## 2 Results
### Evolution of Aroma Compounds during Fermentation and Bottle Storage  
Unlike the cold soak stage, the leaching and evolution of aroma compounds occur in the alcohol phase during the fermentation and bottle stages. In the early stages of alcoholic fermentation, a large number of esters, including a variety of ethyl esters and acetates, and a variety of alcohols are produced (Figure S1). A total of 59 free-form and 18 bound-form aroma compounds were identified in 'Merlot' and 'Marselan' during the fermentation stage. The details of concentrations of compounds can be found in Table S2. Free-form ethyl phenylacetate, isobutyl octanoate, (_Z_)-3-hexene-1-ol, 1-pentanol, butanoic acid, octanoic acid, and p-cymene were detected only in 'Marselan', along with bound-form 1-butanol and isobutanoic acid. Conversely, free-form ethyl valerate, ethyl lactate, and decanoic acid, as well as bound-form 4-methyl-2-heptanol and 2-methyl-1-butanol, were identified exclusively in 'Merlot'. During the bottle storage stage, 'Merlot' wine did not contain  
Figure 1: Changes in free–form and glycosidically bound aroma compounds during the cold soak stage. (**A**) clustered heat map analysis; (**B–F**): aroma compounds with typical variation trend in each cluster. In the heat map, the letter F after the compound name represents the free form, and the letter B represents the bound form. free-form heptyl acetate, ethyl isobutyrate and methionol. Additionally, 14 bound aroma compounds were detected, and their component types did not significantly vary between 'Marselan' and 'Merlot'. Figure 2 shows the results of the heat map cluster for free and bound aroma compounds in 'Merlot' and 'Marselan' wines. The compounds were grouped into five clusters (Figure 2), and Figure 2B summarizes the types and quantities of aroma components in each cluster. Figure 2: Changes in free – form and glycosidically bound aroma compounds during the fermentation and one-year bottling stages. (**A**) clustered heat map analysis; (**B**) stacked histogram of the number of aroma compounds contained in each cluster; (**C**–**G**) The changes of the aroma compounds with typical variation trend in each cluster. In the heat map, the letter F after the compound name represents the free form, and the letter B represents the bound form. During the alcoholic and malolactic fermentation stages, the aroma compounds in cluster 1 had a high concentration. However, their concentrations decreased significantly from the beginning of bottle storage and remained stable thereafter. These compounds were primarily bound-form alcohols, as shown in Figure 2C. During the fermentation, 'Merlot' wine had a higher concentration of bound-form benzyl alcohol compared to 'Marselan' wine. However, within the first 3 months of bottle storage, the concentration of bound-form benzyl alcohol decreased rapidly to below the detection limit. The variation trends of both free-form and bound-form 1-octanol were very similar, indicating that the two compounds do not undergo any mutual transformation. Cluster 2 showed a decrease in concentration during the alcohol fermentation stage, followed by a slight increase during the malolactic fermentation. Afterwards, the compounds dropped significantly to a lower level in the first 3 months of bottle storage. The compounds in cluster 2 were dominated by C5-C7 alcohols and acids, as well as ethyl 3-hexenoate and ethyl phenylacetate. Roughly one-third of the compounds were exclusively present in the fermentation stage of 'Marselan' wine, and were not detectable in the 'Merlot' wine. The two varieties showed similar declining rates for the aroma compounds detected simultaneously, with only a difference in concentration, such as free-form citronellol and 1-hexanol (Figure 2D). Aroma compounds in cluster 3 exhibited minimal fluctuation during the fermentation and bottle storage stages, and their concentrations did not differ between the two varieties. This cluster included free (_E_)-\(\beta\)-damascenone.