Topic wise notes

Alcohol

1. In chemistry, an alcohol is an organic compound in which the hydroxyl functional group (-O H ) 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 

Monohydric alcohols

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

Polyhydric alcohols

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

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

Alicyclic alcohols

C6H6(OH)6 Cyclohexane-1,2,3,4,5,6-hexol Inositol

C10H19OH 2 - (2-propyl)-5-methyl-cyclohexane-1-ol Menthol

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 (-O H ) 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 ProductionThere 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, Leuconostoc mesenteroides, Sarcina ventriculi, Zymomonas mobilis, etc.

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-5-phosphate, which is then cleaved by phosphoketolase into acetyl phosphate and glyceraldehyde-3-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. Fructose- l: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 ofATP from 2 molecules of ADP under anaerobic condition in contrast of 38 molecules of ATPThrough 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-d-glucosidase [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) andrelated 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 credentialsand 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 inthe 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 withoutproducing usable substrate. Some, like stone and tramp metal, are dangerous and may cause firesand explosions in the grain handling system. The more difficult contaminants to detect such asresidual insecticides and fumigants as well as mycotoxins, can be present at levels that canresult 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 lowinfestations may be more difficult to find. Also, the true grain weevils, because they bore intokernels, may not be visible on the surface of the grain. Only a few plants use a black light todetect 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 offersa 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 thegrain for moisture and slime presence.

A recent discussion with a group of farmers supplying corn to some of the newestfuel ethanol plants coming on stream was very revealing concerning the state of the corn marketin some areas of the country. The farmers were quite happy that the new distillers were payingthe same price for No. 2, 3, 4 and 5 grain as they are for No. 1. This seems not only wastefulon 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 dropthe contents of the railcar or truck into a pit from which the material is conveyed in some mannerto the storage bin. It is important that this station be constructed in a manner that allows it to bekept 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 andonward to the bin. This is unacceptable. The grid system should be designed for the rapid flow ofthe 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 alsoProvide more harborages for insects and are harder to clean and fumigate. Pneumatic systemstend to be abraded by the impingement of the grain on the tubing system, but a well-designedand 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 thatcannot 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 CAPACITYHow 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 arecontained 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 licensedindividuals, however it is necessary for the person in the company in charge of the sanitationprogram to have training and knowledge of pest control operations in order to evaluate the workof 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 millto 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. MillingThe 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 MILLSSome 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. CookingThe 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 bemoved 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 SYSTEMSIn 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 thefirst 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 SYSTEMSFew 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 SYSTEMThe 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 temperature-tolerant 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 SUGARSStep 1: gelatinizationThe purpose of cooking and saccharification is to achieve hydrolysis of starch into fermentablesugars, 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.