4 BULLETIN 1152, U. S. DEPARTMENT OF AGRICULTURE. 
Fig. 2. — Japanese koji room (exterior). 
The preliminary mold fermentation of shoyu is best carried on in 
shallow trays made of wood (fig. 1), each separated from the others 
by wooden legs placed on the corners of the bottom of the tray. The 
inside measurements of the trays were 17 by 8 inches, with a depth 
of 2£ inches. A soft wood, neither shellacked nor coated, was used. I 
The trays, therefore, could absorb moisture to an extent sufficient to 
keep condensed water from running down upon the koji. 
For experimental purposes a case, 38 inches long, 28 inches high, 
and 22 inches deep (fig. 1), was constructed to serve as a koji room, 
or compartment, for the trays. Sixteen trays were stacked in two * 
tiers in this case, with 2 inches of air space between the two tiers of 
the trays and on the four sides, and a space of 3 inches from the 
uppermost tray to the top of the case and one of 9 inches from the 
bottom of the case to the lowest tray. This greater space at the 
bottom of the case prevented an electric plate which was introduced 
from heating any one tray too intensely. The electric plate kept 
the miniature koji room from Jbecoming too cool in a cold season. 
It was insulated with asbestos to guard against ignition of the 
wooden case. The air space as a whole allowed for the absorption of 
moisture generated by the mold growth which occurred during the 
fermentation process. It was found, however, that sufficient space 
was not allowed for this purpose when all 16 trays contained im- * 
mature koji where very active mold growth was naturally going on. 
The case, as well as the trays, was made of nonresinous wood. Its 
temperature and moisture, when not controlled by the fermentation 
process itself, were regulated by means of an electric thermostat, 
supplemented by a blast of cool air. As the case was not air-tight, 
a satisfactory circulation of air was thus secured. 
