Kōji

Question 1

List the components that are produced by kōji mould

Answer 1

Sugar, amino acids, peptides, vitamins, lipids (including fatty acids), subtle chestnut aromas and flavins

Question 2

How is sugar created and why is it needed?

Answer 2

It is created by the action of amylase enzymes on starch. It is needed as a source of energy for the yeast. No sugar means no fermentation

Question 3

How are the amino acids and peptides produced and why are they needed?

Answer 3

They are produced by the action of protease on proteins They are an important yeast nutrient, and they contribute towards the umami in a sake

Question 4

Name the three main amylases that are produced by kōji mould

Answer 4

Alpha-amylase, glucoamylase and alpha-glucosidase

Question 5

What are the difference between yellow, black and white kōji mould?

Answer 5

Yellow kōji mould are most commonly used in sake production, while black and white kōji mould produce high levels of citric acid and are not widely used in sake production.

Question 6

Name the two styles of kōji?

Answer 6

Sō-haze and tsuki-haze

Question 7

Sō-haze kōji has high levels of…

Answer 7

Enzymes, vitamins, sugars, amino acids, fatty acid, and peptides

Question 8

Why is sō-haze kōji used for faster and warmer fermentations?

Answer 8

A faster, warmer fermentation means that the yeast are more active. they therefore need more nutrients to sustain this higher level of activity. Higher levels of enzymes that are widely distributed throughout the kōji and therefore more easily accessible, as well as the higher levels of yeast nutrients secreted by the kōji mould, provide the required levels of nutrients

Question 9

Is the mould growth evenly distributed throughout the rice grains classified as tsuki-haze?

Answer 9

No, the mould growth is patchy and there are whole sections of the grains where there is no mould growth

Question 10

For the production of tsuki-haze kōji, do you need high or low levels of proteases?

Answer 10

Low ( due to minimising the amount of time the rice is in the temperature range where the production is at its highest)

Question 11

For the production of tsuki-haze kōji, do you need high or low levels of amylases (especially glucoamylase)

Answer 11

High (special strains of kōji mould are used so that these levels can be achieved despite the low levels of overall mould growth)

Question 12

For tsuki-haze, why are low levels of proteases required?

Answer 12

Low levels of proteases mean that fewer amino acids and peptides are produced which results in low umami in the final sake. If the levels of proteases are too high then this will result in umami levels that are also too high.

Question 13

For tsuki-haze, why are high levels of amylases required?

Answer 13

The brewer has to limit the mould growth to limit the production of fatty acids. Therefore, in order to ensure the yeast have access to enough sugars that limited amount of mould that is present needs to produce high levels of amylases.

Question 14

What are the seven stages of Kōji production in order?

Answer 14

1. Bringing in
2. Spreading the spores and initial mould growth
3. Re-breaking up
4. Mounding
5. Middle work
6. Final work
7. Sending out and drying

Question 15

When does bringing in happen?

Answer 15

Hour 0

Question 16

What temperature is rice cooled to during bringing in?

Answer 16

32-35

Question 17

What happens to the rice once it has been cooled during the bringing in stage?

Answer 17

It is spread out on a large shallow bed in the kōji room

Question 18

When does Speading the spores and initial mould growth happen?

Answer 18

Hours 1-3 until hours 10-12

Question 19

What happens to the temperature during spreading the spores and initial mould growth?

Answer 19

It slowly rises back to around 33-35°C (92-95°F)

Question 20

What is the aim of the stage of spreading the spores and initial mould growth?

Answer 20

To spread the correct amount of spores for the style of kōji being made and to encourage mould germination and growth

Question 21

What happens to the rice grains once they have been inoculated?

Answer 21

They are formed into a large pile and wrapped in blankets to retain warmth and moisture

Question 22

When does re-breaking up happen

Answer 22

Hours 10-12

Question 23

What happens to the temperature during spreading re-breaking up?

Answer 23

The temperature of the rice has risen to about 33°C (92°F) and is reduced to about 31°C (88°F); it then rises back up after a few hours to about 33°C (92°F)

Question 24

What is the aim of re-breaking up?

Answer 24

To ensure that the mould grows evenly throughout the mass of grains and to eliminate any hot spots

Question 25

What happens during re-breaking up?

Answer 25

The rice is unwrapped and spread out over the toko and all clumps are broken up. The grains are then reformed into a pile and wrapped up in blankets again.

Question 26

When does mounding happen?

Answer 26

Hours 20-23. This is the mid-point in the kōji production

Question 27

What happens to the temperature during mounding

Answer 27

It rises beyond 35°C (95°F).

Question 28

What is the aim of mounding

Answer 28

The aim of this stage is to start the focus on the distribution and level of mould growth within each individual grain of rice. The drying process will also start at this point.

Question 29

What happens during mounding?

Answer 29

The rice is unwrapped, and it is either spread out on the bed or it is moved to smaller containers, typically in less humid parts of the kōji room. These containers are boxes (medium sized) or trays (smallest). These containers are grains are regularly checked and moved to ensure even growth throughout the batch for the following 7-10 hours.

Question 30

When does middle work happen?

Answer 30

Hours 30-33

Question 31

What happens to the temperature during middle work?

Answer 31

The temperature falls then it rises again to about 38°C (100°F)

Question 32

What is the aim of this stage?

Answer 32

The aim is to release heat from the rice and to continue the drying process

Question 33

Why would a brewer making tsuki haze want to minimise the time spent in this stage?

Answer 33

The ideal temperature for protease production is 34-37°C (93-99°F) and their production needs to be restricted in the production of tsuki-haze.

Question 34

Why do brewers flatten out the rice and create patterns in the surface of the rice?

Answer 34

This increases the surface area of the rice and allows heat and moisture to escape more easily

Question 35

What would happen if the temperature got too high?

Answer 35

The kōji mould might die and create undesirable aromas

Question 36

When does final work happen?

Answer 36

Hours 36-38

Question 37

What happens to the temperature during final work?

Answer 37

The temperature remains above 38°C (100°F) but should not be allowed to exceed 43°C (110°F).

Question 38

What is the aim of final work?

Answer 38

The aim is to continue to release heat from the rice and to continue the drying process. There is a greater focus on drying.

Question 39

When does sending out and drying happen?

Answer 39

Hours 44-50

Question 40

What happens to the temperature during sending out and drying?

Answer 40

The temperature is reduced from about 38-45°C (100-113°F) to 10-15°C (50-59°F).

Question 41

What is the aim of this stage?

Answer 41

The aim is to stop the growth of the kōji mould by cooling the rice and drying it out.

Question 42

What often happens to the rice at this stage?

Answer 42

It is typically moved out of the kōji room to a cool dry part of the brewery. Fans are also used to help with the cooling and drying.