cider, and at high concentrations, this can be negative. C6-alcohols are produced during the processing of the fruit via the bioremediation of unsaturated fatty acids, while during fermentation, the C6-alcohol content normally decreases [41]. The hexanol concentrations identified in this study varied a lot between the producers, years, and cultivars. Some increase, some decrease, and some decrease and increase. In apple juice, hexanol is an indicator of ripeness [42].