Fermentation Flashcards
What type of yeast is strain #7?
Reliable fermenters
What type of yeast is strain #6?
Reliable fermenters
What type of yeast is strain #14
Low acid ginjō yeast
What type of yeast is strain #1801
Low acid ginjō yeast
What type of yeast is strain #9
Early ginjō yeast
What type of yeast is strain #11
Reliable fermenters
What type of yeast is strain #10
Early ginjō yeast
What does ‘01’ at the end of a yeast number indicate?
It is a low-foaming yeast
Why do brewers prefer to use low-foaming yeast?
Foaming sake yeast create a thick layer of a sticky foam on the top of the fermenting liquid that can take up as much as half of the volume of a fermentation tank. This foam leaves a residue that takes a lot of time to clean. Low foaming yeast reduce the time and effort involved in cleaning and allow the brewer to fill the tanks fuller and therefore make more efficient use of their fermenters. There is also no risk of overflow which could contaminate other tanks
In what format are most purchased yeast supplied to breweries in Japan?
Glass ampoules
How does the temperature affect the behaviour of yeast?
The warmer it becomes the faster the yeast work. The colder it is the slower they ferment. At around 3-5C (37-41F) they stop fermenting altogether.
How does the cold help a brewer?
Microorganisms that could spoil the fermentation starter are less active and therefore present a reduced risk at low temperatures
What can a brewer use to cool a fermentation starter
Daki, pipes that circulate cold water, insulation or ice wrapped around the outside of the vessel
What equipment can be used to warm a fermentation starter should it be too cold?
Daki, heat jackets, heat lamps or foot warmers
How big is the fermentation starter compared to a main fermentation batch?
The starter is typically 6-10% of the size of the main fermentation batch
Why is an acidic environment important for a fermentation stater?
Sake yeast are able to tolerate an acidic environment whereas other microorganisms that might spoil the fermentation starter struggle in this environment. This gives the yeast a competitive advantage in the fight to form a dominant population and ‘gain control’ of the sugar and other yeast nutrients.
Is the percentage of kōji used in the fermentation starter different to the percentage of kōji in a main fermentation batch?
Yes. Typically, 30-33% of a fermentation starter is kōji, whereas kōji makes up 20-23% of the main fermentation
Describe the sokujō-moto fermentation starter method.
Describe the kimoto fermentation starter method.
Describe the yamahai fermentation starter method
How long does sokujō-moto typically take to complete?
14 days
What is added at the start of sokujō-moto?
Water and kōji
What is the temperature at the start of sokujō-moto?
18–25°C (38–77°F).
What is added next after water and kōji in sokujō-moto?
Lactic acid, steamed rice and yeast
What is the temperature on day 2 of sokujō-moto?
10°C (50°F).
What happens to the temperature over the course of sokujō-moto?
It gradually rises to around 20–23°C (68–73°F) before being chilled to 7°C (45°F) on day 14.
How does middle temperature sokujō-moto differ from standard sokujō-moto?
The starter is not chilled on day 2 and stays at higher temperatures throughout. This method is completed in half the time.
How does kō-on tōka-moto differ from standard sokujō-moto?
The temperature starts at 55–60°C (131–140°F) which sterilises the mixture and speeds up the starch to sugar conversion. After 6–8 hours, the mix is chilled to 40°C (104°F) and lactic acid is added. Cooling continues and the yeast are added when the temperature is 25–30°C (77–86°F). The temperature is slowly lowered to 18°C (64°F) and the shubo is completed in seven days.
What is mixed together on day one of kimoto and what is the temperature?
Steamed rice, kōji and water at a temperature of 6–7°C (43–45°F).
What starts on day 2 of kimoto?
The rhythmic pounding of the mixture with poles
Why is the pounding necessary in kimoto?
It breaks up the rice and increases the amount of contact between the rice starch and the kōji enzymes
What microorganisms grow during the first 14 days of kimoto and in what order do they appear?
Nitrate-reducing bacteria appear followed by lactic acid bacteria
Why are these microorganisms important in kimoto?
They produce acids which drops the pH of the starter. This ultimately helps the yeast to thrive.
Can yeast tolerate nitrous acid?
No, this is why nitrate-reducing bacteria must die and the levels of nitrous acid fall before the yeast are introduced
When are the yeast active during kimoto?
From about day 14 to the end at around 22-23
How does yamahai differ from kimoto?
The ratio of water to rice is also slightly higher. On day one, kōji and water are mixed at a higher temperature (8–9°C / 46–48°F) to extract enzymes. Then, steamed rice is added and the whole mixture is mixed vigorously. On day one this involves pumping over and after that, it is stirred with a pole. After this, the process is the same as kimoto.
What does parallel fermentation mean?
It means that the starch is converted to sugar at the same time the sugar is converted to alcohol. These fermentation require careful management if they are to be successful.
During the main fermentation, what is added on day one and how much of the final volume of the main fermentation batch is it?
The fermentation starter is mixed with more kōji, steamed rice and water. The first addition makes up a sixth of the final volume
During the main fermentation, what is added on day two and how much of the final volume of the main fermentation batch is it?
Nothing
During the main fermentation, what is added on day three and how much of the final volume of the main fermentation batch is it?
More kōji, steamed rice and water. The second addition makes up a third of the final volume. At the end of day three the half of the batch is in the fermentation vessel
During the main fermentation, what is added on day four and how much of the final volume of the main fermentation batch is it?
More kōji, steamed rice and water. The third addition makes up a half of the final volume. At the end of day four the fermentation batch is complete.
Why do sake brewers go to all this effort when making up a fermentation batch?
Sake brewers need a healthy yeast population and so they need to avoid spoilage microorganisms. However, they cannot rely on certain methods to protect their yeast, such as preservatives like SO2. These preservatives combat spoilage organisms or high acid, which spoilage organisms struggle to thrive in. Therefore SO2 wouldn’t work and adding more acid (in a similar way to the fermentation starter) would create a sake that is too high in acidity.
Building the fermentation batch in stages means the yeast only have to dominate a small amount of extra liquid, which they can do quickly. This in turn prevents spoilage organisms from growing. If the ingredients were all added together, the yeast would take longer to grow into the whole mass of liquid and this would allow spoilage organisms to establish themselves too.
Which style of sake does relatively low levels of proteases belong to?
Ginjō style
Which style of sake does high levels of amino acids and peptides belong to?
Rich, high umami style
Which style of sake does low polishing ratios belong to?
Ginjō style
Which style of sake does high levels of enzymes belong to?
Rich, high umami style
Which style of sake does tsuki-haze kōji belong to?
Ginjō style
Which style of sake does low levels of amino acids and peptides belong to?
Ginjō style
Which style of sake does duration 30-35 days belong to?
Ginjō style
Which style of sake does relatively higher levels of amylases, especially glucoamylases belong to?
Ginjō style
Which style of sake does high levels of nutrients support faster fermentation belong to?
Rich, high umami style
Which style of sake does high polishing ratios belong to?
Rich, high umami style
Which style of sake does fermentation temperature close to 18C (64F) belong to?
Rich, high umami style
Which style of sake does fermentation temperature close to 10-12C (46-54F) belong to?
Ginjō style
Which type of sake does duration 21-28 days belong to?
Rich, high umami style
which type of sake does low total levels of enzymes belong to?
Ginjō style
Which type of sake does Sō-haze kōji belong to?
Rich, high umami style
There are two main ways a brewer can ensure their fermentation remains balanced. What are they?
- Temperature control.
- Ensuring the correct amount of enzymes are present from the style of fermentation
What is the principal challenge low levels of mould growth causes the brewer with regards to sugar production during fermentation?
Low levels of mould growth mean low levels of enzymes. Therefore, there is a risk that the yeast run out of sugar.
How does the brewer prevent their yeast from running out of sugar when using tsuki-haze kōji?
The fermentation is conducted at low temperatures which mean that the yeast need less sugar at any given time. Brewer also look to maximise the production of amylases (especially glucoamylase) when they make tsuki-haze kōji by keeping the temperatures post-mounding high.
Why are low levels of amino acids and peptides necessary for ginjō fermentations?
This stresses the yeast and as a result they produce greater quantities of higher alcohols which are precursors to ginjō aromas. All yeast will do this, ginjō yeast produce much greater quantities of these alcohols.
How does a brewer ensure that there are low levels of amino acids and peptides?
They need to ensure that the kōji has relatively low levels of proteases, which create these amino acids and peptides from proteins. This is achieved by minimising the amount of time kōji spends in the temperature range 34-37C (93-99F) which is the ideal temperature for proteases production
