# How Different Fermentation Type Affects Volatile Composition of Plum Jerkums
## 1 Introduction  
Oenological parameters, volatile compounds, and overall quality of fruit wines depend on the impact of various factors, such as quality of raw materials, mainly their chemical composition, primary processing techniques, fermentation conditions, further vinicitation procedures, and possibly aging. Volatile compounds in alcoholic beverages produced with various fruits have a very diverse origin. Some of them naturally occur in fruits and could be exposed to various transformations carried out by microorganisms during fermentation or aging and oxidation. Other aroma compounds are produced by microorganisms, e.g., esters, volatile acids, higher alcohols, carbonyl compounds, and some terpenoids. However, chemical composition of fruits is a key factor to fruit wine quality [1, 2, 3].  
Plum (_Prunus domestica_) could be used for winemaking or for cider-like alcoholic beverages--plum jerkum is produced in Central England. Plum wine, which is particularly popular in Germany and Pacific Coastal states, has an appealing color and is high quality. Plum could be tart and sweet at the same time which originates from the concentration of sugars and acids. The skin itself might be particularly tart [3].  
Fresh plums contain, e.g., ethyl acetate, 2-methyl-l-propyl acetate, propyl acetate, 3-methylbutyl acetate, butyl acetate, pentyl acetate, 3-hexenyl acetate, 1-hexanol, (Z)-3-hexenol, nonanal, linalo, benzaldehyde, \(\gamma\)-octalactone, \(\gamma\)-decalactone, and others which contribute to the aroma of alcoholic beverages [4]. Presence of these substances gives them a fresh, fruity, and floral aroma.  
Microorganisms which carry out alcoholic fermentation are either indigenous microorganisms present on fruits or added starter cultures. Initially, in spontaneous fermentation,musts are dominated by yeast which belong to _Kloeckera/Hanseniagpora_, and _Candida_ genera. In the middle stages of fermentation when the concentration of ethyl alcohol rises to 3-4%, mainly species of _Pichia_ and _Metschnikowia_ are present [5]. After that, when ethanol concentration is high, _Saccharomyces_ yeast dominates fermentation. However, in the majority of cases, wine producers use starter cultures of _S. cerevisiae_. This approach enables obtaining wine of consistent quality [5]. _Saccharomyces_ yeast could produce various volatile compounds--esters, especially ethyl acetate, diethyl succinate, ethyl caproate, ethyl caprylate, methyl anthranilate, aldehydes, ketones, and terpenes, e.g., linaol, linaolol oxide, guaiaol, \(\beta\)-ionone, and citral. It also provides high sensory quality of alcoholic beverages [1,6].  
_H. uvarum_ could produce increased amounts of volatiles that improve fruit wine quality such as higher alcohols, esters, and carbonyl compounds. Therefore, mixed cultures of _S. cerevisiae_ and _H. uvarum_ could be used for the production of fruit wine with improved aroma and quality. Among wild yeast, _H. uvarum_ strains could synthesize a significant quantity of acetic acid and ethyl acetate which could spoil wine quality when in excess [7].  
The current study mostly focuses on assessing the impact of microbial fermentation on chemical composition and the volatile profile of plum jerkums. For the fermentation, spontaneous fermentation, _S. cerevisiae_ S1, _H. uvarum_ H2, and Ethanol RED (_S. cerevisiae_) were used. _S. cerevisiae_ and _H. uvarum_ strains were isolated during the fermentation of Cacanska Lepotica or Wegierka Dabrowicka, respectively. In this study, four cultivars of plums were used: Stanley, Wegierka Zwykla, Wegierka Dabrowicka, and Cacanska Lepotica. The first three of them are commonly cultivated in Poland and used for processing in the food industry [8], while Cacanska leptotica has great potential for fruit wine production [9].