We analyzed the physicochemical properties of commercially available top-fermented beer (ale) and bottom-fermented beer (lager) marketed in Korea to compare the quality characteristics. The following characteristics of beer were analyzed for their soluble solid content, pH, total acid content, alcohol content, volatile acid content, reducing sugar content, amino acidity, and color. As results, the pH ranged from 4.01 to 4.77, 0.10-0.23 (%) for total acid and 0.25-1.47 (mL/10 mL) for amino acidity. The alcohol content was in the range of 3.10-5.70 (%) for ale and 3.80-5.20 (%) for lager. The volatile acid content was in the range of 28.67-97.93 (mg/L) for ale and 32.80-78.87 (mg/L) for lager. Regarding the color, the EBC value of the ale beers was in the 4.78-93.98 range, and that of lager beers were in the 5.48-11.98 range. Comparison of the quality characteristics of the two types of beer, revealed differences in pH, amino acidity, total acid content, reducing sugar content, and color. In particular, total acid content (t=−3.782, p⟨0.05), reducing sugar content (t=−11.744, p⟨0.05), and color (t=−2.882, p⟨0.05) of ale beer showed significantly higher than those of lager beer.
Nuruk is a traditional Korean fermentation starter containing various microbes; it is utilized for the synthesis of alcoholic beverage. In this study, the changes in the quality characteristics and microbial community during the cultivation period of nuruk were analyzed. The results indicated that the fungal richness, expressed as Chao 1, from 70.0 to 19.3 on day 10 and subsequently increased to 35.0 on day 30 of cultivation. The content ratio of Aspergillus sp., Rhizopus sp. and Saccharomycopsis sp. increased with the progress of cultivation. Among the fungi, the content of the Aspergillus genus increased from 0.01% before cultivation to 70.4 %. Among the bacteria, the content of the Pantoea genus increased to 69.76% on day 7 and decreased to 44.80% on day 14. Considering the enzyme activity, saccharogenic power, α-amylase and carboxy peptidase exhibited the highest activity on day 7 while lipase exhibited the highest activity on day 14. Considering only the enzyme activity, the results indicated that it would be appropriate to terminate cultivation before day 14. The traditional cultivation period of nuruk is approximately 14 days; However, it is necessary to determine a suitable cultivation period for the application of nuruk as enzyme source.
This study was carried out to investigate the quality characteristics of 'Kaoliang' spirit by grain materials for developing the Korean-style 'Kaoliang' spirit. Each grain was crushed for solid fermentation, and re-fermentation was performed three times in total. There was no significant difference in temperature during solid fermentation by different grains, but it rose to up to 31℃ until the first two days of fermentation, and then the fermentation was completed while maintaining 27℃. Agglomeration occurred in solid fermentation using wheat, resulting in lower work efficiency than other grains. The total acids increased after fermentation, and was the highest at 0.77% in distilled spirit using sorghum, and the major organic acids were lactic acid and acetic acid. A lot of glycerol and glucose were detected, and after three re-fermentation, all sugars were converted to ethanol. Through three re-fermentation, ethanol was the highest in distilled spirit using corn and barley. The volatile compounds, ethyl acetate, ethyl butyrate, and ethyl lactate, were detected at the high level in distilled spirit using sorghum, and the highest ethyl caproate component in using wheat. Therefore, this study proposed to use the mixed grain materials, sorghum and wheat, in order to increase the production of ethyl caproate, the main aroma compound in 'Kaoliang' spirit.
This study demonstrated the effects of different commercially available Saccharomyces cerevisiae yeasts i.e., Fermivin ® , La Parisienne, Songcheon, Ottogi, and Chungmoo, on the variation in the quality of yakju samples under accelerated aging (45℃, 14 d). The analyses of physicochemical properties of the yakju samples were performed for, soluble solid content (°Brix), pH, total acid content (%, as acetic acid), alcohol (v/v%), volatile acid (mg/L), reducing sugar content (mg/mL), amino acidity (mL), brownness (A 430 ), and hunter color value before and after aging. By comparing the results, significant differences in the properties of the yakju samples before and after aging were observed. The yakju sample fermented with wine-yeast Fermivin ® exhibited no significant change in color after aging; furthermore, the reducing sugar content (1.20±0.01-1.32±0.03 mg/mL) and amino acidity (4.06±0.07-4.80±0.04 mL) of this sample were lower than those of the other samples. The yeast of Fermivin ® resulted in a negligible residual sugar content owing to complete fermentation, thereby minimizing the variation in quality during aging. The using of different yeasts for fermentation induced significant differences in the contents of organic acid, free nitrogenous components, and volatile components before and after aging. The obtained results indicated that the properties of yakju such as odor and browning, could be regulated based on the type of yeast used for fermentation.
This study aimed to control sugar consumption during makgeolli fermnetation using high temperature treatments after 3 days of fermentation at normal temprature. makgeolli fermentation was performed at 25°C for the initial 3 days and at 34, 37, 40, and 43°C, respectively, for the next 4 days. When fermented at 25°C (control), the alcohol content increased up to 16.5%; however the alcohol content of makgeolli treated at elevated temperatures reduced by 13.8 %. In the control group, typical saccharification and fermentation proceeded simultaneously, and the reducing sugar content remained low due to sugar consumption by active yeast. However, at high fermentation temperatures, the nuruk enzymes functioned normally and saccharification proceeded well; however the conversion of fermentable sugars to alcohol was inhibited, possibly due to a decrease in yeasts activity. The viable cell count of yeasts was 4-6 log CFU/mL regardless of the fermentation temperature. These results indicate the possibility of producing sweet live-yeast makgeolli without the addition of artificial sweeteners through a temperature-controlled makgeolli fermentation.
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