Kōji Preparation

Question 1

What is kōji?

Answer 1

Aspergillus oryzae

A filimentous fungi (mould) grown on cereal grains

Question 2

What percentage of premium sake must be made of kōji?

Answer 2

Minimum 15%

Question 3

Can sake be made only from kōji?

Answer 3

Yes, but this practise is rare.

Question 4

What does the Japanese term kōji-muro mean?

Answer 4

The special temperature- and humidity-controlled room where kōji is cultivated on steamed rice.

Question 5

How does the kōji-kin convert starch to sugar?

Answer 5

The mould grows by sending feeding tubes (hyphae) into the rice grain.
The hyphae secrete enzymes.
The starch is broken down into glucose.
The glucose is absorbed by the hyphae and used to promote further growth.

Question 6

Kōji-kin does not just produce starch to sugar conversion enzymes. What else does it produce?

Answer 6

• Amino acids and peptides (yeast nutrients and umami)
• Vitamins (yeast nutrients)
• Lipids and proteins
• Subtle flavours and aromas, specifically chestnut

Question 7

True or false:

The main acids in sake are produced by the kōji-kin.

Answer 7

False.
Kōji-kin produces very little acidity. The main acids in sake (lactic, succinic and malic) come from the fermentation starter and the yeast

Question 8

What are the three varieties of kōji-kin?

Answer 8

Black
White
Yellow (generally the best choice for sake production as it produces little citric acid)

Question 9

What are the two formats of kōji-kin that can be purchased by brewers?

Answer 9

• Powdered (mould spores)

- Granulated (rice with mould spores on it - the traditional option and still sometimes preferred for ginjō)

Question 10

What are the two styles of kōji?

Answer 10

Sō-haze

Tsuki-haze

Question 11

What is sō-haze?

Answer 11

The kōji-kin covers the entire rice grain.
Produced with higher moisture content.
Causes a fast conversion and a warm, fast fermention for body and flavour.

Ideal for fūtsu-shu and for premium sake with intense flavours, full body, high acidity and high umami.

Question 12

What is tsuki-haze?

Answer 12

The kōji-kin grows in a lightly spotted pattern over the rice grain.
Most of the growth is in the centre of the grain.
Produced with lower moisture content
Requires a high level of skill to produce (restricted spores, warm room with less humidity)

Causes the long, slow and controlled fermentation that is required for ginjō and daiginjō aromas. Also used for honjōzo with lean texture and restraint.

Question 13

True or false:

Lipids can inhibit the formation of ginjō aromas and flavours

Answer 13

True.

Lipids are present in the outer parts of the endosperm and are also produced by the kōji, especially sō-haze kōji.

Question 14

Why is traditional kōji making very labour intensive?

Answer 14

Temperature and humidity need to be checked every two hours.

Rice needs to be constantly worked by hand.

Question 15

Is all kōji made by hand?

Answer 15

No - all or parts of the process can be mechanised.

Even some small and artisan producers are starting to use this as the technology has improved so much. However mechanisation has not yet gotten to the stage that can replicate the very best handmade tsuki-haze.

Question 16

What is the ‘bringing in’ stage of kōji production?

Answer 16

• Temperature of steamed rice brought down to 32-35°C
• Steamed rice transferred into the kōji room
• Steamed rice is laid out on the toko - large shallow bed

In Japanese: hikikomi

Question 17

What are the ‘spreading the spores’ and ‘initial mould growth’ stages of kōji production?

Answer 17

• Occurs 1-3 hours after bringing in until hours 10-12
• Temperature of rice raised to 33-35°C
• Spores are evenly spread out on the rice using a hand shaker
• Rice grains are formed into a mound and covered in blankets to retain heat (the mould creates heat as it grows)
• Left like this 8-10 hours

In Japanese: tanekiri

Question 18

What does the Japanese term hikikomi refer to?

Answer 18

The first stage of kōji production called ‘bringing in’

Question 19

What does the Japanese term tanekiri refer to?

Answer 19

The second stage of kōji production called ‘spreading the spores’ and ‘initial mould growth’

Question 20

What is the ‘re-breaking up’ stage of kōji production?

Answer 20

• The mould has begun to spread unevenly on the rice during the initial mould growth stage
• The rice is unwrapped from the blanket and spread back over the toko (bed)
• Any clumps are broken up and the grains are worked through
• The rice is wrapped up again to allow mould growth for another 8-12 hours

In Japanese: kirikaeshi

Question 21

What does the Japanese term kirikaeshi refer to?

Answer 21

The third stage of kōji production called ‘re-breaking up’

Question 22

What is the ‘mounding’ stage of kōji production?

Answer 22

• carried out half way through production
• the aim is to manage the level and distribution of mould growth - the growth pattern has not yet been determined
• the brewer controls temperature and moisture at the level of the single rice grain
• choice of bed kōji / box kōji / tray kōji
• mould growth continues for 7-10 hours

In Japanese: mori

Question 23

What does the Japanese term mori refer to?

Answer 23

The fourth stage of kōji production called ‘mounding’

Question 24

What does the Japanese term toko-kōji refer to?

Answer 24

Bed kōji

The entire kōji process is made on the toko bed.

• big batches of kōji (100-300kg)
• does not allow the most precise control of kōji growth
• mould growth continues for 7-10 hours

Used for futsū-shu, honjōzō and junmai. Sometimes used for ginjō. Unsuitable for daiginjō.

Question 25

What does the Japanese term futa-kōji refer to?

Answer 25

Tray kōji

The kōji rice is transferred from the toko bed into small containers called futa.

• tiny batches of kōji (1.5 - 2.5kg)
• the most precise control of kōji growth
• very labour intensive
• the trays are arranged in racks and checked and rotated every few hours
• mould growth continues for 7-10 hours

Used for the best daiginjō.

Question 26

What is bed kōji?

Answer 26

Toko-kōji

The entire kōji process is made on the toko bed.

• big batches of kōji (100-300kg)
• does not allow the most precise control of kōji growth
• mould growth continues for 7-10 hours

Used for futsū-shu, honjōzō and junmai. Sometimes used for ginjō. Unsuitable for daiginjō.

Question 27

What is box kōji?

Answer 27

Hako-kōji

The kōji rice is transferred from the toko bed into medium-sized boxes called hako.

• medium batches of kōji (15-40kg)
• moderate control of kōji growth
• a divider in the box allows the brewer to slide the rice from one half to the other to control mould growth.
• the boxes are arranged in racks and checked and rotated every few hours
• mould growth continues for 7-10 hours

Too time intensive for futsū-shu. Used for honjōzō and junmai. Sometimes used for ginjō. Not accurate enough for daiginjō.

Question 28

What is tray kōji?

Answer 28

Futa-kōji

The kōji rice is transferred from the toko bed into small containers called futa.

• tiny batches of kōji (1.5 - 2.5kg)
• the most precise control of kōji growth
• very labour intensive
• the trays are arranged in racks and checked and rotated every few hours
• mould growth continues for 7-10 hours

Used for the best daiginjō.

Question 29

What does the Japanese term hako-kōji refer to?

Answer 29

Box kōji

The kōji rice is transferred from the toko bed into medium-sized boxes called hako.

• medium batches of kōji (15-40kg)
• moderate control of kōji growth
• a divider in the box allows the brewer to slide the rice from one half to the other to control mould growth.
• the boxes are arranged in racks and checked and rotated every few hours
• mould growth continues for 7-10 hours

Too time intensive for futsū-shu. Used for honjōzō and junmai. Sometimes used for ginjō. Not accurate enough for daiginjō.

Question 30

What is the ‘middle work’ stage of kōji production?

Answer 30

• The temperature of the rice is controlled by creating larger surface area
• The mound of rice is flattened and patterns drawn into the surface
• Mould growth is at its strongest after mounding and excessive heat produced can kill the mould

In Japanese: naka-shigoto

Question 31

What can occur if the mould dies due to excess heat during the kōji-making process?

Answer 31

• off aromas and flavours (like sweat) produced by dying mould
• mould growth stops at an earlier stage than intended

Question 32

What does the Japanese term naka-shigoto refer to?

Answer 32

The fifth stage of kōji production called ‘middle work’

Question 33

What does the Japanese term shimai-shigoto refer to?

Answer 33

The sixth stage of kōji production called ‘final work’

Question 34

What is the ‘final work’ stage of kōji production?

Answer 34

• focus shifts from controlling heat to controlling moisture
• continue to dry out the rice grains
• continue to release the heat caused by the mould growth (temperature controlled between 38-43°C)
• tsuki-haze is produced by making the surface of the grain drier than the centre, so the mould is encouraged to seek moisture at the centre

In Japanese: shimai-shigoto

Question 35

What is the ‘sending out’ stage of kōji production?

Answer 35

• occurs at hours 44-48
• the temperature of the rice is cooled to ambient temperature
• kōji mould growth is stopped by cooling and drying out the grains, often fans are used

In Japanese: de-kōji

Question 36

What does the Japanese term de-kōji refer to?

Answer 36

The seventh and final stage of kōji production called ‘sending out’

Question 37

Can kōji mould growth be stopped by heating?

Answer 37

No. Heating would kill the enzymes created by the mould and create off aromas