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The Jiuqu is roughly equivanlent to the English word malt and yeast, but is somewhat wider in scope, since it may include filamentous fungi as well as bacteria, and connotes the starter or inoculum used to initiate various kinds of fermentations. They are croase enzyme preparation.
The Jiuqu is traditionally prepared by natural inoculation of molds, bacteria, and yeasts and their growth on the grains. In a practical sence, mouds, yeasts and bacteria naturally present in the environment and on equipments serve as inocula for preparing Qu. Moistened wheat flour or rice flour are suitable substrates for their growth. During the growth of these microorganisms, a lots of hydrolysing enzymes are excreted and immobilized on the grains which are ready to use as sources of amylase for conversion of starch to sugar, followed by conversion of sugar to ethanol by yeasts.
For alcoholic beverages made from cereals all over the world, we might roughly classify the brewing technology into two types: One is the utilization of malted cereals which supply both raw materials and enzymes; the other is the utilization of molded cereals which offer microbial enzymes and microbial cells or spores.
Since Sang Dynasty (16th century B.C.- 11th century B.C.), most of the alcoholic beverages have been brewed by using Jiuqu. The characteristic features in the manufacture of Chines alcoholic beverages ( rice wines, Chinese spirits, etc.) are the use of Jiuqus.
The important enzymes and their functions can summarized as follows:
amylase: for degradation of starch to dextrin;
amyloglucosidase: for saccharification of the dextrin to glucose, maltose and other fermentable sugars;
protease and lipase:decomposition of proteins and fast contained in the raw materials.
the enzymes for ethanol production ( so called Zymases).
(2) severed as a supplier of varieties of microorganisms:
Traditionally, the microorganisms involeved in rice wine-making exsist naturally in the raw materials, the equipmemt, and the environment where the Jiuqu is manufactured. The preparation processes have the characterized features in using indigenous flora, or during the whole process foreign infections are not absolutely prohibited. Of course, the microorganisms may not be present at the same time, frequently a succession is involved as the environment changes due to the excretion of metabolotes. Quality alcoholic beverages produced by the traditional indigenous flora will probably never be equalled by the use of pure cultures.
(3) severed as a source of flavour and aroma substances:
(4) servred as raw materials:
According to their raw materials, Jiuqu may be roughly divided into three categories as follows. The customly classifying systems are also given below. As there are no corresponding English terms for all of them, we here describe them in Chinese alphabetic writings.
"Mi Qu" or "Xiao Qu" ( or "White Jiuqu" ): mainly used in rice wine brewing, and Chinese spirits made from rice. The Xiao Qu is made from rice, and the dimension of the Jiuqu is small;
"Yao Qu" ( in which Chinese herbs are added, it is made from rice);
"Bai Qu" or "Bai Yao" ( colored in white, made from rice);
"Hong Qu" ( red rice; or red Jiuqu; Angkak, made by innoculating Monascus spp.); it is used as a colorant in foods, and used for rice wines.
"Hei Qu" ( colored in black, made from rice, Aspergillus niger grows on it);
"Wu Yi Hong Qu" ( colored in red mixed with black, made from rice, Aspergillus niger and Monascus spp. are grown) .
"Da Qu" ( big Jiuqu, the dimension of it is big, and is made from wheat): it is used for Chinese spirit production, it was originated from Mai Qu.
According to the methods of processing the raw materials, Mai Qu may be called:
"Shu Mai Qu" ( made from steamed or roasted wheat),;
"Seng Mai Qu" ( made from fresh wheat);
"Bing Qu" (flat pancake-like), Zhuang Qu ( block-like);
"Dou Qu" (the bean or pea Jiuqu are mixed with wheat or rice flour,
it can be used for rice wine or spirits production).
. According to their manufacture procedures, Jiuqu may subdivided into:
According to the inoculation methods natural inoculation with wild species, or artificial inoculation
According to the microorganism involved indigenous flora, pure culture or mixed cultures; Aspergillus flavour; Aspergillus niger; Aspergillus oryzae; Monascu spp; etc.
According to the incubation temperature: High temperature incubated Jiuqu; medium temperature incubated Jiuqu
According to incubation conditions: aeratedly incubated thick-layer Jiuqu; thin-layer incubated Jiuqu
Jiuqu incubated in hanging over state