Abstract
This study was conducted to investigate the physiochemical characteristics of Cheongju prepared using different types of rice (rice and glutinous rice) according to addition rate of Nuruk during low temperature fermentation. The characteristics of Cheongju prepared using three different temperatures ($10^{\circ}C$, $18^{\circ}C$, $25^{\circ}C$) were compared. After fermentation for 30-50 days, the pH of mash prepared at lower temperature was lower, as was that of mash made from rice relative to that prepared using glutinous rice. The total acidity was formed at lower temperature and generated in mashing prepared by glutinous rice. The organic acid content of mash made from rice at $18^{\circ}C$ was lowest, while that of mash prepared from glutinous rice was lowest at $10^{\circ}C$. The fermentation speed was lowest at $10^{\circ}C$; however, low temperature fermentation resulted in the highest alcohol content. The mash prepared from glutinous rice showed faster fermentation than that made from rice. In addition, the pH was lower when lower levels of Nuruk were added and higher in mash made from glutinous rice than that prepared from rice. The lower addition rate of Nuruk also showed a lower sugar content and final alcohol content. The levels of citric acid and lactic acid were higher, while those of succinic acid, acetic acid, and ethyl acetate were lower when lower levels of Nuruk were added. The mash prepared from glutinous rice showed a higher alcohol content than that made from rice.
본 연구는 청주의 저온발효 제조시 멥쌀과 찹쌀 등 원료에 따른 이화학적 특성 비교와 누룩투입 비율에 따른 발효 및 청주 품질특성을 연구하는데 목적이 있다. 멥쌀과 찹쌀 청주의 발효온도를 $10^{\circ}C$, $18^{\circ}C$, $25^{\circ}C$로 달리하여 30-50일간 발효시킨 청주의 발효특성 비교에서, 멥쌀과 찹쌀 청주 모두 발효온도가 낮을수록 발효시 pH가 낮았고 최종 술덧의 pH는 발효온도에 따른 차이가 없이 각각 동일하였으며, 같은 온도에서는 찹쌀보다 멥쌀 술덧의 pH가 낮았다. 총산은 발효온도가 낮을수록 적게 생성되었으며 멥쌀보다 찹쌀로 제조된 술덧에서 많이 생성되었다. 멥쌀 술덧의 유기산은 $18^{\circ}C$에서 가장 적게 생성되었고 찹쌀 술덧은 저온발효일수록 적게 생성되었다. $10^{\circ}C$ 저온에서 발효속도는 늦었으나 최종술덧의 알코올농도가 가장 높게 나타났으며, 멥쌀보다 찹쌀을 이용한 술덧의 알코올 발효가 빨랐고 최종 알코올농도도 높았다. 발효온도 $10^{\circ}C$에서 누룩투입비율을 달리한 연구에서는 pH는 누룩투입 비율이 낮을수록 낮았으며 멥쌀보다 찹쌀이 다소 높았다. 누룩투입 비율이 낮을수록 발효초반 가용성 고형분($^{\circ}Brix$)이 낮게 나타났으며 알코올 생성 속도가 늦었고 최종 알코올 농도도 낮았다. 또한 누룩투입비율이 낮을수록 구연산, 젖산은 적게 사과산 호박산, 초산은 많이 생성되었고, ethyl acetate는 적게 생성되었다. 저온발효시 찹쌀 술덧이 멥쌀보다 알코올 생성 속도도 빨랐고 최종 알코올 농도도 높았다.