54
4.4.4.1 Fungal Species Involved
There are several fungal species accepted for production of soy sauce such as
Aspergillus tamarii (Raper and Fennell 1965), Aspergillus sojae (Murakami et al.
1982) and Aspergillus oryzae (Raper and Fennell 1965). These are often referred to
as true koji moulds. These moulds can be differentiated based on their conidial head
colour, size of conidiophores, vesicles, conidia and their growth pattern at 37 °C. A
particular mould for koji production is selected based on certain factors such as its
ability to sporulate, colour and flavour of the final product, length of stalk, enzyme
production and its inability to produce toxins.
During koji fermentation, A. oryzae produces two main groups of enzymes: carbohydreases and proteinases (Aidoo et al. 1994; Chou and Rwan 1995). These
groups of enzymes hydrolyze high molecular weight substrates into low molecular
weight amino acids and peptides which are essential in brine fermentation step. The
dominant moromi yeast in brine fermentation which grows to produce 3% alcohol
is Zygosaccharomyces rouxii. There are several other compounds that add aroma to
soy sauce which are produced by yeasts such as Candida etchellsii and Candida
versatilis (Aidoo et al. 2006).
4.4.4.2 Manufacturing Process
A combined fermentation of soya beans, wheat grains, water and salt results in the
production of soy sauce (Hesseltine 1977; Steinkraus 1989). The industrial production of fermented soy sauce involves three major steps: koji fermentation, brine
fermentation and refining. A flowchart for the manufacturing of soy sauce is shown
in Fig. 4.4.
Industrially, production of soy sauce at a large scale basically involves five operational units: the preparation of raw materials, koji process unit, brine fermentation
unit, pressing and the final refining. Stacked wooden trays having a gap of about
10 cm are used in koji process, each of which is filled up to a depth of about 5–8 cm
(Yokotsuka 1983; Aidoo et al. 1984). Traditionally the moromi process was carried
out in ceramic pots or wooden tanks coated with resins. These have now been
replaced by concrete or steel tanks having a capacity of 10–30 m
3
.
Initially, the soya beans are soaked in water, boiled and mixed with the crushed
or ground wheat. The moisture of this mixture needs to be maintained between 40%
and 45%. This mixture is then placed in large wooden trays and mixed with mould
Aspergillus oryzae or Aspergillus sojae and then allowed to ferment for about a
week at 30 °C in order to form koji. The moisture content of koji should be about
25–30 °C. The function of mould here is to release hydrolytic enzymes to convert
the substrate into low molecular weight compounds. In the next step, the koji is
mixed with brine solution (23% w/v NaCl) in the ratio 1.0:1.5 to make moromi
which later on undergoes fermentation for at least 1 year in order to develop colour
and flavour in soy sauce. In the next step, the fermented moromi undergoes filtration. The soy sauce produced is boiled in order to sterilize it (Nout and Aidoo 2010).
R. Kumari et al.
4.4.4.1 Fungal Species Involved
There are several fungal species accepted for production of soy sauce such as
Aspergillus tamarii (Raper and Fennell 1965), Aspergillus sojae (Murakami et al.
1982) and Aspergillus oryzae (Raper and Fennell 1965). These are often referred to
as true koji moulds. These moulds can be differentiated based on their conidial head
colour, size of conidiophores, vesicles, conidia and their growth pattern at 37 °C. A
particular mould for koji production is selected based on certain factors such as its
ability to sporulate, colour and flavour of the final product, length of stalk, enzyme
production and its inability to produce toxins.
During koji fermentation, A. oryzae produces two main groups of enzymes: carbohydreases and proteinases (Aidoo et al. 1994; Chou and Rwan 1995). These
groups of enzymes hydrolyze high molecular weight substrates into low molecular
weight amino acids and peptides which are essential in brine fermentation step. The
dominant moromi yeast in brine fermentation which grows to produce 3% alcohol
is Zygosaccharomyces rouxii. There are several other compounds that add aroma to
soy sauce which are produced by yeasts such as Candida etchellsii and Candida
versatilis (Aidoo et al. 2006).
4.4.4.2 Manufacturing Process
A combined fermentation of soya beans, wheat grains, water and salt results in the
production of soy sauce (Hesseltine 1977; Steinkraus 1989). The industrial production of fermented soy sauce involves three major steps: koji fermentation, brine
fermentation and refining. A flowchart for the manufacturing of soy sauce is shown
in Fig. 4.4.
Industrially, production of soy sauce at a large scale basically involves five operational units: the preparation of raw materials, koji process unit, brine fermentation
unit, pressing and the final refining. Stacked wooden trays having a gap of about
10 cm are used in koji process, each of which is filled up to a depth of about 5–8 cm
(Yokotsuka 1983; Aidoo et al. 1984). Traditionally the moromi process was carried
out in ceramic pots or wooden tanks coated with resins. These have now been
replaced by concrete or steel tanks having a capacity of 10–30 m
3
.
Initially, the soya beans are soaked in water, boiled and mixed with the crushed
or ground wheat. The moisture of this mixture needs to be maintained between 40%
and 45%. This mixture is then placed in large wooden trays and mixed with mould
Aspergillus oryzae or Aspergillus sojae and then allowed to ferment for about a
week at 30 °C in order to form koji. The moisture content of koji should be about
25–30 °C. The function of mould here is to release hydrolytic enzymes to convert
the substrate into low molecular weight compounds. In the next step, the koji is
mixed with brine solution (23% w/v NaCl) in the ratio 1.0:1.5 to make moromi
which later on undergoes fermentation for at least 1 year in order to develop colour
and flavour in soy sauce. In the next step, the fermented moromi undergoes filtration. The soy sauce produced is boiled in order to sterilize it (Nout and Aidoo 2010).
R. Kumari et al.