Figure 5 Curve showing action of koji extract on gelatinized starch at 1015C

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Time in hours.

Time in hours.

From these experiments we may understand what occurs during the mashing operations in sake making. At first they are conducted at even a lower temperature than 4°C, and this is interesting because it shows that the activity of the diastase in koji is not destroyed at low temperatures, even at 0°C.

At a higher temperature the reduction in the specific rotatory power of the solution goes on more rapidly, and although the sake brewer never uses temperatures so high as those of the succeeding experiments, it is of scientific interest to complete the record at all temperatures below that at which the diastase of koji is rendered inactive.

The experiments at higher temperatures were conducted in the following manner. The flask containing the mixture was immersed in a water bath and kept at the specified temperature, samples being taken at stated intervals. The portion used for determining the total solid matter in solution from its specific gravity was rapidly cooled by means of ice, and another portion in which the specific rotatory power was to be determined, was poured into a dry flask containing a little salicylic acid, as recommended by Brown and Heron*, and also rapidly cooled. Deduction was made for the amount of koji solution added as in the previous experiments.

The two next series of experiments were conducted at 40°C and only differ in the relative proportions of starch and koji used. The first series used 10 grams of starch to 5 grams of koji; the second used 10 grams of starch to 10 grams of koji.

Table 19: Action of koji on starch at 40°C

Time

Total starch in solution (koji deducted)

Specific rotatory power of starch

25 minutes

10.08 grams

167°

4 hours

10.08 grams

127°

> 92 hours at 15°C

10.25 grams

106°

Table 20: Action of koji on starch at 40°C

Time

Total starch in solution (koji deducted)

Specific rotatory power of starch

20 minutes

9.64 grams

143.1°

1 hour

9.64

127

2 hours

9.64

115

3 hours

9.65

105

4-1/2 hours

9.67

88

6 hours

9.69

86

> 20 hours at 15°C

9.79

80

In Figure 6 these results are represented in a graphic manner. The difference between the two sets lies in the fact that in the latter twice as much koji is used as in the former, and the result is that at any given time the diminution in the specific rotatory power is greater in the latter. Further, the general form of the two curves is similar and there is no evidence of any sudden break in the curve, such as in Brown and Heron's experiments indicates a definite chemical equation. Such a break could not be expected, seeing that the action of koji solution upon maltose would tend to disguise such reactions, by rubbing down the corners, as it were. Table 21 gives the results of a similar experiment made at 45°C.

Table 21: Action of koji on starch at 45°C

Time

Total starch in solution (koji deducted)

Specific rotatory power of starch

5 minutes

9.48 grams

142.6°

25 minutes

9.93

126.8

1 hour

9.93

106

1-1/2 hour

-

103.6

2 hours

9.98

103

3 hours

9.98

98.3

4 hours

-

98.3

1/5th more koji added

4-1/2 hours

10.18

88

In the curve in Figure 7 which represents these results graphically, it will be noticed that during the first five minutes the fall in the specific rotatory power is very rapid until it arrives at [ajj = 142.6° after which it proceeds very nearly a straight line until the specific rotatory power equals 106°, after which it remains almost the same, until after a fresh addition of koji, which causes a reduction to 88°. As the rate of reduction after the addition of a fresh quantity of koji is very nearly the same as at first, as is shown by the similarity in the inclinations of the curve, it is evident that the koji first added had been nearly exhausted when the specific rotatory power of 106° was attained.

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