Topic wise notes
Alcohol
1. In chemistry, an alcohol is an organic compound in which the hydroxyl functional group
(-OH) is bound to a carbon atom. In particular, this carbon center should be saturated,
having single bonds to three other atoms.
2. An important class of alcohols is the simple acyclic alcohols, the general formula for
which is CnH2n+1OH. Of those, ethanol (C2H5OH) is the type of alcohol found in
alcoholic beverages, and in common speech the word alcohol refers specifically to
ethanol.
3. The most commonly used alcohol is ethanol, C2H5OH, with the ethane backbone. Ethanol
has been produced and consumed by humans for millennia, in the form of fermented and
distilled alcoholic beverages. It is a clear flammable liquid that boils at 78.4 °C, which is
used as an industrial solvent, car fuel, and raw material in the chemical industry.
4. The simplest alcohol is methanol, CH3OH, which was formerly obtained by the
distillation of wood and, therefore, is called "wood alcohol". It is a clear liquid
resembling ethanol in smell and properties, with a slightly lower boiling point (64.7 °C),
and is used mainly as a solvent, fuel, and raw material. Unlike ethanol, methanol is
extremely toxic: As little as 10 ml can cause permanent blindness by destruction of the
optic nerve and 30 ml (one fluid ounce) is potentially fatal.
5. Two other alcohols whose uses are relatively widespread (though not so much as those of
methanol and ethanol) are propanol and butanol. Like ethanol, they can be produced by
fermentation processes. (However, the fermenting agent is a bacterium, Clostridium
acetobutylicum, that feeds on cellulose, not sugars like the Saccharomyces yeast that
produces ethanol.) Saccharomyces yeast are known to produce these higher alcohols at
temperatures above 75 °F (24 °C). These alcohols are called fusel alcohols or fusel oils in
brewing and tend to have a spicy or peppery flavor. They are considered a fault in most
styles of beer.
6. Simple alcohols, in particular, ethanol and methanol, possess denaturing and inert
rendering properties, leading to their use as anti-microbial agents in medicine, pharmacy,
and industry.
Common names
Chemical Formula
IUPAC Name
Common Name
CH3OH
Methanol
Wood alcohol
C2H5OH
Ethanol
Grain alcohol
C3H7OH
Isopropyl alcohol
Rubbing alcohol
C4H9OH
Butyl alcohol
Butanol
C5H11OH
Pentanol
Amyl alcohol
C16H33OH
Hexadecan-1-ol
Cetyl alcohol
C2H4(OH)2
Ethane-1,2-diol
Ethylene glycol
C3H5(OH)3
Propane-1,2,3-triol
Glycerin
C4H6(OH)4
Butane-1,2,3,4-tetraol
Erythritol
C5H7(OH)5
Pentane-1,2,3,4,5-pentol
Xylitol
C6H8(OH)6
Hexane-1,2,3,4,5,6-hexol
Mannitol, Sorbitol
C7H9(OH)7
Heptane-1,2,3,4,5,6,7-heptol
Volemitol
Monohydric alcohols
Polyhydric alcohols
Unsaturated aliphatic alcohols
C3H5OH
Prop-2-ene-1-ol
Allyl alcohol
C10H17OH
3,7-Dimethylocta-2,6-dien-1-ol
Geraniol
C3H3OH
Prop-2-in-1-ol
Propargyl alcohol
C6H6(OH)6
Cyclohexane-1,2,3,4,5,6-hexol
Inositol
C10H19OH
2 - (2-propyl)-5-methyl-cyclohexane-1-ol
Menthol
Alicyclic alcohols
1. Applications
Alcohol has a long history of several uses worldwide. It is found in beverages for adults, as fuel,
and also has many scientific, medical, and industrial uses. The term alcohol-free is often used to
describe a product that does not contain alcohol. Some consumers of some commercially
prepared products may view alcohol as an undesirable ingredient, particularly in products
intended for children.
1. Alcoholic beverages
Alcoholic beverages, typically containing 5% to 40% ethanol by volume, have been produced
and consumed by humans since pre-historic times.
2. Antifreeze
A 50% v/v (by volume) solution of ethylene glycol in water is commonly used as an antifreeze.
3. Antiseptics
Ethanol can be used as an antiseptic to disinfect the skin before injections are given, often along
with iodine. Ethanol-based soaps are becoming common in restaurants and are convenient
because they do not require drying due to the volatility of the compound. Alcohol based gels
have become common as hand sanitizers.
4. Fuels
Some alcohols, mainly ethanol and methanol, can be used as an alcohol fuel. Fuel performance
can be increased in forced induction internal combustion engines by injecting alcohol into the air
intake after the turbocharger or supercharger has pressurized the air. This cools the pressurized
air, providing a denser air charge, which allows for more fuel, and therefore more power.
5. Preservative
Alcohol is often used as a preservative for specimens in the fields of science and medicine.
6. Solvents
Alcohols have applications in industry and science as reagents or solvents. Because of its
relatively low toxicity compared with other alcohols and ability to dissolve non-polar substances,
ethanol can be used as a solvent in medical drugs, perfumes, and vegetable essences such as
vanilla. In organic synthesis, alcohols serve as versatile intermediates.
Production
In industry, alcohols are produced in several ways:


By fermentation using glucose produced from sugar from the hydrolysis of starch, in the
presence of yeast and temperature of less than 37 °C to produce ethanol. For instance,
such a process might proceed by the conversion of sucrose by the enzyme invertase into
glucose and fructose, then the conversion of glucose by the enzyme zymase into ethanol
(and carbon dioxide).
By direct hydration using ethylene (ethylene hydration)[8] or other alkenes from cracking
of fractions of distilled crude oil.
What is Alcohol?
In chemistry, an alcohol is an organic compound in which the hydroxyl functional group (-OH)
is bound to a carbon atom. In particular, this carbon center should be saturated, having single
bonds to three other atoms. An important class of alcohols is the simple acyclic alcohols, the
general formula for which is CnH2n+1OH. The most commonly used alcohol is ethanol (C2H5OH)
is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol
refers specifically to ethanol. Ethanol has been produced and consumed by humans for millennia,
in the form of fermented and distilled alcoholic beverages. The simplest alcohol is methanol,
CH3OH, which was formerly obtained by the distillation of wood and, therefore, is called "wood
alcohol". It is a clear liquid resembling ethanol in smell and properties, with a slightly lower
boiling point (64.7 °C), and is used mainly as a solvent, fuel, and raw material. Two other
alcohols whose uses are relatively widespread (though not so much as those of methanol and
ethanol) are propanol and butanol. Like ethanol, they can be produced by fermentation processes.
(However, the fermenting agent is a bacterium, Clostridium acetobutylicum, that feeds on
cellulose, not sugars like the Saccharomyces yeast that produces ethanol.) Saccharomyces yeast
are known to produce these higher alcohols at temperatures above 75 °F (24 °C). These alcohols
are called fusel alcohols or fusel oils in brewing and tend to have a spicy or peppery flavor. They
are considered a fault in most styles of beer.
Microorganisms Used in Alcohol Production
There is a limited number of microorganisms which ferment carbohydrates (pentose or hexose
sugars) into alcohols and yield some by-products. Microorganisms utilize various pathways. A
summary of alcohol production through different routes of microorganisms is given. Following
are some of alcohol producing micro-organisms:
1. Bacteria: Clostridium acetobutylicum, Klebsiella pneumoniae,
mesenteroides, Sarcina ventriculi, Zymomonas mobilis, etc.
Leuconostoc
2. Fungi: Aspergillus oryzae, Endomyces lactis, Kloeckera sp., Kluyreromyees fragilis,
Mucor sp., Neurospora crassa, Rhizopus sp., Saccharomyces beticus, S. cerevisiae, S.
elltpsoideus, S. oviformis, S. saki,Torula sp., Trichosporium cutaneum, etc.
Production of alcohols by microorganism 1-Lactobacillus brevis; 2-Leuconostoc mesenteroides.
Ethanol Formation by Bacteria
1. Sarcina ventriculi
Sarcina ventriculi form ethanol through fructose-1:6-bisphosphate pathway i.e. EMP pathway
and pyruvate decarboxylase as formed by yeasts.
2. Zymomonas mobilis
A rod shaped polarly flagellated and motile bacterium (Zymomonas mobilis) is known to
metabolize glucose through the Entner-Doudoroff pathway and results in pyruvic acid. Pyruvic
acid is then decarboxylysed by pyruvate decarboxylase to acetaldehyde and carbon dioxide.
Acetaldehyde is reduced to ethanol. Thus, the fermentation products are ethanol, carbon dioxide
(and small amount of lactic acid). In some members of Enterobacteriaceae and Clostridia,
ethanol is formed as a subsidiary product. Acetaldehyde is not directly produced from pyruvic
acid by pyruvate decarboxylase, but originates through reduction of acetyl CoA.
3. Leuconostoc mesenteroides
Lactobacilli (e.g. Leuconostoc mesenteroides) use quite different pathway for alcohol
production. In the beginning of fermentation they utilize pentose cycle to result in xylulose-5phosphate, which is then cleaved by phosphoketolase into acetyl phosphate and glyceraldehyde3-phosphate. Acetaldehyde dehydrogenase and alcohol dehydrogenase reduce the
acetylphosphate into ethanol. Similarly, glyceraldehyde-3-phosphate is converted via pyruvic
acid to lactic acid (Schlegel, 1986).
4. Clostridium acetobutylicum
Clostridium acetobutylicum, ATCC 824, is a commercially valuable bacterium sometimes called
the "Weizmann Organism", after Jewish-Russian born Chain Weizmann, then senior lecturer at
the University of Manchester, England, used them in 1916 as a bio-chemical tool to produce at
the same time, jointly, acetone, ethanol, and butanol from starch. The method was described
since as the ABE process, (Acetone Butanol Ethanol fermentation process), yielding 3 parts of
acetone, 6 of butanol and 1 of ethanol, reducing the former difficulties to make cordite, an
explosive, from acetone and paving the way also, for instance, to obtain vehicle fuels and
synthetic rubber
5. Ethanol Formation by Yeasts
Yeasts, especially strain of S. cerevisiae are the main producer of ethanol. They have been used
as a major biological tool for the formation of ethanol since the discovery of fermentation
process by the time of L. Pasteur. During 1890s fermentation of froth was discovered in sugar
solution on addition of yeast extracts obtained by its grinding. This was the first evidence for a
biochemcial process of in vitro formation of ethanol in the absence of yeast cells. The extract
supplied inorganic phosphate (Pi) which is incorporated in fructose-l:6-bisphosphate. Fructosel:6-bisphosphate is accumulated due to lack of ATP utilization for energy requiring reactions in
the cell free systems. Therefore, an excess of ATP is maintained. The reaction is given below:
2C6H12O6+pi=>> 2C2H5OH +2CO2+2H2O+fructose-1:6-bisphosphate
This equation is known as Harden - Young equation after the name of the discoverer. Energetic
of EMP pathway reveals that one molecule of glucose yields only 2 molecules of
ATP from 2 molecules of ADP under anaerobic condition in contrast of 38 molecules of ATP
Through respiration:
C6Hl2O6 + 2Pi + 2ADP =>>2C2H5OH+2Co2+2H2O+2ATP + energy.
.
Outline of alcohol production by yeast cells
6. Neurospora crassa
Two strains of Neurospora crassa have been identified which utilize cellulase and produce
extracellular cellulase [see 1, 4-(1,3; 1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4] and β-dglucosidase [β-d-glucoside glucohydrolase, EC 3.2.1.21]. The activities were detected as early as
48 h in the culture broth. These cultures also fermented d-glucose, d-xylose and cellulosic
materials to ethanol as the major product of fermentation. The conversion of cellulose to ethanol
was >60%, indicating the potential of using Neurospora for the direct conversion of cellulose to
ethanol.
7. SACCHAROMYCES CEREVISIAE
Saccharomyces cerevisiae is in the fungi kingdom. The reasons for this classification are because
it has a cell wall made of chitin, it has no peptiodglycan in its cell walls, and its lipids are ester
linked. It also uses DNA template for protein synthesis and it has larger ribosomes. It is then
consider yeast because it is a unicellular organism so it can not form a fruiting body; like other
fungi.
Importance: Saccharomyces cerevisiae is one of the most important fungi in the history of the
world. This yeast is responsible for the production of ethanol in alcoholic drinks and is the
reasons your mother’s bread dough rises in the pan. That is where the names brewer’s and
baker’s yeast come from. The process in which it produces ethanol is one way this yeast converts
glucose into energy. There are two ways Saccharomyces cerevisiae breaks down glucose. One
way is through aerobic respiration. This process requires the presence of oxygen. When oxygen
is not present the yeast will then go through anaerobic fermentation. The net result of this is two
ATP, and it also produces two by products; carbon dioxide and ethanol. So if this yeast is
allowed to grow in a container lacking oxygen it will produce ethanol (alcohol). Humans have
been isolating this process since the beginning of history. The yeast helps in the rising of bread
with its other by-product carbon dioxide. The gas that is produce inside the dough causes it to
rise and expand. Both of these processes use the haploid of this yeast for this process. In industry
they isolate one strain, either a or ά, of the haploid to keep them from undergoing mating.
(Madigan, 457) In the baker’s yeast they have a strain were the production of carbon dioxide is
more prevalent then ethanol and vice versa for brewing. (Tomvolkfungi.net) Another
importance is that “live yeast supplementation to early lactating dairy goats significantly
increased milk production”.
“Grain handling: a critical aspect of distillery operation”
1. Introduction
Until recently, sanitation in grain handling has been basically ignored by the distilling industry,
except for those engaged in beverage alcohol production. We are forced to realize that a good
sanitation program and procedures are essential to the bottom line. Outbreaks of food animal
diseases such as BSE (Bovine spongiform encephalopathy) and food-borne diseases such
salmonella, as well as prohibitions against mycotoxins and insecticides in grains going into food
animals and ultimately the human food chain, have grabbed our attention. We suddenly realize
that distillers dried grains with solubles (DDGS) is a valuable co-product and not just an
unavoidable nuisance. Also, if we cannot sell it because of contamination, we are out of
business.
We first became aware of the importance of a sanitation program in grain handling
systems some years ago in the brewing industry. Breweries by definition prepare a food product,
beer, and are subject to all possible scrutiny by the Food and Drug Administration (FDA) and
related state and local food safety bureaus. Breweries routinely underwent very involved
inspections for food contamination and looked forward to them with much dread. In the 1970s,
a group of federal inspectors appeared at one plant and after providing the proper credentials
and the warrants necessary for the inspection, surprised the staff by asking only for a sample of
brewer’s spent grains. The staff relaxed and gladly obtained a sample of spent grains under the
inspectors’ directions. Two weeks later the plant was upset with a notice of citation for improper
sanitation procedures since insect fragments, mold, mycotoxins and insecticide residuals were
found in those spent grains. Since animal feed laws were less stringent in the 1970s than today,
the plant was allowed to continue selling the spent grains. The agency just used the
contamination detected as a means of bringing attention to an inadequate sanitation program as
established for breweries under the Federal Food, Drug and Cosmetic Act.
1. FORMS OF CONTAMINANTS, DETECTION AND REMOVAL
First, it is important to be aware of the different forms of contamination that may be present in
the raw materials brought in for processing. Second, everything possible must be done to ensure
detection of such contamination before it enters the facility. And, third, everything possible must
be done to avoid, remove or destroy the contaminants before using these raw materials. These
three are very closely related.
What kind of contaminants can we expect? Among others, insects, rodents and birds
and their droppings, stone, cobs, weed seeds, glass, wood, rags, tramp metal, residual
insecticides and fumigants, water, bacteria, mold and mycotoxins. Some of these are from
unclean grain handling and transport. Others have been added as fillers, adding weight without
producing usable substrate. Some, like stone and tramp metal, are dangerous and may cause fires
and explosions in the grain handling system. The more difficult contaminants to detect such as
residual insecticides and fumigants as well as mycotoxins, can be present at levels that can
result in unmarketable DDGS.
Bushel weight, moisture, damaged kernel and broken kernel/foreign material tests
are run immediately. High insect infestation may be determined by visual inspection, but low
infestations may be more difficult to find. Also, the true grain weevils, because they bore into
kernels, may not be visible on the surface of the grain. Only a few plants use a black light to
detect aflatoxin presence. Black light is also usable for the detection of rodent urine
contamination. This should be a routine test for all shipments in all plants. NIR technology offers
a solution to many of the grain testing needs for quick decision making by distillers.
Do not neglect the senses. Examine the grain, checking for insect presence, rodent
droppings, bird feathers as well as foreign seeds and extraneous matter such as cobs, straw, wood
and metal. Smell the material for any hint of mold presence or chemical contamination. Feel the
grain for moisture and slime presence.
A recent discussion with a group of farmers supplying corn to some of the newest
fuel ethanol plants coming on stream was very revealing concerning the state of the corn market
in some areas of the country. The farmers were quite happy that the new distillers were paying
the same price for No. 2, 3, 4 and 5 grain as they are for No. 1. This seems not only wasteful
on the part of the distiller, but potentially dangerous. The more allowable extraneous content in
the lower grade incoming grain, the greater the contribution to lower yields and the higher
likelihood of gross contamination and possible ignition of fires and explosions.
High moisture is the most common reason for rejection of a shipment. This is a
good start. High moisture contributes to difficulties in milling and handling and to lower yields.
High moisture also contributes to elevated mold growth, which typically leads to contamination
with mycotoxins that become concentrated in the DDGS.
First, decide on specifications for acceptance of the incoming substrate. Next,
provide the people and the testing equipment to determine if the substrate meets those
specifications. Stick to the established specifications. Only when satisfied should you begin to
unload the material into the plant’s infrastructure.
2. RECEIPT AND STORAGE
Specifications should call for all shipments to be received in covered hopper
railroad cars and hopper trucks fully covered by tarpaulin or some other means. This will help
prevent appearance of rodents and other pests while the shipment is in transit.
Once the shipment is accepted, it can then proceed to the unloading area. Most people drop
the contents of the railcar or truck into a pit from which the material is conveyed in some manner
to the storage bin. It is important that this station be constructed in a manner that allows it to be
kept in good sanitary condition without much effort. Pay attention to the grid covering the pit.
Some grids have wide-spaced bars that could allow whole rats to pass through to the pit and
onward to the bin. This is unacceptable. The grid system should be designed for the rapid flow of
the grain and nothing else. There are many different styles of grain conveying systems, including
bucket elevators, positive and negative pneumatic systems, belt conveyors and the newer
pulse pneumatic systems. The most user unfriendly and dangerous system seems to be the
bucket elevator. This is due to the high number of parts with a greater maintenance requirement
and the higher number of possible ignition points.
Manufacturers have attempted to alleviate some of this by the introduction of plastic buckets,
but the hangers and chains are still, for the most part, made of metal. Bucket elevators also
Provide more harborages for insects and are harder to clean and fumigate. Pneumatic systems
tend to be abraded by the impingement of the grain on the tubing system, but a well-designed
and balanced system can extend the life expectancy of the tubes indefinitely.
Grain should ideally be cleaned on the way to the bin. Grain should ideally be cleaned on the
way to the bin. Why store dust, straw, cobs, wood, metal, dead rats and other extraneous
material? Unfortunately, most of the systems we see are similar to Figure 1.
The facility illustrated in Figure 1 is typical in breweries since the brewers are not really
receiving raw materials, but barley that has been cleaned and processed by malting. For brewers
such a system works well. The earlier fuel ethanol plants had systems like this installed because
the engineers had been designing for breweries for a number of years and did not recognize that
distillers are involved in handling a different type of material. Distillers have become aware of
this and are requesting that cleaning systems be placed ahead of the bins. Keep records of the
amount of debris removed, as you do not want to pay for trash. Keeps a record of the net amount
of clean substrate entering the storage bin? This figure will be helpful later in determining true
yield. Bins should be constructed of concrete or metal and be well sealed. We have seen bins
constructed of corrugated metal sheets that leaked so badly that the grain was beginning to
ferment in the storage bin after a very light rainfall. One of the most important design criteria for
grain bins is their ability to be fully emptied.
We have seen too many storage bins at distilleries that hold 3-5 days of material that
cannot be totally emptied. This can be very dangerous and conducive to infestation. Mold
growing in stationary grain simply contaminates successive loads. One of the great tools for
protection against insect infestation is the understanding of the life cycles of the various insect
pests. Interrupting that life cycle prevents an infestation from becoming established. A 3-5 day
storage limit of grain in a bin will interrupt the life cycle of the common grain insects, but the bin
must be totally emptied each time it is filled. If the design does not allow total emptying, there
will be a continuous infestation.
3. STORAGE CAPACITY
How large should storage capacity be? Financial and logistic experts must contribute to this
decision. Storage capacity must accommodate both the processing schedule and cash flow
consideration. If running 24-hrs a day, seven days a week and 50 weeks of the year, then either
storage capacity or local sources of substrate must keep the plant supplied. Local supplies reduce
storage needs, so that capacity may be needed only to maintain supplies through weekends and
holidays. If shipments must come from a far, more capacity is needed. This is where the logistics
advice is needed.
4. The sanitation program
Sanitation programs must be adjusted to the type of facility. Very few large operations today are
contained within a structure. Most are of an open air design. The enclosed plant has the
sanitation advantage of controlled entry and egress, making it easier to exclude rodents and birds.
Regardless of design, full inspection and cleaning techniques must not be relaxed. Spills must be
cleaned up quickly to prevent attracting pests. Scrape, shovel and vacuum the debris. Never use
an air hose since the subsequent dispersal just spreads infestation and infection. Any inspection
and cleaning program should be familiar with storage insect life cycles and take advantage of
this knowledge. Full inspections of the total operation should be made every two weeks and
inspections of the more critical zones should take place on a weekly basis. Any evidence of an
unwanted invasion should be dealt with immediately. The cleaning schedule should also be
devised with the insect life cycle in mind. Certain areas of the plant, like the receiving station
and subsequent conveyors, dust collectors and air conveyor systems require more frequent
inspection, cleaning and possibly fumigation on a very regular basis. The program should
determine the risk and set the appropriate schedule.
A pest control program can be dangerous in the hands of unqualified people. Bait
stations, insecticides, and fumigants are poisons and harmful to humans, animals and pets as well
as the pests they are intended to control. These compounds are handled and applied by licensed
individuals, however it is necessary for the person in the company in charge of the sanitation
program to have training and knowledge of pest control operations in order to evaluate the work
of the hired contractors.
With the direction and agreement of management, establish the program. Determine the
inspection schedule. Hire the pest control firm. Determine the schedule for application of the
tools and chemicals of the pest control operation. Determine the cleaning schedule. Keep
complete records. Record keeping cannot be stressed too strongly. Obtain all reports from the
contract pest control operation including the dates of application, the places of application, the
chemicals used in the application, the strength of the materials used, the technician performing
the service and the records and results of their inspections as well as the results of the service.
Review the work of the hired contractor for effectiveness. Review the program and make
appropriate changes as they are necessary
“Grain dry milling and cooking procedures: extracting sugars in preparation
for fermentation”
In brief, in this dry milling process the whole cereal, normally corn (maize), is ground in a mill
to a fine particle size and mixed with liquid, usually a mixture of water and backset stillage. This
slurry is then treated with a liquefying enzyme to hydrolyze the cereal to dextrins, which are a
mix of oligosaccharides. The hydrolysis of starch with the liquefying enzyme, called α-amylase,
is done above the temperature of gelatinization of the cereal by cooking the mash at an
appropriate temperature to break down the granular structure of the starch and cause it to
gelatinize. Finally the dextrins produced in the cooking process are further hydrolyzed to glucose
in a saccharification process using the exoenzyme glucoamylase, and possibly another enzyme
(Rhizozyme™). These enzymes may also be added to the yeast propagation tank or the
fermentor. These separate stages of milling, cooking and saccharification will be explained in
more detail. This is called the dry milling process.
1. Milling
The purpose of milling is to break up the cereal grains to appropriate particle size in order
to facilitate subsequent penetration of water in the cooking process. The optimum size of the
ground particle is the subject of disagreement. Some engineers believe the particle should be as
fine as possible to allow the water maximum access for hydrolysis of starch while others believe
a better yield is obtained if the particles are larger and the jet cooker can act on the particles. The
key is simply to expose the starch without grinding so fine as to cause problems in co-product
recovery. A wide variety of milling equipment is available to grind the whole cereal to a meal.
Normally, most distilleries use hammer mills, although some may use roller mills, particularly
for small cereal grains.
1.1.HAMMER MILLS
In a hammer mill, the cereal grain is fed into a grinding chamber in which a number of hammers
rotate at high speed. The mill outlet contains a retention screen that holds back larger particles
until they are broken down further so that there will be a known maximum particle size in the
meal. The screens are normally in the size range of 1/8-3/16 in. (2-4 mm). Sieve analysis
(particle size distribution) shows whether the hammer mill screens are in good order and whether
the mill is correctly adjusted, and should be conducted regularly. Table 1 shows a typical sieve
analysis for corn. The two largest screens retain only 11% of the particles while the quantity
passing through the 60-mesh screen is also fairly low at 7%. For efficient processing of the
cereal starch into alcohol, the particles should be as fine as possible. However a compromise
must be made such that the particles are not so fine that they cause balling in the slurry tank or
problems in the by-product recovery process. Sometimes the sieve analysis will vary depending
on the severity of the shaker and a consistent shaking should be done each time the test is done.
Fineness of the grind can be significant factor in the final alcohol yield. It is possible to obtain a
5-10% difference in yield between a fine and a coarse meal. Table 2 shows the typical alcohol
yield from various cereals. It can be seen that the normal yield from corn is 2.85 gallons of
anhydrous ethanol per bushel (56 lbs). However, the yield with coarsely ground corn may drop
to 2.65 gallons per bushel, a reduction in yield of 7.5%. This is a highly significant reduction and
would have serious economic consequences for any distiller. Grinding is about expanding the
amount of surface area. When more surface area is exposed, water and enzymes are better able to
penetrate the kernel. A particle 1 in. in diameter has a total surface area of 6 in2. If you grind the
1 in. particle into 1,000 particles,surface area becomes 6,000 in2. No amount of heating or
‘exploding’ will overcome poor grind as measured by yield. The key is to expose more surface
area, but to do so in a controlled manner. Since grind is so important, it is recommended that a
sieve analysis of the meal be done at least once per shift. The distiller should set specifications
for the percentage of particles on each sieve; and when the measured quantity falls outside these
specifications the mill should be adjusted. Normally the hammers in a hammer mill are turned
every 15 days, depending on usage; and every 60 days a decision should be made as to whether
or not to replace the hammers and screens.
Since sieve analysis is critical, a case can also be made for recycling to the hammer mill any
grain not ground sufficiently fine. Fineness of the grind also has an important bearing on
centrifugation of the stillage post-distillation. A finer grind may yield more solubles and hence
place a greater load on the evaporator. However since the key is to maximize yield, dry house
considerations, while important, cannot override yield considerations.
1.2.ROLLER MILLS
Some distillers use roller mills
(e.g.
malt
whisky
producers),
particularly where cereals containing
substantial quantities of husk material
are used. In a roller mill, the cereal is
nipped as it passes through the rollers,
thus exerting a compressive force. In
certain cases, the rollers operate at
different speeds so that a shearing force
can be applied. The roller surfaces are
usually grooved to aid in shearing and
disintegration. Figure 1 shows the
general configuration of a roller mill.
In Scotland the solids in whisky mash, made entirely from malted barley, are usually removed by
using a brewery-type lauter tun, which is a vessel with a perforated bottom like a large colander.
In this case, a roller mill should be used as the shear force allows the husk to be separated with
minimal damage. The husk then acts as the filter bed in the lauter tun for the efficient separation
of solids and liquid.
2. Cooking
The purpose of cooking is 5-fold:
Sterilization.The mash must be sterilized so that harmful bacteria are minimized. A brewer
achieves this by boiling mash (wort) while the distiller achieves it by cooking.
Solubilization of sugars. Sugars are solubilized to a certain point, typically 2-3% free sugars. In
this way yeast growth can occur rapidly but not excessively as would happen if too much sugar
was released at once.
Release of all bound sugars and dextrins (chains of sugar). Extraction must occur such that
subsequent enzymatic hydrolysis can ensure that all sugars are utilized. Starch (precursor of
sugars) is in large bound to protein and fiber, which is are freed during cooking.
Protein breakdown to amino acids should be minimized. Amino acids and peptides can
become bound to sugars in Maillard reactions, which leaves sugar unavailable.
Reduction in viscosity. Following gelatinization, viscosity is reduced allowing the slurry to be
moved through lines for subsequent processing.
Cooking is the entire process beginning with mixing the grain meal with water (and
possibly backset stillage) through to delivery of a mash ready for fermentation.
Figure 2 shows the components that make up a typical milling and cooking system. This
schematic diagram could represent the processes involved in beverage, industrial or fuel alcohol
production, except that nowadays only the whisky distillers use malt as a source of liquefying
and saccharifying enzymes. All other alcohol producers use microbial enzyme preparations. The
fastest enzyme systems have low calcium requirements (2-5 ppm), lower pH optima (less
buffering required) and high temperature stability. They are designed to reduce viscosity, with
less emphasis on DE. The key to cooking is to liquefy the starch so it can be pumped to the
fermentor, hence viscosity is critical.
2.1 Cooking systems
a. BATCH COOKING SYSTEMS
In considering all the different processes that make up cooking, it should first be
explained that there are a variety of batch and continuous cooking systems. For a batch system
there is usually only one tank, which serves as slurrying, cooking and liquefaction vessel. Live
steam jets are typically installed in the vessel to bring the mash to boiling temperature along with
cooling coils to cool the mash for liquefaction.
Figure 3 Batch Cooking System
Figure 3 shows a typical batch cooking system. In the batch cooking system, a weighed quantity
of meal is mixed into the vessel with a known quantity of water and backset stillage. These
constituents of the mash are mixed in simultaneously to ensure thorough mixing. The quantity of
liquid mixed with the meal will determine the eventual alcohol content of the fermented mash.
when a distiller refers to a ’25 gallon beer’, it means 25 gallons of liquid per bushel of cereal. For
example, for a corn distillery with an alcohol yield of 2.5 gallons of absolute alcohol per bushel,
the 25 gallons of liquid would contain 2.5 gallons of alcohol. Therefore it would contain 10%
alcohol by volume (abv). Using the distillery alcohol yield, the distiller can determine the
quantity of cereals and liquid to use.
In the batch cooking system, a small quantity of α−amylase is added at the beginning (0.02%
w/w of cereal) to facilitate agitation in the high viscosity stage at gelatinization. After boiling,
usually for 30-60 minutes, (sometimes under a slight pressure), the mash is cooled to 75-90°C
and the second addition of α−amylase made (0.04-0.06% w/w cereal). Liquefaction then takes
place, usually over a holding period of 45-90 minutes. The mash should always be checked at
this stage to make certain that no starch remains. Starch produces a blue or purple color with
iodine. Mash should not be transferred from the liquefaction hold until it is ‘starch-negative’.
The pH range for efficient α−amylase usage is 6.0-6.5, although enzymes with good activity at
pH 5.5-5.7 are now available. Therefore, mash pH should be controlled in this range from the
first enzyme addition until the end of liquefaction. The glucoamylase enzyme has a lower pH
range (4.0-5.5), so after liquefaction the pH of the mash should be adjusted with either sulfuric
acid or backset stillage, or a combination of the two.
The quantity of backset stillage as a percentage of the total liquid varies from 10 to 50%. On one
hand, the backset stillage supplies nutrients essential for yeast growth. However too much
backset stillage can result in the oversupply of certain minerals and ions that suppress good
fermentation. Especially noteworthy are the sodium, lactate and acetate ions. Sodium
concentrations above 0.03% or lactate above 0.8% or acetate above 0.03% can inhibit yeast
growth and can slow or possibly stop the fermentation prematurely. Overuse of backset (or even
process condensate water) must be avoided to prevent serious fermentation problems.
b. CONTINUOUS COOKING SYSTEMS
Few distilleries outside of beverage plants use batch cooking. Most fuel ethanol distilleries use a
continuous cooking system. In the continuous cooking process (Figure 4) meal, water and
backset stillage are continuously fed into a premix tank. The mash is pumped continuously
through a jet cooker, where the temperature is instantly raised to 120°C. It then passes into the
top of a vertical column. With plug flow, the mash moves down the column in about 20 minutes
and passes into the flash chamber for liquefaction at 80-90°C. High temperature tolerant
α−amylase is added at 0.04-0.08% w/w cereal to bring about liquefaction. The retention time in
the liquefaction/flash chamber is a minimum of 30 minutes, but should be at least 60 minutes.
The pH from slurrying through to the liquefaction vessel must be controlled within the 6.0-6.5
range. The greatest advantage of this system is that no enzyme is needed in the slurrying stage,
leading to significant savings in enzyme usage. It is critical to have plug flow through the
chamber along with good enzyme dispersion. The mash should have a relatively low viscosity
and dextrose level of 2-3%. Modern systems have 29-33% solids. From the liquefaction
chamber, the mash is pumped through a heat exchanger to fermentation.
Figure 4 Continuous columnar cooking system.
c. CONTINUOUS U-TUBE COOKING SYSTEM
The continuous U-tube cooking system (Figure 5) differs from the columnar
cooking system in that the jet cooker heats the mash to 120-140°C prior to being transferred
through a continuous U-tube. The retention time in the U-tube is only three minutes, after which
it is flashed into the liquefaction vessel at 80-90°C and the enzyme is added (high temperaturetolerant α-amylase 0.05-0.08% w/w cereal). The residence time in the liquefaction vessel is a
minimum of 30 minutes. The main advantage of this system is the relatively short residence
period in the U-tube. If properly designed there is no need to add any α−amylase enzyme in the
slurrying stage. However, because of the relatively narrow diameter of the tubes, some distillers
add a small amount of enzyme to the slurry tank to guarantee a free flow.
Figure 5. High temperature, short time, continuous U-tube cooking system.
3. COMPARING COOKING SYSTEMS
The relative heat requirements of the three cooking systems can be seen in Table 3. Surprisingly,
the batch system is the most energy-efficient. Batch systems also generally use less enzyme than
the other systems, possibly due to the difficulty of accurate dosing and good mixing with the
continuous systems. The main disadvantage of the batch system compared to the continuous
system is the poor utilization or productivity per unit of time. The temperature-time sequences
for the three systems shown in Figure 6 demonstrate how much more efficiently time is used in
continuous systems compared to the batch system.
Table 3. Relative heat requirements of cooking systems.
Batch
1
Continuous columnar
1.18
Continuous U-tube
1.37
In the continuous systems, the flow diagrams show steam addition to raise the mash temperature.
This temperature increase is brought about instantaneously by a jet cooker or ‘hydroheater’.One
purpose of the cooking process is to cleave the hydrogen bonds that link the starch molecules,
thus breaking the granular structure and converting it to a colloidal suspension. Another factor in
the breakdown of starch is the mechanical energy put into the mash via agitation of the different
vessels in which the cooking process takes place. Well-designed agitation is very important in a
cooking system; and the problem is intensified when plug flow is also desired. Mash viscosities
give an indication of the relative ease or difficulty with which some cereals are liquefied. Figure
12 compares viscosity against temperature for corn and waxy maize (amioca) and illustrates the
difference in viscosity profiles.
All of the cooking systems described require the addition of enzymes at
least for the liquefaction stage where most of the hydrolysis takes place. Many distilleries now
use a high temperature-tolerant α−amylase. The optimum pH range for this enzyme is between
5.8 and 6.5, although it shows good stability up to pH 8.5 (Figure 13) while the optimum
temperature range is 88°C-93°C (Figure 14). Typically, this type of enzyme would be used at
between 0.04% and 0.08% by weight of cereal. Where it is necessary to add some α−amylase
enzyme to the slurrying vessel, the dosage rate may be slightly higher
Figure 6. Temperature/time sequences in various types of cooking systems
Figure 7. Increasing viscosity with cooking temperature.
Figure 8.Effect of pH on activity of α-amylase.
The reaction time for enzyme-catalyzed reactions is directly proportional to the concentration of
enzyme. Consequently, distillers wishing to minimize the quantity of enzyme used should
design equipment to have long residence times to allow the reactions to be completed with
minimal dosage of enzyme.
4. HYDROLYSIS OF STARCH TO FERMENTABLE SUGARS
Step 1: gelatinization
The purpose of cooking and saccharification is to achieve hydrolysis of starch into fermentable
sugars, which is accomplished by the endoenzyme α−amylase, followed by the exoenzyme
glucoamylase (amyloglucosidase) to release glucose. However in order for the α-amylase to gain
access to the starch molecules, the granular structure of the starch must first be broken down in
the process known as gelatinization. When the slurry of meal and water are cooked, the starch
granules start to adsorb water and swell. They gradually lose their crystalline structure until they
become large, gel-filled sacs that tend to fill all of the available space and break with agitation
and abrasion. The peak of gelatinization is also the point of maximum viscosity of a mash.
Figures 9, 10 and 11 show the progressive gelatinization of cornstarch, as viewed on a
microscopic hot stage. In Figure 9 the granules are quite distinct and separate from the
surrounding liquid. In Figure 10 these same granules have swollen in size and some of the liquid
has entered the granules.
Figure 9 Gelatinization of cornstarch. Starch granules viewed on microscope hot stage at
67°C (under normal illumination)
Figure 11 shows the granules as indistinct entities in which the liquid
has entered to expand them considerably. Gelatinization temperatures vary for the different
cereals (Table 4). Some distillers consider it important for the slurrying temperature of the meal
Table
4
Gelatinization
temperature
ranges
of
various
feedstocks.
to be below the temperature of gelatinization. This avoids coating of grain particles with an
impervious layer of gelatinized starch that prevents the enzymes from penetrating to the starch
granules and leads to incomplete conversion. Many distillers, however, go to the other extreme
and slurry at temperatures as high as 90°C (190°F). At these temperatures starch gelatinizes
almost immediately and with adequate agitation there is no increase in viscosity and no loss of
yield.
Figure 10. Gelatinization of cornstarch. Same granules as in Figure 9 at 75°C (under
normal illumination)
Figure 11. Gelatinization of cornstarch. Same granules as in Figures 9 and 10 at 85°C
(under normal illumination).
Step 2. Liquefaction: hydrolysis of starch to dextrins
Liquefaction is accomplished by the action of α−amylase enzyme on the exposed starch
molecules. Starch exists in two forms. One form is the straight-chained amylose, where the
glucose units are linked by α−1,4 glucosidic linkages. The amylose content of corn is about 10%
of the total starch; and the amylase chain length can be up to 1,000 glucose units.
The other form of starch is called amylopectin,which
represents about 90% of the starch in corn. Amylopectin has a branched structure. It has the same
α−1,4 glucosidic linkages as in amylose, but also has branches connected by α−1,6 linkages. The
number of glucose units in amylopectin can be as high as 10,000. Corn, wheat and sorghum
(milo), the three most common feedstocks for ethanol production, have similar levels of starch,
but percentages of amylose and amylopectin differ with grain and with variety. Starch structures
are reviewed in greater detail in the chapter by R. Power in this volume. The α−amylase enzyme
acts randomly on the α−1,4 glucosidic linkages in amylose and amylopectin but will not break
the α−1,6 linkages of amylopectin. The resulting shorter straight chains (oligosaccharides) are
called dextrins, while the shorter branched chains are called α-limit dextrins. The mixture of
dextrins is much less viscous.
Step 3. Saccharification: release of glucose from dextrins.
Saccharificationis the release of the individual glucose
molecules from the liquefied mixture of dextrins. The dextrins will be of varying chain lengths.
However, the shorter the chain length the less work remaining for the exoenzyme glucoamylase,
which releases single glucose molecules by hydrolyzing successive α−1,4 linkages beginning at
the non-reducing end of the dextrin chain. Glucoamylase also hydrolyzes α−1,6 branch linkages,
but at a much slower rate. One real problem with HPLC analysis is that dextrins are given as
total oligosaccharides with no differentiation between four glucose units and 20 glucose units.
The work of the glucoamylase is directly proportional to the length of the dextrin chain; and
there is currently no way of knowing how well the α-amylase has worked to produce small
oligosaccharides. In Scotch whisky production, malted barley is used as a source of both
α−amylase and the exoenzyme ß-amylase. The fermentable sugar produced is maltose, a dimer
made up of two glucose units.