# Microbial Community and Functional Analysis of Regionally Produced Traditional Korean Grain Vinegar
## 3 Results  
### Analysis of Grain Vinegar According to Manufacturing Environment  
In this study, four traditional vinegar production companies in Korea were selected, and four types of grain vinegas were collected and analyzed. The regions chosen for this study were Gangwon state, Gyeonggi-do, Jeonbuk state, and Gyeongsangbuk-do. The raw materials used in the production of grain vinegas were brown rice, barley, rice, and a five-grain mixture (brown rice, barley, sorghum, millet, and foxtail millet) in the respective regional order (Figure 1). All four vinegar production processes were conducted without commercial starter cultures. Instead, each manufacturer used previously fermented and stored vinegar as a starter, adding it at approximately 10% (\(v/v\)) to the alcoholic base to initiate acetic acid fermentation. The fermentation period was standardized at three time points: the start of acetic acid fermentation (day 0), the 10 th day, and the end of fermentation (day 20). Sampling was performed after confirming that all the manufacturers followed the same fermentation schedule (Table 1).  
The brown rice vinegar (HB) from Gangwon state was fermented in earthenware jars at a temperature of 28-30 \({}^{\circ}\)C, with acidity measured at 1.60% at the start of fermentation (HBI) and 4.87% on day 20 (HB3). The barley vinegar (SB) from Gyeonggi-do was fermented in a glass container at 30 \({}^{\circ}\)C, starting with 1.41% acidity (SB1) on day 0, increasing to 2.51% on day 10 (SB2), and finishing at 6.83% on day 20 (SB3). The rice vinegar (JR) from Jeonbuk state was fermented in earthenware jars at 30 \({}^{\circ}\)C, with acidity measured at 1.22% on day 0 (JR1), 2.52% on day 10 (JR2), and 5.43% on day 20 (JR3). This acidity range is consistent with reported data indicating that commercially available grain vinegas have an acidity of between 4% and 6%, confirming sufficient acetic acid production and validating the appropriateness of the fermentation time points [22; 23]. The five-grain vinegar (YO) from Gyeongsangbuk-do was fermented in a stainless-steel container at 30 \({}^{\circ}\)C. Its initial acidity was determined to be 8.54% on day 0 (YO1), which is very high compared to the other  
Figure 1: Collection of grain vinegas according to region in Korea.  
samples. This relatively high initial acidity may be due to either a high inoculation ratio of the finished vinegar or the use of vinegar with a high acetic acid concentration as the starter. On day 10, the acidity increased slightly to 9.53% (YO2), with the final value being 14.67% on day 20 (YO3), a relatively high acidity level. Compared to the initial acidity, the final acidity of HB, SB, and JR increased approximately 3-5 fold, while that of YO increased only about 1.7-fold. This difference is likely due to the manufacturing method, where the fermentation mash is inoculated with prepared vinegar rather than using a starter culture. The varying proportions of fermentation mash and seed vinegar may account for these differences in acidity levels.  
The type of vessel used in vinegar production can significantly influence the fermentation environment, thereby affecting the acidity, functional components, and microbial community structure of the final product. Earthenware vessels, due to their porous nature, facilitate effective air and moisture exchange, which can enhance the activity of aerobic microorganisms such as acetic acid bacteria (_Acetobacter_ spp.). Fermentation in earthenware vessels has been reported to support a more balanced microbial community, leading to increased acidity and higher concentrations of organic acids ([PERSON], 2016). In contrast, glass and stainless-steel vessels, while resistant to external contamination, provide limited temperature and humidity control, which may negatively affect microbial growth. These findings suggest that the physical properties of fermentation vessels play a crucial role in shaping microbial communities and determining vinegar quality.