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3.4 Preparation of Seed Mash Used for Ricewine Brewing
The seed mash (or called starter) for rice wine brewing is called "Jiu Mu", meaning "Mother of rice wine" ( or Mother Culture), and is partly analogus to yeast inoculum in beer brewing.The various seed mashes used for rice wine brewing can be classfied into three types according to the preparation processes: "Traditional seed mash" ("LING FANG Jiu Mu" in Chinese pronunciation) , "Pure Cultured Seed Mash" and Active Instant Dried Yeast (AIDY).
3.4.1 Traditional Seed Mash Preparation in Song Dynasty
Traditionally, the seed mash was from the fermenting young mash. In Song Dynasty, preparation of seed mash became a special process before the step of rice wine fermentation. The flowchart of preparation of seed mash described in << Beishang Jiujing>> ( published in about the begining of 12th century) is summrized as follows: Polished rice
↓
Steeping in hot and acidified liquid
↓
Steaming
↓
Spreading the steamed rice to cool it to a room temperature
↓
Mixed with Jiu Qu, acidified liquid, young mash or dried seed mash
↓
Fermentation for about 7 days
↓
Seed mash ready for rice wine brewing
So the seed mash preparation process had no considerable difference with main mash fermentation process.
3.4.2 Traditional Seed Mash Preparation Currently Used in Some Rice Wine Breweries
Generally, the processes for seed mash preparation is similar to rice wine fermentation. The particular features in seed mash preparation are using acidified liquid to adjust pH of fermenting mash, and the steamed rice is cooled by drenching fresh water through it. Nowdays, some riec wine breweries are still prepareing the traditional seed mash in modified processes which can be summerized as follows: Fresh water Polished rice
│ ↓
├────────→ Socking
│ ↓
│ Steaming
│ ↓
├───────→ Cooling the steamed rice
│ ↓ by drenching fresh water through it
│ Mixed with Xiao Qu ← Xiao Qu
│ ↓
│ Sacchrafication
│ ↓
└──────→ Mixed with wheat Jiu Qu and water ← wheat Jiu Qu
↓
Fermentation
↓
Stirring
↓
Secondary fermentation
↓
Seed mash
3.4.2.1 Ingredients for Preparation of Traditional Seed Mash
| ingredients | weight ( kg) | ||
|---|---|---|---|
| Glutinous rice | 125 | ||
| Wheat Jiu Qu | 19.5 | ||
| Xiao Qu | 0.187~0.25 | ( major microbes are Rhizopus spp. and yeasts) | |
| Water (including the water | 230 | ||
| absorbed in the cource of steeping | |||
| and steaming) | |||
3.4.2.2 Sacchrification and Fermentation
During the cource of saccharification, it is required to control the temperature of the mash at suitable level according to the wether condition. The Rhizopus spp. and yeasts exsiting in the Xiao Qu begin to multiply rapidly . Enzymes such as amylase and glucoamylase are excreted which hydrolyze the gelatinied starch to fermentable sugar. Usually, it takes 36-48 hours partly to hydrolyze the starch to a suitable extent, and sweet liquid will fiil the hollow part of the mash. The Rhizopus spp. has the ability of producing organic acids such as lactic acid and fumaric acid which lower down the pH of the mash. This favours the growth of yeasts and disencourages the growth of unwanted microorganisms, yeasts ferment reducing sugars to ethanol. When the sweet liquid has reached to a hieght of about four fifths of the seed mash, wheat Jiu Qu and fresh water can be added to the fermenting mash, then the mash being stirred throughly with wooden rack. Fresh air is incorporated to nourish the growing yeasts and JIU QU molds, carbon dioxide is expelled, and the mash from the vat's center is mixed with the cooler portions from the sides and bottom. When all the mash has been turned, its surface is smoothed and recovered. The vats covered with weaved straw mats is kept at a constant temperature. Yeasts multiply rapidly further after stirring.Stirring is repeated three times more, and keeping the temperature of the seed mash between 26-30 ℃. The stirring operation is the most important one that is always undertaken by experienced brewmasters. They judge the fermentation situation through smelling the odour, tasting the flavour, touching the seed mash and listening the sound from the fermenting mash. From the comprehensive information derived from a series of sensory evalution, they decide if it is the right time to stir the seed mash.Saccharification and fermentation of the seed mash lasts about 7 days, then the young seed mash is poured into jars with narrow neck for secondary fermentation. Much ethanol is produced after 20- 30 days (or may be three months ). Usually the ethanol content of the seed mash can reached up to 15%. The chemical compositions of the seed mash is given in table 1 below.
| Ethanol (v/v, %) | 15.44 |
|---|---|
| Total acids ( g/100 ml) | 0.3799 |
| Sugar ( g/100 ml, glucose) | 0.3936 |
| Starch ( g/100 ml) | 4.42 |
| pH | 3.9 |
3.4.3 Pure Cultivated Yeasts
The advanced techniques have been used in prepration of seed mash. These methods based on pure culture of yeast. One of these is called "Instant Seed Mash ", Scientists have isolated a few strains of yeasts from traditional seed mash and fermenting mash. These yeasts are taxonomically classified as members of the Saccharomyces cerevisiae group. The yeasts used for rice wine- making are characterized by the high concentration of sugar and ethanol tolerance. Although some wild yeast may be occur in wheat Jiu Qu and Xiao Qu, which are still absolutely necessary in rice wine fermentation, the dominant pure yeast cultures played a decisive part in rice wine brewing. These strains produce at least 15% (v/v) of ethanol in a fermenting mash containing 30 % (w/v) of starch.The instant seed mash is inoculated with yeast pure cultures instead of traditional Jiu Qu ( wheat Jiu Qu and XIAO QU) , so the possibility of infection caused by inaseptic operation by using XIAO QU is greatly reduced. Also, to adjust the pH of the seed mash to around 4.0-4.5, the lactic acid is added into the seed mash instead of adding acidified steeping water in which some unwanted microorganisms may exsit.
In current practice, a large yeast inoculum is prepared from the nutrient agar slant by a stepwise propagation of the yeast in successively larger volumes until an adequate inoculum is available to inoculate a plant fermenter. The basic ingredients for preparation of instant seed mash are similar to that of traditional seed mash, but water content may be higher than that of traditional seed mash. In order to suppress the proliferation of indigenous lactic acid bacteriua, lactic acid is added to the mash to regulate the pH of the mash to about 4.0, which favorate the yeast proliferation. Usually, a 1- 2 % (v/v) yeast inoculum is used, and the initial temperature of the mash is set at 26-30 ℃ according to the weather. When the temperature of the mash reaches above 31-32 ℃, stir the mash with pressed air. The cultivation time lasts about 1-2 days.
Another method of pure culture of yeast is currently used in rice wine breweries. Glucoamylse is added to the mash ( the ingredients are almost the same as those in the traditional seed mash but diluted with much water), then raise the temperature of the mash to 55- 60℃. Glucoamylase converts the geletinized starch in order to reduce sugar which is easily used by yeast culture. At this high temperature, wild yeasts and bacteria are destroied, so pure yeast cultures grow well.
