History of Natto and Its Relatives (1405-2012 - SoyInfo Center

cooked beans.
(d) Cooking: Almost all cooking is presently done in
steam-trapping pressurized vats, 60 kg (4 tô) capacity, 70
kg (5 tô) capacity and 120 kg (6 tô) capacity vats being
equipment in standard use. See Fig. 8.3 (photo of pressure
cooker). Gradually, more and more stainless steel vats are
coming into use. The newest vats are cylindrical with hand or
electric-powered mechanisms for rotating the drum, thus not
only eliminating any unevenness of cooking and facilitating
removal of the cooked beans, but also occasionally allowing
for the natto bacteria inoculation to occur in the vat with
the following step of mixing accomplished by rotating the
drum. In cooking, the pressure inside the vat is allowed to
reach 1 to 1.5 kg/cm squared, and maintained at that level for
20-30 minutes, after which time the pressure cook is opened
slightly to allow the pressure to fall.
(e) Natto bacteria inoculation and packing: The natto
bacteria used is that sold directly from the specialist
manufacturer of inoculant bacteria, available in either liquid
or powdered form, though both contain approximately 1-10 x
10 7 natto bacteria spores per gram. Usually 5 gm of inoculant
bacteria diluted in 3-5 liters of sterilized water is used per
60 kg of soybeans. The normal method of inoculation is to
sprinkle the dilute bacterial solution or to pour it with a ladle
over the cooked beans while they are still 80ºC or above.
Figures show: 8.1 Flowchart of natto production. Tables
show: 8.3 Soybean characteristics by size and by growing
region. The regions are: Koganeshiro: Tokachi, Kitami,
Kitamishiro: Takachi, Kitami. Tokachi-nagaha: Tokachi.
For each sub-region are given fi gures for large, medium,
and small soybeans–15 in all. For each of the 15 soybean
types, the following fi gures are given: Distribution by bean
size (percentage; totals 100% for each region). Seed to coat
ratio. Weight per 1,000 beans (gm) (ranges from 272 to 131).
Water absorbency (%) after 8 hours, 15 hours, and 24 hours.
Percentage of eluted solids (yôshitsu kokei-bun) after 24
hours. Note: Elution is a term used in analytical and organic
chemistry to describe the process of extracting one material
from another by washing with a solvent.
Table 8.4. Soybean composition by size and by growing
region. The 3 regions and 5 sub-regions are the same as
in table 8.2. For each of the 15 soybean types is given
percentage of moisture, protein, fat, carbohydrate, ash, total
sugars (zentô). Continued. Address: National Food Research
Inst., Tokyo.
581. Watanabe, Tokuji; Ebine, Hideo; Ohta, Teruo. eds.
1971. Nattô [Natto]. In: Tokuji Watanabe, H. Ebine and T.
Ohta, eds. 1971. Daizu Shokuhin [Soyfoods]. Tokyo: Korin
Shoin. 271 p. See p. 123-38. [Jap; eng+]
• Summary: Continued. As soon as inoculation is completed,
a standard measure of the cooked beans is immediately
packed into containers. This packing step is the step lagging
most behind mechanization in natto’s production process.
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HISTORY OF NATTO AND ITS RELATIVES 199
Although an automatic measuring and packaging machine to
pack a standard measure of the cooked beans into containers
without harm will no doubt be developed someday, at present
this step is largely done by hand. One reason is that the
containers used are specialized and of many types.
(f) Containers: The packaging containers for natto
are made of straw, then wood sheets, man-made paper,
polyethylene, high-density polyethylene (a kind of HDPE,
haizekkusu = Hai-Zex, developed by Suzuki Chemical Co.),
polystyrene, etc. alone or in combination. Although with
straw and wood sheeting, there are problems of sanitation
caused by the presence of many unwanted bacteria, the
image of simplicity presented by such materials is well suited
to a traditional food such as natto, and many consumers like
such packaging. Thus, straw and wood sheeting are used,
having been sterilized fi rst.
(g) Fermentation chamber: Up until a few years ago,
natto was made in insulated double-wall fermentation
chambers, the temperature being controlled by charcoal fi re
or electric heat, and the moisture level being maintained by
boiling water in the chamber, but since the development of
automatic natto production equipment, natto can now be
made without the constant care that was formerly required.
The principle behind this change of improved insulation,
thus accommodating and averaging of fermentation chamber
interior temperature and moisture levels.
The natto bacteria on the cooked beans germinate
around the optimum temperature of 40ºC. At this time,
heat is not yet produced by fermentation, so a pilot light
is used to prevent the chamber temperature from falling
below 40ºC. Some 4-6 hours after placement in the
chamber, a fermentative heat accompanying the natto
bacteria preparation arises, and both the temperature of
the product and of the chamber increase. The equipment
is set so that cooling will come on during this time if the
chamber temperature rises to 42-45ºC and above. Within
approximately 6-8 hours, the product temperature climbs
to 50-53ºC. After several hours at this temperature, the
product temperature is cooled to external air temperature
and fermentation is stopped approximately 14-18 hours after
placement in the chamber. To prevent the moisture level in
the fermentation chamber from reaching the dew point under
the forced-air cooling, care is taken to prevent excessively
moist air from being cycled into the chamber.
(h) Storage and transport: Once fermentation is
completed, the natto is taken out of the fermentation
chamber, cooled to 10ºC and below in a cooling chamber and
then shipped. In case it is not to be shipped it is kept at 2-7ºC
in a refrigeration room.
(i) Natto production results: The ingredient soybeans
vary somewhat, but 100 parts soybeans will produce 220
parts cooked soybeans and 200 parts natto.
8.1.6 Compositional changes in the soybean during the
natto production process: (a) Chemical change: As natto