10 BULLETIN 1152, U. S. DEPARTMENT OF AGRICULTURE. 
necessary, for the beans and wheat are now bound by the mycelium 
or white threads produced by the shoyu-mold. Every bean should 
be covered with this white growth. If the white mycelium is not 
distinguishable with the trained naked eye, the koji is too immature 
to be disturbed. This immaturity may be due to low viability in the 
spore material, to insufficient inoculum, to low temperatures, or to 
temperatures high enough to allow inhibiting bacteria to grow. The 
koji at its best has a heavy surface felt of mycelium, matting the 
beans and wheat together in a solid cake. There is. however, no ob- 
jection to a scantier growth. Sporulation must not have begun. 
Even the slightest visible indication of fruiting at this age marks 
shoyu koji as being not of the highest grade. This immature koji 
should be spread out and exposed by stirring until it has cooled 
down to 24° or 25° C. (TO to 72° F.) or lower. 
The koji. instead of being leveled at the end of the 18 to 20 hour 
period, is this time heaped in two piles, extending the length of 
the tray. (PL II, B.) The material should come in contact with the 
sides of the tray as little as possible, since condensed water on the 
surface of the saturated wood induces bacterial growth when ab- 
sorbed by the tray or retained by the beans and wheat. The wheat, 
rather than the beans, should be at the surface of the two heaps. 
After the stirring is completed the trays of 18 to 20 hour koji are 
replaced in the koji room where they remain undisturbed until six 
or seven hours later. The temperature of the koji room may now 
be just under 30° C. with safety, while that of the koji itself should 
be between 27° and 29° C. The mycelial growth is now heavier, 
but no sporulation should be evident. 
At the end of this second incubation period, the koji is stirred 
thoroughly a second time, the beans and wheat being broken apart. 
The mass is cooled below 24° C. After this stirring, four furrows, 
running the short way of the tray and forming three heaps, are 
made. (PL II, C.) The trays of koji are again placed in the koji 
room. 
When examined at the end of 40 hours, 12 to 14 hours after the 
second stirring, the surface of the koji should be a clear " flavus " or 
yellow color from the fruiting heads of Aspergillus. This yellow 
color does not develop if the temperature overnight has been 50° to 
55° C, causing a drying and apparent burning out of the surface, 
or if the moisture has been excessive enough to effect bacterial mul- 
tiplication. The temperature of the best koji should now be not 
much above 35° C. although 35° to 36° C. is permissible. Koji with 
a temperature of 42° to 45° C. at the end of 40 hours may appear 
excellent in spite of the high temperature. This is not good factory 
practice, however. a> the greater heat is due to bacterial activity. If 
the temperature of 40-hour koji is over 35° C, the product may be 
cooled to advantage by so breaking apart each heap as to form 
several cracks in the solid mass, or, if more extreme cooling is 
necessary, the koji may be be broken into chunks and turned over, 
leaving exposed as large a surface as is possible. In the climate of 
Washington, D. C, shoyu koji may be carried through the second 
stirring in 30 hours and be mature in less than 2| days. Usually 24 
hours is sufficient for the maturing of the koji, a stage in the fermen- 
tation which extends from the beginning of evident sporulation on 
