Sake falls within that group of alcoholic wines brewed using rice as the carbohydrate source. It is Japanese in origin with the key features of utilizing (i) particular rice varieties; (ii) only highly polished rice (unlike other rice wines from other cultures; the level of polishing desired removes between 40 to 60 % of the outer kernel) as this minimizes the flavours imparted by any retention of bran and non-starch components of raw rice; (iii) a hydrolysation stage (kome koji) where sugars are released by the breakdown of rice starch by the enzymatic action via a fungus.

The rice variety used is Oryza sativa subsp. japonica. This is a short-grain variety with a higher amylopectin content than long-grain rice (the other component of rice starch is amylose) which gives rise to a sticky characteristic when cooked.
 

The short-grain Japonica rice which I used (labelled as bento rice)
 

Starches are polymers of glucose units. They are only fermentable after they are saccharified to release fermentable sugars. Kome koji fungi are used for starch saccharification because they produce amylases such as alpha-amylase and glucoamylase.  Amylopectin is more difficult to hydrolyze by kome-koji fungi because of its alpha 1-6 linkages (between glucose molecules in starch) are only susceptible to glucoamylase. Hydrolysis by glucoamylase (to release monomers of glucose) is slower than via alpha-amylase (acting on alpha 1,4 linkages in amylose to release short chain amylose or dextrins or oligosaccharides) and because glucoamylase is an exo-amylase (acting only on chain ends) whereas alpha-amylase is an endo-amylase (acting from within polymer chains).

Koji kin is the fungal agent used for hydrolysis. It is typically Aspergillus oryzae.
 

A conidiophore of Aspergillus oryzae

 

MATERIALS AND METHOD

GENERAL PRECAUTION
You are making a food product which is consumed without cooking.
Exercise maximum hygiene/sanitation in all your procedures and disinfect equipment prior to usage.

Making kome koji (saccharification by a live fungal agent to produce hydrolysed rice starch)

Starches are stored in crystalline granules. These need to be "hydrated" in a step called "gelatinization" where polymeric starch is brought into solution and thus becomes amenable to further chemical and physical transformation e.g. via enzymatic hydrolysis. Rice starches gelatinize in the temperature range 68 - 78 degrees centigrade.
 

• Take 240 g of polished short-grain rice and wash thoroughly until the water runs clear.
  This will remove any remnants from outer rice layers and also prevent the steamed rice granules from tending to stick together.
  
  240 g of resulting kome koji is the quantity which when added to 1 kg of cooked rice and 1 L of water will be the fermentation mash (see below).
   

• Steam the rice until the grains are plump and soft.
  This is the arrangement which I used:

A large sieve, a large pot and a lid to cover. This was around halfway through a 2 h steaming process
 

• Spread the steamed rice onto a sterilized tray and let the steamed rice cool down (to at least 30 degrees centigrade).
   

• For my source of the fungus, I used commercially available kome koji (what is being made in this step viz. steamed rice upon which Apergillus oryzae is cultured).
  
  This is the kome koji which I bought online:

Koji kin available online
 

• Finely  grind 5 - 10 g of the kome Koji .
   

• Mix the ground kome koji well into the rice, cover (not airtight) and leave in a warm corner of a room for the fungus to grow throughout the rice. In growing on the rice, hydrolytic amylolytic enzymes released will break down starch into fermentable sugars for the next stage of the process.
  
  Check the inoculated rice regularly while taking care not to introduce contaminants into the mix; mix the rice with a sterilized utensil at these points to ensure even development of the fungus.
   

• The process may be stopped after some 30 - 48 h if the culture progressed optimally.
  
  You now have kome koji for the alcoholic fermentation stage.
   

• The property of kome koji which is desired for the sake process is its content of amylolytic ezymes such as alpha-amylase and glucoamylase which are required to saccharify rice substrate which will be added in the fermentation stage. These enzymes accumulate in the kome koji as the koji kin fungus grows throughout the rice during the preparation of kome koji. Without the agency of these enzymes, the starches in the added rice substrate will not be fermentable by the yeast cells added together with the rice.

kome koji ready to use after a two-day incubation
 

Preparing the yeast inoculum

Some 36 h before needing to use it, start making the yeast inoculum:

• Take 10 g of ground kome koji and add 100 mL of sterilized water at room temperature to a sterilized container with a lid.
   

• Add a few grams of dried yeast and set aside in a warm corner of a room for the yeast to multiply.
  I used a wine yeast strain which was bought online but you can experiment with various types including sake strains if you can find them (sake strains generally have higher alcohol tolerance).
   

• The inoculum will be ready to use after 24 h.

The yeast Saccharomyces cervesiae used in ethanolic fermentations
 

The alcoholic fermentation (sake stage)

It is now time to combine the kome koji with more rice substrate.

• Cook 400 g of short-grain rice until soft (thus ensuring that all the rice starch granules in the kernels are gelatinized).
  Allow it to cool to at least 30 degree centigrade.
   

• In a suitably-sized container with a tight lid, combine:
   

  • the cooked rice;

  • 135 g of kome koji previously prepared;

  • 1.5 L of boiled water allowed to cool to at least 30 degrees centigrade;

  • 100 mL of the yeast inoculum previously prepared.
     

• Stir well with a sterilized utensil, close the container and set aside in a cool room for 10 to 14 days.
  
  Through the days, the saccharolytic enzymes in kome koji will cleave polymeric starch in the cooked rice to produce fermentable sugars and the yeast in the inoculum will in turn grow and convert those sugars into ethanol.

The brew at the beginning of Day 2
 

• Check the brew each day and allow gas build up to vent if you do not have a water trap on the lid of the brew container ("burp" the vessel).
  
  You should notice bubbling (CO₂ evolution) from the first day.
   

• When active bubbling has ceased, your brew is ready.
  
  Fermentation will typically cease when the substrate runs out or when the ethanol concentration has gone higher than what the yeast cells can tolerate. The two are related since high alcohol content can only be reached if the starch has been well cleaved and there was a sufficient amount of the latter supplied at the start of the brew. In home fermentations such as described here, starch substrate is probably in excess. Given that sufficient fermentable sugars are released during the brew, fermentation probably ends due to the yeast's alcohol tolerance being exceeded.

The brew at the end of Day 7
Active bubbling has stopped; quantity of large particulates have reduced; clearer brew at the top
 

Clarification

At the end of fermentation, there will be a lot of rice and yeast matter in your brew and so you may wish to have a more clarified product. You can:

• Pour the fermented brew mash through a fine sieve to remove coarse matter.
   

• Allow the larger particles in the sieved brew to settle by placing it in a refrigerator over a few days. This is called "cold-crashing". Decant the clearer brew at the top and it will be ready for drinking.
   

• You choose to further clarify the product by passing it through a cloth or finer filter matrix.
   

• Sake can be drunk fresh in cloudy or clear form according to preference as is the choice of it being cold or warmed up.
   

• For storage, the fresh sake should be pasteurized by holding it at 65 degrees centigrade for at least 30 minutes.

Left: Day 7 brew after sieve-filtration and cold-crashing overnight in the refrigerator
Right: Cold, clear sake decanted from the top of the cold-crashed brew on the left.

 

ENJOY YOUR EFFORTS!