(1) combination of progressive saccharification of starch and slow alcohol fermentation
(2) slow fermentation of low concentration of fermentable sugars to ethanol at a low temeprature. Even if the yeasts died, the enzymes are still in action.
(3) the yeasts used in rice wine brewing are characterized by high ethanol concentration tolerance. The high density of yeasts may be protected from damaging caused by high intensity of ethanol by adhering to the semi-solid state of fermenting mash, or by some substances existing in rice and wheat ( Qu is made from wheat) such as specially proteins, vitamine B which can absorb harmful fusel oils excreted by yeasts themselves.
(4) some unclear substnaces may exist in the fermenting mash which is good for yeast growth and fermentation.
The traditional process used Jiu Qu made by natural inoculated cultures of microorganisms. Fermentation was conducted in vats. The fed-batch fermentation, which means adding steamed rice was divided successively into several batches over a period of time was the most popular operating method. For example, in Han Dynasty, adding steamed rice was divided into 9 batches every third day. From Song Dynasty, adding batches of steamed rice was reduced to 3- 4 batches. The traditional brewing process was undertaking under non strict sterile conditions.
According to the methods for rice-cooling and operating procedures, the traditional brewing processes are subdivided into three basic forms given below.
(1) The steamed rice for main mash was cooled by drenching cold water through it,and this procedure was mainly used in traditional seed mash fermentation.
(2) The steamed rice for main fermentation mash was cooled by spreading it on bamboo mats.
(3) The steamed rice was added in successively several batches.
As described previuosly, the rice wines are classified into five types according to their sugar contents remaining in the final products. For making a particular type of rice wine, a process may be composed with several forms of brewing processes, For example, for making the YUAN HONG RICE WINE, a kind of dry type rice wine produced by Shaoxing in Zhejiang Province, The steamed rice for main fermentation mash is cooled by spreading it on bamboo mats, and the steamed rice used for seed mash is cooled by drenching fresh water through it.
Traditionally, the effective control of fermentation temperature was dependent on the stirring operating. It is especially important to choose the right moment for the first stirring. There were two operating procedures handed down from ancient times in Shaoxing. The most popular procedure accepted by the brewmasters in Shaoxing prefered to start the first stirring when the mash's temperature rise to above 35 ℃, and this is called " First Stirring at a High Temperature". This procedure will result in quick fermentation of sugar to ethanol, and the yeasts become old and feeble. More sugar remaining in the main mash. Another operating procedure is characterized by firstly stirring the main mash when the fermentation temperature rises to about 30 ℃, and alwasy the temperature is kept not to exceed 30 ℃. This is called "First stirring at a Low Temperature". This procedure will result in more sugar being converted to ethanol in slow fermentation. Anyhow, after the first stirring, the mash's temperature drops down notably. During the main fermentation, intermittent stirring is done according to the mash's temperature and room temperature. Temperature control pattern is given in Table 5.
|temperature of the mash||interval (h)|
|1st stirring||37-38 ℃||10 h after|
|mixing the indredients|
|2nd stirring||31-33 ℃||4-6|
|3 rd stirring||29-31 ℃||3-4|
|4th stirring||27-30 ℃||3-4|
wheat Xiao rice water rice Qu Qu 50 kg │ ↓ 8-10% 0.4-0.5% ↓ ├───→ steeping │ │ Washing ←──┤ ↓ │ │ Steeping ├────→ steaming │ │ ↓ │ │ │ Steaming ←──┤ │ │ ↓ │ ↓ │ │ Cooling by ←─┼────→ Cooling │ │ Drenching water │ by drenching water │ │ ↓ │ ↓ │ └──→ Seed mash │ │ │ ↓ │ │ │ Adding water──┘ │ │ ↓ │ │ a half 1st addition of 50 kg │ ├───────→ steamed rice ←──────┤ │ ↓ │ │ 1st stirring │ │ ↓ │ │ a falf 2ed addition of 25 kg │ └───────→ steamed rice ←──────┘ ↓ Further fermentation ( 70-80 days more) ↓ Squeezing→ spent grains ↓ Natural colorant → New rice wine ↓ Clarification ↓ Pasteurization ↓ Packing ↓ Rice wineFig 3.5.2 Fed-batch fermentation process
After the founding of the People's Republic of china, the wooden squeezers have been substituted by mechanical devices such as screw-type press and plate and frame filter-press.
In Qing Dynasty, a special heating device made of tin was recorded in << Tiao Ding Ji>>. The rice wine was heated by direct fire. The pasteurization conducted in the devices mentioned above was characterized by batchoperation.
The fresh rice wine is pasteurized at 85 ℃ to 90 ℃ , at this temperature, the rice wine is kept for about 5- 10 minutes, so as to kill the vegetative cells of microorganisms. Enzymes are also denatured, and proteins are coagulated. Heat treatment also has the function of facilitating maturation of rice wine.
During storage, rice wine is gradually matured, deepens color and diminishes harsh taste. After storage, rice wine is blended and is diluted to the appropriate alcohol content and sugar content. Finally, the rice wine is filtered, and packaged.
Packaging machines have been used widely in modern rice wine breweries since 1970's. The three forms of packaging rice wine are bottles, jugs (or pots) and plastic bags.
Modern rice wine brewing process is characterized by fermentation in big fermenting tanks and use of pure cultured yeasts, which will be described later.