Chapter 12: The main fermentation (Moromi)

Question 1

What are the 3 aims of the brewer during fermentation?

Answer 1

-To avoid contamination or a fermentation stopping too early
-To achieve the correct balance between the 2 parallel processes of starch to sugar conversion and sugar to alcohol fermentation
-To achieve the desired aromas and textures for the style of sake

Question 2

What are the three stages of the fermentation? Explain

Answer 2

-Building: to set the levels of rice, water and koji and to avoid contamination
- 2nd: When most fermenting occurs, temp. needs to be controlled to achieve the correct balance between the processes and the correct style
-3rd: ending the ferment

Question 3

What are the main temperatures for fermentation and how long does it take?

Answer 3

-12-18 degrees
-21 to 28 days

Question 4

What about ginjo styles and fermentation?

Answer 4

-Different temperatures (lower): 10-12 degrees
-Take much longer (30-35 days)

Question 5

What happens with the speed of fermentation as alcohol concentration increases?

Answer 5

-Speed becomes slower
-At thelast stage, temperature is lowered to minimise the rate at which the yeast die and fermentation stops without further intervention

Question 6

What does the liquid contain when fermentation has ended?

Answer 6

-Slightly sweet liquid full of rice particles, yeast cells and koji debris

Question 7

Why is a sake fermentation complex compared to other alcoholic beverages?

Answer 7

-Because the sugar is being produced at the same time as it is being consumed
-Other beverages: producer starts with a fixed amount of sugar

Question 8

How are sake brewers able to achieve consistency from one batch to another?

Answer 8

-The relative proportions and timing of the ingrdients as they are added
-Temperature, speed and time

Question 9

Which fermentation vessels are often used, why? Name another type of vessel

Answer 9

-stainless steel
-easy to source, mantain and clean
-Sometimes Japanese cedar ‘kioke’ -> expensive, skilled workers, can add complexity

Question 10

What are the standard ratios of steamed rice, koji and water for the main fermentation?

Answer 10

-80 parts steamed rice
-20 parts koji
-130 parts water

Question 11

Why are the ingredients added in stages?

Answer 11

To ensure that the yeast population does not become too diluted and that there are always sufficient quantities of conversion enzymes from the koji

Question 12

Why does the shubo and early additions to the main fermentation contain higher proportions of koji?

Answer 12

To help get the fermentation off to a strong start

Question 13

For what type of sakes is the three stage addition suitable?

Answer 13

For all, from futsu-shu to daiginjo

Question 14

What happens during day 1 at the first addition? What is the Japanese name?

Answer 14

-Shubo is transferred to a large tank
-more water,koji and steamed rice is added until 1/6 of final total batch
-12-15 degrees which is good for yeast to multiply
-Name: Hatsu-zoe

Question 15

What happens at day 2 of the main fermentation? what is the Japanese name?

Answer 15

-Nothing is added to allow the number of yeast cells to multiply
-important to give the yeast population to build up to achieve a balanced fermentation
-temp. rises slightly as the yeast multiply
-Name= Odori

Question 16

What happens at day 3 of the main fermentation? What is the Japanese name?

Answer 16

-Water,koji,steamed rice is added (2/6) resulting in (3/6) of the total batch
-Name: Naka-zoe

Question 17

What happens at day 4 of the main fermentation? What is the Japanese name?

Answer 17

-Half of total batch is added to complete the 3 stages
-Temperature is lowered to reach the starting temperature of the main ferment (6-10 degrees)
-Some brewers replace some of the added water with ice to cool
-Name: Tome-Zoe

Question 18

The brewer needs to pay attention to…. regarding koji

Answer 18

-The amount and type of koji is correct to deliver the quantity of enzymes that is right for the target temp. and style of sake

Question 19

What happens if the measurements are not correct during day 4?

Answer 19

-Brewer will struggle to keep the fermentation to the required temperature
-If there are insufficient enzymes for a warmer fermentation, yeast will run out of sugar if the temp. target is achieved
-Excess enzymes for a lower temp. fermentation -> unfermented sugars leading to too sweet sake when target temp. is achieved

Question 20

How is liquefaction executed?

Answer 20

-With polished rice or rice that has been pulverised into a powder
-After steaming the rice is mechanically mixed with enzymes to allow the enzymes to break down the rice before it’s added to the fermentation

Question 21

Why would a brewer choose for liquefaction?

Answer 21

-Accelerates the fermentation process and helps to achieve more complete enzymatic digestion of the rice

Question 22

For which type of sakes is brewing by liquefaction used? Why?

Answer 22

-For inexpensive sake
-Faster production, higher yields per tonne of rice
-reduces dependence on koji
= cost effective

Question 23

What is required during the main fermentation if the temperature is between 16-18 degrees? why?

Answer 23

-A high quanitty of koji enzymes is needed to keep up with the demands of the yeast
-Because when temperature rises the creation of sugar increases more slowly than the rate at which the yeast consume the sugar

Question 24

What is required during the main fermentation if the temperature is between 8-12 degrees? why?

Answer 24

-The quantity of enzymes needs to be lower in order to prevent sugar production to become more than the yeast can consume

Question 25

What happens if the fermentation speed is slower than the rate of starch to sugar conversion?

Answer 25

Sake will become too sweet

Question 26

What can happen in extreme cases when the fermentation speed is slower than the rate of starch to sugar coversion? How can this be prevented?

Answer 26

-Inhibits further starch conversion, the higher sugar concentration can lead to higher levels of unpleasant volatile acidity
-Adding water, but excess of water can lead to dilution and a boring taste in final sake

Question 27

What is the temperature range for a rich junmai?

Answer 27

-16-18 degrees

Question 27

How can temperature be controlled?

Answer 27

-Traditionally= mushiro = woven mats around the tank to maintain a steady temperature
-Cooling? Ice in between the mat and the tank or heat exchangers that are submerged into the fermenting mass
-Modern: manage temp. with computer systems that control water circulation

Question 28

What is the main cause if fermentation speed races too far ahead of starch into sugar conversion?

Answer 28

-Enzyme production by the koji mould was insufficient
-The enzymatic conversion of protein into amino acids and peptides is often slower due to lower levels of the protease enzymes that are also created by the koji
-resulting sake = thin, low umami due to lower concentration of amino acids and peptides

Question 29

What is the temperature range of daiginjo?

Answer 29

-10-12 degrees

Question 30

Why is temperature so important during main fermentation?

Answer 30

If the temperature is wrong it is not possible to make the required style of sake because the desires aromas and flavours are not created

Question 31

What is pyruvic acid? What happens if it remains?

Answer 31

-Occurs partially through the steps by which yeast convert glucose into ethanol
-If brewer stops fermentation too early, the remaining uncoverted pyruvic acid can cause unpleasant sour aroma’s of be converted into acetaldehyde that can give undesirable wood-like aromas

Question 32

Why is temperature generally lowered at the late stage of fermentation?

Answer 32

-High temperatures and high alcohol concentration would create stressful conditions for yeast and they can die
-Dying yeast create undesirable taste and aroma
-low temperature = stops yeast activity and ends the production of alcohol

Question 33

What are the reasons to ferment high-umami styles of sake at the top end of the temp. range, use rice with higher polishing ratio (>70%) and so-haze koji?

Answer 33

-Rice with higher polishing ratio contains higher levels of protein which can be broken down by koji proteases into amino acids that increase the umami taste
-so-haze koji has higher levels of protease and amylase enzymes: needed to ensure that the yeast have enough sugar and other nutrients during more faster fermentation

Question 34

Higher temperatures lead to…
For which styles is this suitable?

Answer 34

-Yeast population growing rapidly, higher acid production, lower aroma production
-Higher concentrations of amino acids and peptides which means richer taste
-Suitable for futsu-shu and junmai

Question 35

What are the reasons to ferment ginjo styles at low temperature using rice with lower polishing ratio and tsuki haze koji?

Answer 35

-lower polishing ratio and tsuki haze koji provide a slow release of a low total level of amino acid nutrients and sugars = limits growth of yeast
-slow fermentation, low production of acids and low levels of proteins = light and smooth tastes and textures

Question 36

What does low nutrient and low temperature fermentation conditions enhance?

Answer 36

-The production of esters and low temperatures reduce the loss of these esters by evaporation
-cold temp + shortage of nitrogen put yeast under stress

Question 37

How do yeast create these esters?

Answer 37

-complex sequence of enzymatic reactions, yeast combine the various alcohols with an acetyl compound (derivative of acetic acid), the caproyl compound or other chemical groups to produce highly fruity of floral aromatic compounds (esters)

Question 38

What are the most notable esters in ginjo styles?

Answer 38

-Isoamyl acetate (aromas of banana)
-ethyl caproate (green apple/melon)

Question 39

Why can brewers only make small adjustments regarding temperature with ginjo styles?

Answer 39

-the temperature is already close to the temperature below which yeast stop working so only small adjustments can be made
-Important to polish as much of the nutrient rich outer parts of the rice grains when making ginjo, otherwise create undesirable flavours, acidity and a coarse texture

Question 40

Why do brewers need a low temperature for ginjo styles?

Answer 40

-To avoid losing volatile ginjo aromas and to limit enzymatic digestion of the rice, keeping the texture fine and smooth
-Important to manage the growth of koji for ginjo sakes

Question 41

Why are there lower levels of other flavour and texture components such as amino acids with ginjo?

Answer 41

-During long fermentations at lower temperatures, the enzymatic digestion of the rice is less complete, leaving more rice solids in the tank creating a very smooth and clean delicate texture

Question 42

It is believed thst the ideal size of brewing ginjo styles is between… of polished rice per batch and … of water

Answer 42

-600-1500 kg rice
-800-2000 liter water
= 720-1800 liter sake

Question 43

What is the size of the tank voor honjozo/junmai?

Answer 43

up to double compared to ginjo

Question 44

Why are the yields for honjozo higher than ginjo?

Answer 44

due to small amount of jozo alcohol added

Question 45

Why is there a greater liquid extraction with honjozo?

Answer 45

Due to higher temperatures and more active koji enzymes = more complete breaking up of the rice

Question 46

How big are batches for futsu-shu? What is the main reason?

Answer 46

-20-30 times bigger than honjozo
-much lower production costs

Question 47

How much sake can be made from how many kg rice? State for ginjo,honjozo and futsu-shu

Answer 47

• 1 kg of polished rice = 2.5 liter of junmai ginjo
• 1 kg of rice = 2.6 liter of honjozo
  -1 kg of rice = 5 liter of futsu-shu (due to large amounts of permitted addition of jozo alcohol)