Malting, Brewing and Distilling Introduction relevant to the country of origin and the descrip- The essential process involved in brewing is tion of the product. Consequently, added enzymes the conversion of cereal starch into alcohol to may contribute different proportions of the enzyme make a palatable, intoxicating beverage Fermen- complement The alcohol content of the liquor produced by tation is mediated by yeasts appropriate to the fermentation is limited by the tolerance of the cereal or cereals involved. Most yeasts used belong to the species Saccharomyces cerevisiae. yeasts. Probably the most tolerant yeasts are used which now includes the ' bottom yeast'previ in sake production. They can survive alcohol ously classified as S. carlsbergensis(Reed ar contents of about 20% although the Nagodawithana, 1991) sold in a diluted form Two processes are involved: the starch has first Distillation allows the concentration of alcohol enzymes, and second, the sugars have to be character of which depends on flavours imparted fermented to alcohol by enzymes present in yeast. added flavours usually being extracts from other In the first process the enzymes may be producc plant sources. exogenously, in other organisms present. Alter For alcohol production from plant material, natively they may be added as extracts sugars must be present, as in fleshy fruits, or other substrates from which fermentable sugars are employed is known as malting. This comprises can be produced. Starch is such a substrate,so a controlled germination during which enzymes capable of catalyzing hydrolysis, not only of the West, the most commonly used cereal is starch,but also other components of the grain, barley but substantial quantities are derived from are produced. The most significant are the pro- maize(beer in central America), rye(kvass beer teases and the B-glucanases, as the products in the former U.S.S. R), rice(sake in Japan and resulting from their activities affect the qualiti shaoshinchu in China), sorghum(beer in Africa). of the beverage Triticale may be used as an adjunct in beers Other organisms are employed as a source of zymes in the production of sake -a beer produced from rice. Enzymes are added in solu- Malting tion, particularly when it is required to hydrolyze During malting, large molecular weight com- he starch etc. present in endosperm grits or ponents of the endosperm cell fours, themselves incapable of enzyme produc- proteins and the starch granules, are hydrolyzed tion. Such adjuncts may provide any proportion by enzymes rendering them more soluble in of the total starch, depending on legislation water
9 Malting, Brewing and Distilling Introduction The essential process involved in brewing is the conversion of cereal starch into alcohol to make a palatable, intoxicating beverage. Fermentation is mediated by yeasts appropriate to the cereal or cereals involved. Most yeasts used belong to the species Saccharomyces cerevisiae, which now includes the ‘bottom yeast’ previously classified as S. carlsbergensis (Reed and Nagodawithana, 1991). Two processes are involved: the starch has first to be converted to soluble sugars by amylolytic enzymes, and second, the sugars have to be fermented to alcohol by enzymes present in yeast. In the first process the enzymes may be produced in the grains themselves (endogenously) or exogenously, in other organisms present. Alternatively they may be added as extracts. The process in which the grain’s own enzymes are employed is known as malting. This comprises a controlled germination during which enzymes capable of catalyzing hydrolysis, not only of starch, but also other components of the grain, are produced. The most significant are the proteases and the P-glucanases, as the products resulting from their activities affect the qualities of the beverage. Other organisms are employed as a source of enzymes in the production of sake - a beer produced from rice. Enzymes are added in solution, particularly when it is required to hydrolyze the starch etc. present in endosperm grits or flours, themselves incapable of enzyme production. Such adjuncts may provide any proportion of the total starch, depending on legislation water. relevant to the country of origin and the description of the product. Consequently, added enzymes may contribute different proportions of the enzyme complement. The alcohol content of the liquor produced by fermentation is limited by the tolerance of the yeasts. Probably the most tolerant yeasts are used in sake production. They can survive alcohol contents of about 20% although the product is sold in a diluted form. Distillation allows the concentration of alcohol into drinks described as spirits, the special character of which depends on flavours imparted by the processing or added to a distillate, the added flavours usually being extracts from other plant sources. For alcohol production from plant material, sugars must be present, as in fleshy fruits, or other substrates from which fermentable sugars can be produced. Starch is such a substrate, so all cereals can be used for beer production. In the West, the most commonly used cereal is barley but substantial quantities are derived from maize (beer in central America), rye (kvass beer in the former U.S.S.R), rice (sake in Japan and shaoshinchu in China), sorghum (beer in Africa). Triticale may be used as an adjunct in beers. Malting During malting, large molecular weight components of the endosperm cell walls, the storage proteins and the starch granules, are hydrolyzed by enzymes, rendering them more soluble in 21 8
MALTING, BREWING AND DISTILLING 219 All cereals are capable of undergoing maltingmalting barley is 1. 5%; some 38% of this but barley is particularly suitable because the appears in the beer in the form of soluble adherent pales (lemma and palea -see Ch. 2) nitrogen compounds, the proportion of the provide protection for the developing plumule, or total nitrogen entering the beer being some- acrospire, against damage during the necessary what larger from two-row than from six-row handling of the germinating grains. Further, the husk(pales)provides an aid to filtration when the malt liquor is being removed from the residue of of barley lies in the firmness of the grain at high Dormancy insoluble grain components. A third advantage Harvest-ripe barley may not be capable of Both two-row and six-row barleys(see Ch. 2) germination immediately. While this is advan- are suitable: the former are generally used tageous in the field, protecting the crop against Europe the latter in North America. Distinct sprouting in the ear, it is clearly a problem in varieties were formerly grown for malting. They tion occurring. the mechanism of dormancy is feeding. Modern malting varieties have high a single cause is involved in all cases; in many yields and are thus suitable for the less demanding instances it has been shown that germination is alternative uses also inhibited by inability of the embryo to gain access The characteristics required of a malting barley to oxygen. a distinct phenomenon known as water sensitivity' can arise during steeping if a 1. High germination capacity and energy, with film of water is allowed to remain on the surface adequate enzymic activity 2. Capacity of grains modified by malting to oxygen to satisfy the needs of the developing produce a maximum of extract when mashed embryo and it acts as a barrier to the passage of prior to fermentation air. Dormancy declines with time and storage is 3. Low content of husk thus not just a means of holding sufficient stocks 4. High starch and low protein contents of gral during the storage of freshly harvested it is an essential part of the process of and handling as well as by genetic factors: loss which dormancy has declined sufficiently for of germination capacity can result from damage malting proper to commence. Bothdormancy to the embryo during threshing, or overheating and 'water sensitivity'are defined in relation to during drying or storage. the test performed In one test 100 grains are Provided that grains are ripe, free from fungal germinated on filter papers with 4 and 8ml of infestation and intact, the yield of malt extract water, the difference between viability and the should be directly related to starch content germination on 4 ml of water is called dormancy 1. Starch content is lower sensitivity. Factors involved in controlling and 2. Longer malting times are required breaking dormancy have been reviewed by Briggs 3. Modification never proceeds as far as in low.(1978) nitrogen barley 4. The greater quantities of soluble proteins lead Barley malting operations to haze formation and may provide nutrients for b of the The average nitrogen content of schematically in Fig, 9/ n malting are shown eping The practical steps
MALTING, BREWING AND DISTILLING 219 malting barley is 1.5%; some 38% of this appears in the beer in the form of soluble nitrogen compounds, the proportion of the total nitrogen entering the beer being somewhat larger from two-row than from six-row types. All cereals are capable of undergoing malting but barley is particularly suitable because the adherent pales (lemma and palea - see Ch. 2) provide protection for the developing plumule, or acrospire, against damage during the necessary handling of the germinating grains. Further, the husk (pales) provides an aid to filtration when the malt liquor is being removed from the residue of insoluble grain components. A third advantage of barley lies in the firmness of the grain at high moisture content. Both two-row and six-row barleys (see Ch. 2) are suitable: the former are generally used in Europe, the latter in North America. Distinct varieties were formerly grown for malting. They were lower yielding than varieties grown for feeding. Modern malting varieties have high yields and are thus suitable for the less demanding alternative uses also. The characteristics required of a malting barley are: Dormancy Harvest-ripe barley may not be capable of germination immediately. While this is advantageous in the field, protecting the crop against sprouting in the ear, it is clearly a problem in relation to malting, which depends on germination occurring. The mechanism of dormancy is not fully understood and indeed it is unlikely that a single cauSe is involved in all cases; in many instances it has been shown that germination is inhibited by inability of the embryo to gain access to oxygen. A distinct phenomenon known as ‘water sensitivity’ can arise during steeping if a film of water is allowed to remain on the Surface of grains. The water contains too little dissolved oxygen to Satisfy the needs of the developing embryo and it acts as a barrier to the passage of air. Dormancy declines with time and storage is thus not just a means of holding sufficient stocks of grain, it is an essential part of the process of malting. During the storage of freshly harvested barley tests are performed to detect the time at which dormancy has declined sufficiently for malting proper to commence. Both ‘dormancy’ and ‘water sensitivity’ are defined in relation to the test performed. In one test 100 grains are germinated on filter papers with 4 and 8 ml of water, the difference between viability and the germination on 4 ml of water is called dormancy while the difference bemeen the levels of gedation on the different volumes of water is the watersensitivity. Factors involved in controlling and breaking dormancy have been reviewed by Briggs (1978). 1. High germination capacity and energy, with adequate enzymic activity. 2. Capacity of grains modified by malting to produce a maximum of extract when mashed prior to fermentation. 3. Low content of husk. 4. High starch and low protein contents. The above qualities Can be affected by husbandry and handling as well as by genetic factors: loss of germination capacity can result from damage to the embryo during threshing, Or overheating during drying or storage. Rovided that grains are ripe, free from fungal infestation and intact, the yield of malt extract should be directly related to starch content. High-nitrogen barley is unsuitable for malting because: 1. Starch content is lower. 2. Longer malting times are required. 3. Modification never proceeds as far as in lownitrogen barleys. 4. The greater quantities of soluble proteins lead to haze formation and may provide nutrients for bacteria and impair the keeping quality The practical steps in malting are shown of the beer. The average nitrogen content of Barley malting operations schematically in Fig. 9.1
220 TECHNOLOGY OF CEREALS At intervals the grain is mixed and turned to Clean, graded barley grain rovide more uniform growth opportunities, and to prevent the roots from matting together. As the embryo grows it produces hormones including Steeping gibberellic acid, stimulating production of hydro lytic enzymes in the scutellum and aleurone layer, leading to 'modificationof the starchy endo- Chit malt perm. The malting process is regulated by the initial choice of barley, the duration of growth the temperature, the grain moisture content Germination changes in the steeping schedule, and by use of additives. When modification is sufficient it is stopped by kilning the 'green malt,, that is, by drying and cooking it in a current of hot dry air The dry, brittle culms are then separated and the finished malt is stored. Dry malt is stable storage and, unlike barley, it is readily crushe Kilning The conditions of kilning are critical in deter mining the character of the malt: it can cause a slight enhancement of the levels found in green Finished malt malt or completely destroy it. Malt contains relatively large quantities of soluble sugars and nitrogenous substances and, if it has been kilned Milling at low temperatures, it contains high levels of hydrolytic enzymes. When crushed malt is mixed with warm water the enzymes catalyze hydroly Ground malt of the starch, other polysaccharides, proteins and nucleic acids accessible to them whether from FIG 9. 1 Diagrammatic summary of the malting process the malt or from materials mixed with it. Malt also confers colour, aroma and flavour to the Selected barley is'steeped', usually by immer- product. The solution of the products of hydrolysis sion in water, for a period chosen to achieve a extracted from the malt is the wort'. It forms particular moisture level. The water is drained the feedstock for fermentation for brewing or from the grain, which germinates. Conditions are distillation(Briggs, 1978 regulated to keep the grain cool (generally below One of the benefits derived from the applica 18C)and to minimize water losses. as the grain tion of technology in malting has been the reduc- germinates the coleoptile(acrospire) grows beneath tion in time required to produce satisfactory the husk and pericarp while the 'chit(coleorhiza, malts. The amount of time saved can be inferred root sheath)appears at the base of the grain, and from the diagrams in Fig. 9. 3. It is clear that is split by the emerging rootlets. Fig. 9.2 most saving has occurred during the present FIG 9. 2 Diagrammatic longitudinal sections through barley grains in the early I imbibed grain, 2. rootlets emerged, 3. Rootlets and coleoptile emerged om Briggs(1978), Barley (Fig. 1. 11). Reproduced by courtesy of Chapman and Hall Ltd
220 TECHNOLOGY OF CEREALS Malting Clean, graded barley grains At intervals the grain is mixed and turned to provide more uniform growth opportunities, and to prevent the roots from matting together. As the embryo grows it produces hormones including gibberellic acid, stimulating production of hydrolytic enzymes in the scutellum and aleurone layer, leading to ‘modification’ of the starchy endosperm. The malting process is regulated by the initial choice of barley, the duration of growth, the temperature, the grain moisture content, changes in the steeping schedule,and by use of additives. When modification is sufficient it is stopped by kilning the ‘green malt’, that is, by drying and cooking it in a current of hot dry air. The dry, brittle culms are then separated and the finished malt is stored. Dry malt is stable on storage and, unlike barley, it is readily crushed. Kilning Sprouts The conditions of kilning are critical in determining the character of the malt: it can cause a slight enhancement of the levels found in green Finished malt malt or completely destroy it. Malt contains relatively large quantities of soluble sugars and nitrogenous substances and, if it has been kilned at low temperatures, it contains high levels of hydrolytic enzymes. When crushed malt is mixed with warm water the enzymes catalyze hydrolysis of the starch, other polysaccharides, proteins and nucleic acids accessible to them, whether from the malt or from materials mixed with it. Malt also confers colour, aroma and flavour to the product. The solution of the products of hydrolysis extracted from the malt is the ‘wort’. It forms the feedstock for fermentation for brewing or distillation (Briggs, 1978). One of the benefits derived from the application of technology in malting has been the reduction in time required to produce satisfactory malts. The amount of time saved can be inferred from the diagrams in Fig. 9.3. It is clear that most saving has occurred during the present 1 Steeping 7 “Chit malt” Germination 1 Green malt +-Ma1t + Milling Ground molt FIG 9.1 Diagrammatic summary of the malting process. Selected barley is ‘steeped’, usually by immersion in water, for a period chosen to achieve a particular moisture level. The water is drained from the grain, which germinates. Conditions are regulated to keep the grain cool (generally below lS°C) and to minimize water losses. As the grain germinates the coleoptile (acrospire) grows beneath the husk and pericarp while the ‘chit’ (coleorhiza, root sheath) appears at the base of the grain, and is split by the emerging rootlets. Fig. 9.2. 0 1 2 3 FIG 9.2 Diagrammatic longitudinal sections through barley grains in the early stages of germination. 1. imbibed grain, 2. rootlets emerged, 3. Rootlets and coleoptile emerged. From Briggs (1978), Barley (Fig. 1.11). Reproduced by courtesy of Chapman and Hall Ltd
MALTING, BREWING AND DISTILLING 221 6-8d o-35d 4-6d B863-7d 3-6d 3-6d 3 d IG9.3 Diagram showing the reduction, over three centuries, in periods needed for malting a nree stages involved in the process century, and that savings are made in all stages,(say 1.8% N), destined for a vinegar factory, although the greatest benefits have been achieved 46-49% m/c may be preferred. Higher moisture in the germination stage levels induce faster modification but greater losses are incurred(Briggs, 1978). Anaerobic condi tions are dangerous as they favour fermentation by micro-organisms present. The ethanol pro- Traditional malting included a ditch steep duced can harm the grain. On the other hand followed by germination in heaps on the floor. It excessive aeration leads to chitting under water was a labour-intensive proc he heaps or and, consequentially, an undue rise in moisture couches'required frequent turning. It was also content. time consuming It is desirable to replace steeping water with Current practice varies according to the size fresh, between 1 and 4 times, as phosphates of operation and the preference of the maltster and organic compounds, including alcohol, accu- but self-emptying steep tanks have replaced the mulate and the microbial population grows ditch steep Vessels may be fat-bottomed or During the first steep dissolved oxygen conical-bottomed tanks. They have facilities for depleted from steep-water at a rate of l mg/ water filling and emptying, and compressed air kg per hour but it rises 10-fold by the third blowers provide both aeration and 'rousing and steep Complete depletion is possible within one mixing during the steep. Together, these pro- hour. Temperature is controlled to a degree cesses combine to remove carbon dioxide which by the water temperature to between 10 and accumulates as a result of respiration of grains 16.C and micro-organisms associated with them vigo There are many variations in steeping practice rous aeration immediately after discharging the including steeping in running water(Bavarian barley into the steep tank also serves to raise and the ' flushing regime in which immersions dust, chaff and light grains to the surface for are frequent but cover the grains for only a few removal. These are accumulated and sold for minutes. Modern steep tanks are filled with barley to a depth of 1.2 m. This increases to Aeration, damping and temperature have to 1. 8 m when the grain is swollen. The uniform be carefully controlled in order that germina- depth of flat-bottomed tanks provides for more tion occurs at the required rate and to the uniform aeration and coz removal than in conical required degree, For poorly modified traditional bottomed vessels pale lager, European 2-rowed barley needs Following steeping, the grain is transferred to steeping to 41-43%m/c, while for a pale-ale malt germinating vessels. This may be by ' wet-casting 4345%is appropriate For a high nitrogen barley whereby it is pumped in water suspension or
1686 1886 Germinate Kiln IO-35d 4-6d Steep 6-8d - 3-7d 8-28 d 3-6 d -
222 TECHNOLOGY OF CEREALS Turner boom Exhaust oir Drive/ Rail Rotating spirals F Plenum FIG 9.4 Diagrammatic section through a circular germination vessel. Source: Gibson 1989. Reproduced by courtesy of Aberdeen University Press, Ltd dry-casting after draining. If additives are to be Temperature and humidity are controlled by added it is convenient to do so during transfer. humidifying and refrigerating or warming the air These may include gibberellic acid and potassium passing through. Air volumes passing are of bromate.The former hastens malting, especially the order of 0.15-0.2 m/sec/tonne of barley if bruised grains are present, and potassium Temperatures of 15-19oC are common. micro- bromate reduces respiration and hence the rise processor control of conditions is commonplace in temperature that accompanies it It is also said ( Gibson, 1989) to inhibit proteolysis and control colour develop The danger of microbial contamination is high malting loss by reducing root growth s reducing as air passing with high humidity is ideal for ment in the malting grain, as well as growth of bacteria and fungi and nutrients are plentiful. As well as introducing health hazards Germination microbes gain preferential access to oxygen, thus inhibiting the germination and modification of Early mechanical maltings had rectangular the barley for which the system is designed. In germination vessels, but this was followed in due some plants the germination and kilning are but is limited to about 100 tonnes and has a high advantage of the microbes being killed by ls course by the drum, which provided ideal control carried out in a single vessel and this has the unit cost. Later the circular germination vessel heat of kilning. Cleaning the dry residue is easier was developed and capacities rose to 500 tonnes. than complete removal of the wet remains of Features common to all mechanical maltings are germinating grai an automatic means of turning the germinating grains and a means of aeration. Turning may be performed by rotating spirals that are moved Kilning slowly through the grain mass. In the rectangular The objectives of kilning are to arrest botanical vessels they move end to end on booms while in growth and internal modification, to reduce he circular type vertical turners rotate on a boom moisture for grain storage, and to develop colour or alternatively they remain stationary while the and favour compounds in the malt. Kilning is grain is transported past on a rotating floor. It is responsible for 90% of the energy consumption usual for aeration to be provided by air passing of the entire malting process unless a heat recovery up(usually) or down, from or into a plenum' is in use, when the proportion may be reduced to beneath the floor which is constructed of slotted 75--80% steel plates. The layout of a circular germination For kilning, ambient air is heated by the pre vessel is shown in Fig. 9.4 ferred fuel and passed under positive or negative
222 TECHNOLOGY OF CEREALS Drive / Ra i I Rotating spirals I Perforated Humidificatibn system floor (plus refrigeration if required) FIG 9.4 Diagrammatic section through a circular germination vessel. Source: Gibson 1989. Reproduced by courtesy of Aberdeen University Press, Ltd. 'dry-casting' after draining. If additives are to be added it is convenient to do so during transfer. These may include gibberellic acid and potassium bromate. The former hastens malting, especially if bruised grains are present, and potassium bromate reduces respiration and hence the rise in temperature that accompanies it. It is also said to inhibit proteolysis and control colour development in the malting grain, as well as reducing malting loss by reducing root growth. Germination Early mechanical maltings had rectangular germination vessels, but this was followed in due course by the drum, which provided ideal control but is limited to about 100 tonnes and has a high unit cost. Later the circular germination vessel was developed and capacities rose to 500 tonnes. Features common to all mechanical maltings are an automatic means of turning the germinating grains and a means of aeration. Turning may be performed by rotating spirals that are moved slowly through the grain mass. In the rectangular The objectives of kilning are to arrest botanical vessels they move end to end on booms while in growth and internal modification, to reduce the circular type vertical turners rotate on a boom moisture for grain storage, and to develop colour or alternatively they remain stationary while the and flavour compounds in the malt. Kilning is grain is transported past on a rotating floor. It is responsible for 90% of the energy consumption usual for aeration to be provided by air passing of the entire malting process unless a heat recovery up (usually) or down, from or into a 'plenum' is in use, when the proportion may be reduced to beneath the floor which is constructed of slotted 75-80%. steel plates. The layout of a circular germination For kilning, ambient air is heated by the prevessel is shown in Fig. 9.4. ferred fuel and passed under positive or negative Temperature and humidity are controlled by humidifying and refrigerating or warming the air passing through. Air volumes passing are of the order of 0.15-0.2 m3/sec/tonne of barley. Temperatures of 15"-19"C are common. Microprocessor control of conditions is commonplace JGibSnn, 1989). The danger of microbial contamination is high as air passing with high humidity is ideal for growth of bacteria and fungi and nutrients are plentiful. As well as introducing health hazards microbes gain preferential access to oxygen, thus inhibiting the germination and modification of the barley for which the system is designed. In some plants the germination and kilning are carried out in a single vessel and this has the advantage of the microbes being killed by the heat of kilning. Cleaning the dry residue is easier than complete removal of the wet remains of germinating grain. Kilning