The document discusses the industrial production process of ethyl alcohol. There are four main steps: [1] inoculum production using yeast strains, [2] preparation of the fermentation medium using molasses and other nutrients, [3] batch fermentation in large tanks under controlled temperature and pH conditions, [4] harvest and recovery of ethanol through distillation. The ethanol produced is then purified through fractional distillation and used widely as a solvent, fuel additive, and in various industrial products. Proper cultivation of yeast strains and maintenance of fermentation conditions are important to optimize ethanol yield from the process.

1. By
Mr. Abhirup Ganguli
Asst. Professor, Dept. of Biotechnology
Swami Vivekananda Institute of Modern
Sciences
Industrial Production of Alcohol

2. Introduction to the Production
Process of Ethyl Alcohol:
 Ethyl alcohol has been produced on large
scale for centuries.
 However, much study could not be
accomplished because of hazards on
human consumption.
 In 1865 Alcohol Act was passed thereby
free sale of alcohol after its denaturing by
adding methylated spirit was allowed.
 Early production was primarily used for
human consumption.

3.  But today, apart from being used for human
consumption, it is also used as universal
solvent and as chemical raw material for
the production of other industrial products.
 Along with gasoline it is also used as motor
fuel. Because of the above utilities the
demand for alcohol increased enormously
today, which lead to establishment of many
distilleries throughout the world.
 Ethyl alcohol is produced, besides yeasts,
by large number of bacteria and fungi (table
3.2).

5.  The biochemical synthesis of alcohol by
different microorganisms is depicted in Fig.
3.3.

6.  Similarly, besides use of molasses,
lignocelluloses can also be used as a
sustainable substratum (table 3.3).

7.  However, apart from fermentative production it is
also produced by chemical processes primarily by
catalytic hydration of ethylene.
 Chemical conversion of lignocellulose by different
fermentations are shown in table 3.5.

8.  The whole process of bioconversion of lignocellulose
into valuable sugars and other substances are
illustrated in Fig. 3.5.

9. Fermentative Production of Ethyl
Alcohol:
On commercial scale ethyl alcohol
production process
consists of four steps.
They are:
 (i) Inoculum production,
 (ii) Production medium,
 (iii) Fermentation process, and
 (iv) Harvest and recovery

10. (i) Production of Inoculum:
 Both yeast and bacteria are used for the
production of ethyl alcohol.
 Among the bacteria the most widely used
organism is Zymomonas mobilis and among
the yeasts Saccharomyces cerevisiae,
Saccharomyces carlsbergensis, certain
species of Candida and Mucor are also used,
depending upon the raw materials available
for ethanol production.
 But high yielding and alcohol tolerant strains
of S.cerevisiae are usually employed.

11.  Details of process for production of ethyl alcohol from
different substrates are depicted in Fig. 3.3.
 High yielding strains of yeast are generally used for
commercial production of ethanol.
 These are developed by genetic selection.
The strain of yeast that may be used for the
industrial
production should possess the following
characters:
1. It should possess uniform and stable biochemical
properties.
2. The ability to ferment a broad range of carbohydrate
substrates rapidly.
3. It should yield large quantities of ethanol.

12. 6. It should be tolerant to higher concentration of
alcohol.
7. It should possess high temperature tolerance.
8. High cell viability for repeated recycling.
9. Appropriate flocculation and sedimentation
characteristics to facilitate cell recycle.
 However, the choice of microorganism employed
in large scale ethanol production depends upon
the type of raw material used.
 For example S. cerevisiae is employed when
starch or maltose is used as raw material, when
whey or sulphite waste liquor is used as raw
material Candida utilis and C. albicans
respectively is employed in the fermentation

13. Inoculum Production Process:
 A suitable pure strain of yeast is inoculated into
a test tube containing approximately 10 ml of
sterile medium.
 It is incubated at 28°C to 30°C till sufficient
growth of yeast takes place.
 The medium employed for the preparation of
inoculum and the fermentation process is
generally similar.
1. After sufficient growth of the yeast occurs, the
culture from the test tube is transferred to a flask
containing approximately 200 ml of the medium.
 The flask is incubated at 28°C to 30°C until

14. 2. The fully-grown culture from the flask is
transferred to a glass container containing 4
liters of sterile medium and is incubated at 28°
to 30°C till sufficient growth takes place.
3. The culture from the glass container is finally
transferred to a small seed tank containing 40
gallons of sterile medium. Then seed tank is to
be near the fermentation tank. The culture
broth after incubation will be ready for
inoculating into the production tank.
 A large amount of yeast culture ranging from 8
to 10% volume of inoculum is required in the
industrial production of ethanol.

15.  To achieve rapid growth of yeast and large amount
of cell mass, high degree of aeration and agitation
of the medium is required.
 The pH and temperature are adjusted at 4.8 and
28° to 30° C respectively during the growth of the
yeast.
(ii) Preparation of Medium:
 Composition of fermentation medium plays an
important role in achieving optimum yield of
ethanol.
 It should be prepared in such a way that it
contains all the sources of materials that promote
optimum growth of yeast and optimum yield of
ethanol.

16. (a) Carbon Source:
 Different varieties of carbohydrates which are
produced as waste products in agricultural
industries can be used as carbon source.
They are grouped into the following
categories
depending upon their chemical nature:
1. Starchy material – potato starch, cereals like
oats, wheat flour and corn starch.
2. Saccharide material – fruit juice, whey,
molasses and hydrol.
3. Cellulose material – sulphite waste liquor,
lignocellulose.

17.  Molasses is generally used as the main carbon
source in the preparation of fermentation medium.
 However, cane molasses is used in India because
of its availability in large quantities from sugar
industries.
 The raw material indicated above, require
pretreatment in the form of saccharification.
 They are put to hydrolysis during saccharification
due to which easily fermentable sugars like
maltose and glucose are formed.
 The optimum sugar concentration should be
maintained between 10 to 18% in the
fermentation medium.
 If beet molasses are used, biotin should be added

18.  If cane molasses is used as a carbon source, its
sucrose concentration should be reduced to 10%
by the addition of distilled water which is called a
Wort.
 Higher sucrose concentration affects the growth of
yeast adversely, while lower sucrose concentration
makes the fermentation process uneconomical.
 In recent times, lignocelluloses as source of
carbon proved to be more economical and
sustainable.
 Most of the plants after death are subjected to
decomposition releasing fermentable sugars.
 Large amount of lignocellulose out of waste
agricultural products can be converted to sugars
by enzymatic hydrolysis.

19. Composition of plant lignocellulosic materials on
hydrolysis are
depicted in table 3.4.

20.  Integrated process of conversion of lignocellulose
wastes into value added saccharides is presented in
Fig. 3.5 and ethanol production from different
substrates is depicted in Fig. 3.4.

21. (b) Nitrogen Source:
 Variety of inorganic and organic nitrogenous
compounds may be used as nitrogen source in the
medium preparation.
 Ammonium sulphate is generally used as nitrogen
source.
 Generally 0.15 g of ammonium sulphate is added to
2.5 gallons of molasses.
 The concentration of nitrogen should be carefully
maintained as indicated above. Excess nitrogen
promotes rapid growth of yeast cells and decreased
production of ethanol.
(c) Growth Factors:
 As most varieties of molasses, for example cane
molasses, contain suitable concentration of growth
promoting substances, hence there is no need for

22. (d) pH:
 The pH of the medium should be adjusted to
4.8 to 5.8 by adding sulphuric acid or lactic
acid.
 As the medium becomes highly anaerobic at
this range of pH, this inhibits the growth of
contaminating bacteria.
 There is no need of sterilizing the medium.
 Further anaerobic fermentation of alcohol
discourages growth of many microorganisms.
 However, pasteurization of the medium can
be done.

23. (iii) Fermentation:
Ethyl alcohol can be produced by any one of
the following processes:
1. Batch fermentation,
2. Continuous fermentation with cell, and
3. Continuous fermentation with cell recycling.
 A comparison of the operating parameters of the
above fermentation processes are indicated in table
3.5.
 However, batch fermentation is more commonly
employed for ethanol production.
 Production is carried out in a large fermenter with a
volume of 600 cm3.
 About 30% of inoculum (cell density 3 × 106 ml-1) is

24.  This addition of inoculum to the fermenter is called
as pitching.
 The following environmental factors like incubation
time and temperature are to be suitably maintained
and controlled in order to achieve optimum yield.
 The time required for the maximum yield of ethanol
is 30 to 72 hours, which largely depends upon the
specific gravity of the fermentation liquid.
 The fermentation is generally stopped at any hour
when the specific gravity of the fermentation liquid
becomes constant.
 At this stage, 6 to 8% of ethyl alcohol will be
formed.
 Fermentation generally starts within few hours of
yeasts inoculation.

25.  A temperature range of 25-30°C is favourable for
ethanol production.
 However, as heat is evolved during the
fermentation process, the temperature in the
fermenter gradually increases and is controlled
and maintained at the above indicated range by
means of cooling coils or by spraying cold water
around the fermenter.
 Periodical agitation of the fermenter is also
required for enforcing uniform cooling of the
medium.
 If higher temperatures are not controlled,
contamination of the fermentation broth may occur
due to the growth of thermophilic bacteria and also
result in the loss of ethanol due to surface
evaporation.
 When all the fermentation factors are optimum
there may be production of 1.9 grams of ethanol
one liter of medium per hour.

26. (iv) Harvest and Recovery:
 The cell mass is separated before distillation by
either centrifugation or sedimentation.
 It is then distilled in analyzer and rectifier columns to
get ethyl alcohol also called rectified spirit and fuel
alcohol (higher alcohols).
 A mixture containing 95.6% ethyl alcohol and 4.4%
water is obtained by fractional distillation.
 After distillation, the spent wash and bottom sludge
are drained out as distillery waste.
 The product is marketed as rectified spirit,
denatured spirit or special spirit.
 Zymomonas mobilis produces upto 120 g ethanol
per liter per hour.
 The flow diagram for the production of ethanol is
shown in the Fig. 3.6.

29.  Large distilleries employ, generally, special
rectifier column called as coffey’s still which
consists of two columns called as the analyzer
and the rectifier.
(a) The Analyzer:
 The analyzer is a vertical tower.
 It consists of columns arranged in a zigzag
manner.
 The fermentation liquid is allowed to flow down
the analyzer and simultaneously steam is allowed
to move up the tower from its bottom.
 Alcohol present in the fermentation liquid
vaporizes and its vapours collect at the bottom of

30. (b) The Rectifier:
 Just like analyzer, the rectifier is also a vertical
tower.
 It consists of specially designed fractionating
columns with a number of chambers.
 The less volatile constituents (the slop and fuel
oil) gradually condense and are drawn off from a
higher point of the still.
 The temperature at the higher point of still is
roughly equal to the boiling point.
 The head products, which are very less, contain
aldehydes, formic esters etc. owing to their
greater velocity, pass out through the top of the
column along with a small quantity of
uncondensed alcohol.

31. Applications of Ethyl Alcohol:
1. It is extensively used in synthesis of
variety of organic compounds and is a
universal solvent.
2. As energy source in motor fuel cells.
3. Different byproducts are useful in a
variety of ways.

32. Thank You