Aspergillus oryzae. The moulds are then allowed to grow throughout
the mass of material spread as layers about 5 cm deep for 2–3 days at
25–30 1 C.
In the second, mash ormoromistage, conditions are made anaerobic
so no further mould growth can occur. In soy sauce production, this is
achieved by mixing the kojiwith an approximately equal volume of
brine to give a final salt concentration of 17–20%. Although the
moulds can no longer grow, the activity of a whole battery of hydro-
lytic enzymes continues breaking down proteins, polysaccharides and
nucleic acids to produce a liquid rich in soluble nutrients. Yeasts and
lactic acid bacteria dominate the microflora producing a number of
flavour components and converting roughly half of the soluble sugars
to lactic acid and ethanol so that the final soy sauce normally has a pH
of 4.5–4.9 and ethanol and lactic acid contents of 2–3% and 1%
respectively. The halophilic lactic acid bacterium Tetragenococcus
halophilus (formerly Pediococcus halophilus) and the yeastsZygosac-
charomyces rouxiiandTorulopsishave been identified as being impor-
tant in this stage.
Themoromistage can be quite protracted, lasting up to a year or
more, at the end of which the mash is pressed to remove the solid
residues which may then be mixed with brine to undergo a second
fermentation and produce a lower grade product. The liquid is
pasteurized and filtered, possibly after a period of maturation, and then
bottled.
Rather similar steps are involved in the production of soya bean pastes
known asmisoin Japan andchiangin China. These include up to 40% of
a grain such as rice or barley, use dry salt rather than brine, and employ a
shorter fermentation so the product has the consistency of a paste rather
than a liquid.
In the brewing of the Japanese rice wine,sake,akojiprepared on
steamed rice is used. Although the mould used is the same species as
in soy sauce production,Aspergillus oryzae, the strains used insake
production are particularly noted for their ability to produce amylolytic
enzymes. In themoromi stage, water is added along with strains of the
yeastSaccharomyces cerevisiaespecially adapted to thesakefermenta-
tion. During this stage amylolytic enzymes from the mould continue to
break down the starch in the rice to produce fermentable sugars which
are then converted to ethanol by the yeast. The high alcohol content
of around 20% v/v achieved in such fermentations is thought to be due
to a combination of factors. Particularly important is the slow rate
of fermentation which results from the relatively low fermentation
temperature (13–18 1 C) and the slow release of fermentable sugars. The
high solids content in themoromiis also thought to help in keeping the
Chapter 9 367