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3.5 Fermentation and Post-fermentation
The characteristics in rice wine brewing are of the use of several
types of "Jiu Qu" or "Qu". Wheat Qu is mainly a culture of Aspergillus
spp.; Xiao Qu is mainly a mixture culture of Rhizopus spp. and yeasts
grown on and within grounded rice meal. Jiu Qu, which is comparable
to malt used in beer brewing, is used for liquification and
saccharification of the starch contained in the rice grains. Using of
Qu (especially wheat Qu) also contributs to flavour substance
formation. Without using Qu, the rice wine may lose its typically
characteristic flavours and aroma.
For beer brewing, wort fermentation by yeasts takes place after
filtration and boiling of the mash. But for rice wine, the mash which
is called "Lao", is composed of geletinized starch contained in
steamed rice, Qu and seed mash, so the glucose is gradually
liberated from starch in steamed rice by the action of glucoamylase
and is fermented successively by yeast. This is called "parallel
fermentation" which combines progressive saccharification of starch
with slow alcohol fermentation at a low temeprature. This contributes to
considerable ethanol production, which can be as high as 20% (v/v) in
the final fermented mash.
The main mash is fermented without any special sterilization, and
the typical feature in rice wine brewing is also characterized by
the slow fermentation at a low temperature. The whole fermentation time
usually lasts about 3 months or even more than one year.
It is seldom seen that rice wine fermentation is conducted in such
a dense and mushy state that the rice grain vs water is in proportions
of about 1:2 ( for beer brewing, the malt vs water is in proportion of
1:4.3, and for whisky, about 1:5). This situation is called semi-solid
state fermentation. The dense fermenting mash is considered beneficial
in retaining large numbers of yeast cells in suspended solid or the
mash during the fermentation, which is one of the reasons that rice
wine contains as much as 20% (v/v) ethanol. For semi-solid fermentation,
because the mash easily floats on the surface, it is difficult for
the mash to send out the heat generated during the period of main
fermentation. The key to properly control of the fermentation
temperature is to stir the mash on time.
Among the fermented beverages produced around world, the ethanol
concentration in original rice wines mash produced by fermentation is
the highest, which amounts to above 20%( v/v). It is still difficult
to identify how many factors contributing to high concentration
ethanol being produced. The reasons often quoted are summerized as
(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
(4) some unclear substnaces may exist in the fermenting mash
which is good for yeast growth and fermentation.
We can roughly divide fermentation processes into two types:
traditional brewing process and modern brewing process. In this section,
we will first disccuss the rather simple methods of preparing rice
wines at home, then go on to discuss about the complete multi- step
process used by most commercial makers.
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
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
(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.
Fig 3.5.2-1 Traditional Fermentation vessle
In ancient times, brewmasters made their rice wines during the
cold months when the air and water is relatively free from
contaminating microorganisms. Late November is the best time for
brewing rice wines. In order to make rice wines during the warmer
parts of a year, because of difficulty in controlling the mash's
temperature, it was important to set the initial temperature of the
main mash as low as possible. Usually the main mash's temperature was
set according to the atmospheric temperature. The initial temperature
should not exceed above 28 ¡æ . Most breweries prefer to start
fermentation in a range of 24-26 ¡æ, in order to control the rate of
fermentation, so the maximun temperature of the fermenting mash would
be below 30-35¡æ.
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 ¡æ, 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 ¡æ, and alwasy the temperature is kept not to exceed
30 ¡æ. 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.
Fig. 3.5.2-2 Stirring
Fig. 3.5.2-3 Temperature Control in Traditional Brewing
Fig. 3.5.2-4 Temperature Control
Table 3.5 Temperature control during fermentation
( when room temperature is 0-10 ¡æ )
The main fermentation lasts about 1 week. When the main
fermentation is finished which is indicated by settling of the solid parts of
the mash, the mash is transferred to jars ( narrow neck jars) for
further fermentation ( secondary fermentation). In the narrow neck jars,
the mouth of the jar is sealed tightly so that air is kept from
contacting with the mash. In the case of big tank fermentation, the
main mash is transferred to secondary fermentation tanks. The ethanol
content of the main mash has already reached to about 13-14%, and most
yeasts are inhibited. Remaining starch and sugar are to be slowly
converted to ethanol during secondary fermentation. The mash is often
allowed to stand for about 70-80 days at a natural temperature; this
final ripening further improves the flavour and aroma. The ethanol
content rises by 2~4 % more.
| || temperature of the mash || interval (h)|
|1st stirring || 37-38 ¡æ || 10 h after|
| || mixing the indredients|
| 2nd stirring || 31-33 ¡æ || 4-6|
| 3 rd stirring || 29-31 ¡æ || 3-4|
| 4th stirring || 27-30 ¡æ || 3-4|
Fig. 3.5.2-4 Secondary Fermentation
Fed-batch fermentation processes have been practiced for at least
2000 years as described previously. This method is still widely used in
rice wine breweries. Usually the additions of steamed rice is carried
out successively in three batches. The flowchart of fed- batch
fermentation process is shown in Fig 4.
wheat Xiao rice water rice
Qu Qu 50 kg ©¦ ¡ý
8-10% 0.4-0.5% ¡ý ©À©¤©¤©¤¡ú steeping
©¦ ©¦ Washing ¡û©¤©¤©È ¡ý
©¦ ©¦ Steeping ©À©¤©¤©¤©¤¡ú steaming
©¦ ©¦ ¡ý ©¦
©¦ ©¦ Steaming ¡û©¤©¤©È
©¦ ©¦ ¡ý ©¦ ¡ý
©¦ ©¦ Cooling by ¡û©¤©à©¤©¤©¤©¤¡ú Cooling
©¦ ©¦ Drenching water ©¦ by drenching water
©¦ ©¦ ¡ý ©¦ ¡ý
©¦ ©¸©¤©¤¡ú Seed mash ©¦ ©¦
©¦ ¡ý ©¦ ©¦
©¦ Adding water©¤©¤©¼ ©¦
©¦ ¡ý ©¦
©¦ a half 1st addition of 50 kg ©¦
©À©¤©¤©¤©¤©¤©¤©¤¡ú steamed rice ¡û©¤©¤©¤©¤©¤©¤©È
©¦ ¡ý ©¦
©¦ 1st stirring ©¦
©¦ ¡ý ©¦
©¦ a falf 2ed addition of 25 kg ©¦
©¸©¤©¤©¤©¤©¤©¤©¤¡ú steamed rice ¡û©¤©¤©¤©¤©¤©¤©¼
( 70-80 days more)
Squeezing¡ú spent grains
Natural colorant ¡ú New rice wine
Fig 3.5.2 Fed-batch fermentation process
Since the rice wine mash is very dense and mushy, the specific
gravity differences of the mash between the solid part and the liquid
part are small. So the situations in squeezing of rice wine mash
differ greatly from mash filtration in beer manufacture. It is
difficult to obtain the liquid part ( rice wine) by filtration or
sedimentation. Combination of filtration and squeezig provides a
effective approach for separating the liquid part from the mash.
After secondary fermentation, the mash is to be squeezed to divide
into filtrate, rice wine, and solids, spent cake. Many types of filter
equipment had been used for this operation throughout the history. In
ancient times, the new rice wine was collected by making a hollow in
the upper surface of the fully- matured rice wine mash in a vat.
pressing a bamboo colander with conical bottom into the hollow, and
ladling out the liquid part (rice wine) that accumulated in it. In
Tang Dynasty, a type of wooden squeezer was invented, as recorded in
poems of that times, but the squeezer was not described in detail. A
wooden squeezer with more complicated structures was mentioned in < <
Bei San Jiu Jin>> published in 12th century. Technological innovations
of wooden squeezer continued from Song Dynasty to Qing Dynasty. The
large scale squeezer was made of a number of wooden frames where the
silk bags containing rice wine mash were held, and a pressing lid was
placed on the top surface of the frames. The wooden squeezer had a
structural stand with two sets of lever arms. Heavy stones exerted
pressure to one of the levers, and the level transfered the pressure
to the lip that pushed down the silk bags beneath it. A vat was used
for receiving the filtrate: rice wine.
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.
Fig.3.5.3-1 Wooden squeezer
The plate and frame filter-press is widely used in rice wine
breweries all over China. The rice wine mash is pumped into the frames,
and the liquid part is firstly filtered out through filter cloths. At
this stage, new rice wine can be obtained by filtration. By
incerasing the pressure gradually, the remaining liquid in the cakes is
squeezed out, and the cake is refermented for manufacturing distilled
spirits, or used for feed.
The slightly turbid rice wine is pumped to the fining tanks for
clarification. A kind of natural colorant called caramel is added to
the rice wine which is allowed to stand for 2-3 day's for clarification
until the clarified rice wine tastes smooth and sweet. The caramel
depens the color of rice wine.
As mentioned previously, Chinese firstly invented the heat
treatment method for pasteurization of alcoholic beverages in Tang
Dynasty ( 618-907 A.D.). The heating equipment used at ancient times
was very simple: a ceramic jar containing rice wine was surrounded by
chaocoal fire ( popular in Tang Dynasty); or a large cauldron topped
with a steamer. The rice wine was filled into a long necked jar which
was placed in a steamer. By heating indirectly, the rice wine in the
jar boiled ( Popular in Song Dynasty).
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.
Continuous pasteurization of rice wine was realized in 1950's.
Various types of heat exchangers have been used, such as the coiled pipe
cooler, double-pipe exchanger, shell and tube heat exchanger and plate
type exchanger, the latter being most effective.
The fresh rice wine is pasteurized at 85 ¡æ to 90 ¡æ , 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.
The pasteurized rice wine is stored in narow necked jars. The jars
are tightly sealed and are piled up one above another, and placed outside
buildings, letting to experience the rhythmic temperature changes of the
four seasons. Most rice wine starts its fermentation during the colder
months, undergoes most of its transformation during the warmer ones,
and is finally consumed about one year later. Thus the rice wine
experiences a rise and fall of temperature.
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.
Traditionally, the pasteurized rice wine when it is still hot is
packaged in sterilized ceramic jars which are considered good
for the further maturation of rice wine. The mouth of the jar is
immediately covered with sterilized lotus leaf and other sealing
materials and tied with string. the sealed mouth is further sealed
with specially treated mud mound that is cylinderly shaped, so
as to prevent contaminating microorganism from getting into the jars.
The so called "HUA DIAO JIU" made in Shaoxing, Zhejiang Province,
is packaged in jars outside of which are beautiful carving and
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.
Fig. 3.5.3-3 Hua Diao Jiu
Fig. 126.96.36.199 Traditional Tools for Rice Wine Brewing
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