Production of red mold rice using a modified Nagata type koji maker.

In this research, a commercial koji maker with a rotary perforated bed of 5-m diameter was modified for red mold rice production. Monascus purpureus BCRC 31499 was selected for its high production capacities of monacolin K and red pigment. The selected strain was first cultivated in a 120-l submerged type fermentor at 34 degrees C and 2 vvm aeration rate with 60 rpm agitation for 5 days using 20% liquefied rice porridge as carbon source. The high concentration red mold rice broth (>3.5 g/ml) was harvested for inocula and well mixed with cooked rice to an initial concentration of 2% v/w. The inoculated cooked rice then was directed into the modified koji maker, in which temperature and humidity profiles were kept at varied levels at different stages, respectively. Air was circulated to remove fermentation heat while the perforated bed rotated slowly for providing mild agitation. Lag phase of the Monascus sp. in the modified koji maker was determined to be 16 h by the time the koji temperature raised rapidly. Water was added into the koji bed by a water curtain at the 36th hour to keep the moisture content of the rice koji at 50% or above. At the final stage, temperature was adjusted to 34 degrees C to direct red pigment production. After 7 days, 1,200-kg high quality red mold rice was harvested per batch. Labor costs, space, and fermentation time were reduced tremendously compared with those made by traditional methods.