## 1 Introduction  
Blueberries are known to taste both sour and sweet and have a mellow bouquet. Upon consumption, blueberries can not only supplement various vitamins and trace elements, but also enhance immune function and anti-aging, especially having an obvious protective effect on cardiovascular disease and renal failure [1]. However, blueberries are extremely susceptible to decay during storage and processing; thus, blueberry wine provides an alternative method to preserve nutrition and extend sales time [2,3]. However, the current strain used for blueberry wine is generally just _Saccharomyces cerevisiae_, which makes the flavor of blueberry wine relatively simple and cannot meet the demand of current consumers for blueberry wine with various flavors.  
At present, ester-producing yeasts received significant attention for their role in both ethanol yield reduction and flavor enhancement in wine [4,5]. Studies found that ester-producing yeasts, belonging to the genera of _Hansenispora_, _Candida_, _Metschnikowia_, _Pichia_, _Wickerhammyces_, and _Toruslspora_, had some desired oenological features that were absent in _S. cerevisiae_, which could make up for the deficiency of pure fermentation of _S. cerevisiae_[6, 7, 8, 9, 10]. Ester-producing yeasts can change the fermentation environment, flavor, and quality of wine in two ways. One way is that ester-producing yeasts can catalyze the release of volatile aroma compounds from non-volatile precursors [11]. Studies showed that ester-producing yeasts could secret enzymes (esterase, \(\beta\)-glycosidase, lipase, and protease) that hydrolyze glycosylated odorless precursors in grapes to form free volatile aroma compounds, thus improving the flavor of grape wine [12; 13; 14]. [PERSON] et al. found that high concentration of volatile aroma compounds was detected in wine treated by \(\beta\)-glucosidase from _Pichia anomala_[15]. Another way is that ester-producing yeasts can directly produce volatile aroma compounds through their metabolic activities [16]. For example, _Williopsis saturnus_, recently renamed _Cyberlindhera saturnus_, could produce a large number of ester compounds (phenylethylly acetate and isoamyl acetate) in cider fermentation [17]. [PERSON] et al. also improved the quality of apple cider by co-fermentation of _Wickerhamomyces anomalus_ and _S. cerevisiae_[18]. The mixed fermentation of _P. anomala_ and _S. cerevisiae_ could also improve the sensory quality of cane wine because their co-fermentation increased the volatile compounds that were associated with a good sensory description [19]. Among them, ester compounds formed by the reaction of alcohol and carboxylic acids are vital volatile aroma compounds that contribute to the flavor characteristics of fruit wine [20; 21]. Therefore, the co-fermentation of ester-producing yeasts and _S. cerevisiae_ is an attractive strategy to increase the content of ester compounds, thus improving the flavor of blueberry wine [22].  
In our previous study, ester-producing yeasts (_Candida glabrata_ NCUF308.1 (E4), _P. anomala_ NCUF306.1 (E1), and _W. anomalus_ NCUF307.1 (E3)) with strong abilities of ester production were selected from blueberry peel and fermented _[PERSON]_[23]. Therefore, three kinds of ester-producing yeasts and _S. cerevisiae_ NCUF309.2 were used to simulate the co-fermentation of blueberry wine under different inoculation ratios, respectively. The growth of yeasts, fermentation characteristics, and the accumulation of ester compounds during the fermentation were studied to obtain the optimal ratio of _S. cerevisiae_ and ester-producing yeast for the co-fermentation of blueberry wine. Our results lay the foundation for the further analysis of the application of ester-producing yeasts and _S. cerevisiae_ in blueberry wine.