BREWING PROCESSES Broadly speaking there are two main brewing processes de noted by the terms "top" and "bottom" fermentation respec tively. They differ in that the yeast rises to the top of the wort after fermentation and can be skimmed off in the former or settles to the bottom of the fermenting vessels in the latter. They also differ in that fermentation is carried out at tempera tures ranging from about 58° to 7o° F in the top fermentation process and from about 4o° to 55° F in the bottom fermentation process. It is also customary to store the beer produced by the latter process for some weeks or months in large "lager" casks or tanks in cellars kept at about the freezing point of water. In consequence, it is generally known as the "lager" process and the beer as "lager" beer. In England almost all the beer produced is brewed by the top fermentation process, only about half a dozen firms brewing lager beer. On the Continent and in most other countries lager beer has to a very large extent displaced top fermentation ale. The system of mashing also differs in typical top and bottom fermentation breweries. The former use an infusion system, the latter a decoction process and in view of this difference there are differences in detail in malting prac tice, and in the characteristics of the malt employed in the two processes.
The malt is hoisted to the top floor where it may be screened and graded. From there it is then conveyed to the malt mill usually by way of an automatic weighing machine. Modern malt mills are designed not to grind the malt to flour, but to separate the internal part of the grain as completely as possible from the husks, grind it no finer than is necessary for complete extraction in the mash-tun and mix the "grits" and meal with the husks in a homogeneous "grist." The grist, with which any flaked material used is intimately blended, passes to the "grist-case" and thence to the "mashing machine" in which it is mixed with hot water of nicely adjusted temperature, drawn from the "hot liquor tank." From the mash ing machine the thick mash of malt and water flows to the "mash tun." This vessel is usually constructed of wood, iron or copper and is placed in most cases directly under the mashing machine above which is located the conical bottom of the grist-case. Inside the tun is a sparging apparatus consisting of pipes which are caused to rotate by the flow of water through fine holes in their sides. The water sprays every part of the "goods" in the tun and washes the wort from them after mashing is completed. The mash-tun has a gun-metal or bronze false bottom pierced with slots or holes designed to hold back the "grains" while the wort is running from them through "spend pipes" in the bottom to the "taps." It is also filled with rakes mechanically driven round in the mash to ensure thorough admixture. They are omitted in some mash-tuns, reliance for mixture being placed on the mashing machine. In other plants, without mashing machines, they may be used to mix the grist and water in which case they are sometimes replaced or assisted by a "propeller." The mash-tun is lagged and covered, sometimes with a copper dome as in the figure which is from a photograph of the mash room in a modern brewery. There are means for raising the temperature of the mash by an "underlet" or inflow of hot liquor through the bottom and in many cases an elaborate installation of thermometers for temperature control. After mashing is completed the spent grains are removed usually through grains slides in the bottom of the tun.
The object of mashing is the production of "wort" containing suitable proportions of fermentable and unfermentable "ex tract" from the grist. The extract is derived partly from the soluble carbohydrate and nitrogenous constituents of the malt, but also in larger part by conversion of its starch into soluble substances. As the character of beer depends so largely on the amount and proportions of these in the wort, the mashing pro cess is of fundamental importance and most carefully controlled. In the "Infusion mash" most commonly employed for top fermentation beer the "initial heat" or temperature of the com pleted mash usually varies from about to F between which temperatures the diastase of the malt is still active, and at which the modified starch of the malt is brought into a suita ble condition for its converting action. These temperatures are rather too high for much proteoclastic, or protein digesting action to take place and this has largely been assured by the system of malting adopted so that the wort shall contain, in addition to soluble carbohydrates derived from the starch, an adequate amount of dissolved nitrogenous substances. If high tempera tures are employed they are maintained throughout the mash. If low initial temperatures are adopted the heat is raised after about half an hour by about 5 degrees, generally by an "under let" of hot water, more easily and fully to convert any "steely" ends or unmodified starch in the malt. After a rest of about I to 11 hour the wort is run off and the grains extracted as com pletely as possible by "sparging" on water of rather higher tem perature than that of the mash. After the wort is drained from the mash-tun, the "grains" are removed and form a valuable cattle food (q.v.).
The chemistry of the changes which take place in the mash-tun is extraordinarily complex and is not yet fully understood. It consists essentially of the conversion of insoluble colloid con stituents of the grain, of which starch forms the major part, into soluble substances. The starch and proteins of the grain have both been "modified" during malting (q.v.) : the starch in such a way as to render it more readily amenable to the action of the diastase of the malt. It is generally recognized that at least two enzymes are included in the term diastase. Broadly speaking, it may be said that the chief products of the saccharification of starch are the fermentable sugar, maltose, and unfermentable dextrin; but there are other potentially fermentable substances of more complex molecular structure than maltose but less com plex than dextrin, among which two malto-dextrins have been char acterized. These substances are dissolved in the wort and their relative proportions vary with the conditions in the mash-tun, largely as the latter influence the energy of the diastatic action or conversion. Among these influences are the restricting effect of higher temperatures and alkaline salts in the water on the one hand, and the accelerating effects of slight acidity, dilution, etc., on the other. These with the nature of the grist, in regard to its diastatic power, modification and character of the malt and pro portion of raw or prepared grain determine the nature of the wort and ultimately of the beer. Very careful co-ordination of malting and mashing processes are therefore demanded. Restric tion of diastase, consequent on high kilning heats, can to some extent be counterbalanced by low mashing heats, while higher mashing heats, and those used in the sparge, can be used to bring undermodified malt into a condition suitable for conversion, pro viding the saccharifying power of the malt is sufficient and not unduly crippled by those high temperatures. The hydrolysis and solubilization of certain of the proteins of barley is as important as the conversion of the starch in brewing. The proteoclastic enzymes are however inhibited at considerably lower temperatures than those which prevent diastatic action and their activity in the usual infusion mash is very much restricted. Reliance must, therefore, be placed on the malting process for much of the neces sary degradation. Temperatures of Ioo° to IIo° are required to determine much proteoclastic change in the mash-tun and at times such digestive temperatures are adopted in the infusion system.
The result of these changes, in malting and mashing, is compar able to that undergone by starch and is the production from pro teins of colloidal degradation products of high complexity, pep tones, etc., and a greater or smaller amount of simpler nitrogen compounds of which the amino-acids and amides are typical. Malting barley may contain between 6.5 and 12% of proteins, on which, to a large extent, the flavour, etc., depend. Moreover, fermentation cannot go on satisfactorily without a sufficient pro portion of assimilable nitrogen for the needs of the yeast. Excess in quantity or unsuitability in composition is harmful and leads to difficulty in fermentation and lack of brilliance in the beer.
When flaked cereals or raw grain are used in addition to malt, variations are made in the mashing process. The starch of flaked maize or rice is gelatinized during the process of flaking and is readily converted in the mash-tun by the diastase of the malt, and the only modification in process required is the careful mixture of the flakes with the grist. If unmalted grain is used in the form of "grits" its starch must be gelatinized before mixing with the malt which provides the diastase for its conversion. This is done by heating with water, sometimes in a "converter" under pressure at a temperature somewhat higher than the boiling point of water and sometimes in an open cooker between 190° and 212°. In either case a small amount of malt is usually mixed with the grain to assist gelatinization. The gelatinized grain is pumped into the mash-tun, where the main mash of malt has stood at least half an hour, care being taken that the temperature of the mixture is not above that suitable for the complete sac charification of the starch. Mash-tun rakes or propellers are used to mix the two mashes. It may be noted that the proteins of raw grain are not acted upon by the diastase of malt. Modern improvements in mashing plant and processes are designed to extract the largest quantity of desirable substances from the grist and to ensure fullest control of the conditions of temperature, etc., which influence conversion. Various processes other than that adopted in the mash-tun with false bottom have been sug gested for separating the wort from the grains, among them cen trifuges and filters. The latter in the form of filter presses with cloth filters have proved suitable and are used to a considerable extent in Continental Europe but have not been adopted to any extent in England. It is claimed for the "Mash Filter" that a more complete extraction can be obtained with less washing liquor, and more quickly than with the mash-tun and sparge, but the trouble with the cloths, and the readiness with which the well-modified malts used are extracted has restricted their adop tion in conjunction with the infusion mash.
The separation of the wort from the hops previous to cooling is a stage of considerable importance in that the insoluble sub stances separated in the copper must be removed as perfectly as possible. This is effected in most breweries in the "Hop back," a large iron or copper vessel with perforated false bottom to which the wort runs from the coppers. In it the hot wort is al lowed to stand for a short time for the hops to settle down and form a filter bed through which the "hopped wort" is drawn off or pumped to the coolers or wort receiver. The hop back is fitted with a sparge to wash out wort otherwise retained in the "spent hops" which are afterwards used in the manufacture of cattle f oods and in manures.
During fermentation these cells increase in number by budding, deriving their nutriment from the wort and breaking down the sugars contained in the latter into almost equal parts of alcohol and carbonic acid gas. As added to the fermenting vessels the yeast or harm is a liquid mass of creamy consistency. During the earlier stages of fermentation there is a great evolution of carbonic acid gas. At a later stage the yeast, increased three to five-fold by its vegetative growth, rises to the top of the vessels in top fermen tation, and is removed and used again for succeeding brews. The excess over that required for this purpose is pressed and in some breweries pressed yeast is used for "pitching." The ale filtered from it is returned to the fermenting vessels while the pressed yeast is sold to distillers or used for making cattle foods or yeast extracts for human consumption. Very little is now used for baking as it is not so satisfactory for that purpose as specially prepared baker's yeast (q.v.).
There are several systems of fermentation employed in top fermentation breweries, differing in the construction of the vessels in which the process is carried out and in the means adopted to separate the yeast from the beer. It is of interest to examine the ancient brewery of Queen's college, Oxford, to gain an idea of the manner in which these systems have developed. There are few, if any, breweries remaining in the country of equal antiquity to that at Queen's and probably the process carried out is the same as that which has prevailed for hundreds of years, with very few modifications, such as the adoption of thermometers. The mash-tun has no false bottom. The wort is pumped to the copper by means of a i6th century lead and wood hand pump, is run down a wooden trough to the surface cooler, where it remains for several hours. There is no refrigerator but a recent addition is a copper coil in one of the surface coolers to hasten cool ing. The wort at 66° then runs to a wooden fermenting round, where the yeast is added and in which there is no means of con trolling the temperature. There it remains for a night and a day while fermentation progresses. When this process slackens the yeast begins to come to the surface of the wort and the cleansing stage follows, during which the new yeast is removed. In this old system, still employed in many old small top-fermentation breweries in northern France, the cleansing takes place in casks. In this particular brewery, there is no means of running the wort out of the fermenting vessel, and it is ladled into the casks through a "tun-bowl" placed in the bung-hole. The casks after filling are rolled to a cellar and there set up over a wooden trough with their bung-holes open. Through these the yeast works out, together with beer, and runs over the sides of the casks into the trough, from which the beer is returned to the casks. When fermentation is completed the casks are filled up from a cask specially retained for that purpose and, after settling, the beer is transferred to storage casks or allowed to remain in the cleans ing cask until bright and ready to drink.
Fermenting vessels are now frequently constructed so that, after excise regulations are complied with and the charge is taken, they can be completely closed or covered with a dome in order that the carbon dioxide evolved during fermentation may be col lected. The gas is pumped off and stored in large containers usually at a pressure of about 2 5olb. per sq.in. for use in the brewery itself or the bottlery. The gas collected in this way, con taining over 99.8% of carbon dioxide is valuable for carbonating bottled beer. Large quantities of fermentation gas are also lique fied and sold to mineral water factories.
Among the most important technical improvements of recent years are those connected with the purity of the yeast and its suitability for pitching. Many breweries are fitted with yeast backs frequently of slate, beneath the fermenting vessels. In the dropping system they form the lowest of the three floors of ves sels. In these the yeast is drained of the accompanying barm-ale. They are, however, more or less exposed to contamination and frequently movable receivers are used in which all yeast required for pitching is removed to a room designed to be kept scrupulously clean and at a suitably low temperature. The Scott system is a development of this. The yeast is removed from the fermenting vessel by gravity or suction to closed aluminium tanks on wheeled carriages or run-ways. From these the yeast is forced by com pressed air through filter presses and separated from the barm ale. By this system, the yeast is kept from atmospheric con tamination ; and the accompanying beer is rapidly separated and returned to the fermenting vessels.
Fermentation is carried out in cellars maintained at a low temperature by refrigerating machinery with brine or direct ex pansion coils or by a current of cold air. The wort is pitched at temperatures varying between 41° and 50° rising during fermenta tion, which takes a period of 9 to 12 days, some five degrees above these temperatures and being finally cooled to between 36° and 45° before transference to the storage or "lager" casks. The yeast employed falls to the bottom of the fermenting vessels instead of rising to the top. The lager casks used to be made of wood, and varied in capacity from 20 to 5o barrels, but glass lined steel tanks, and sometimes cement tanks, of several hun dred barrel capacity are now replacing the old wooden casks. These are arranged in cellars maintained close to the freezing temperature and the beer is kept there for periods varying from a few weeks to several months. "Krdusen" or fermenting wort is sometimes blended with the stored beer to increase the condition. Deposition of yeast and proteins takes place in the lager casks and, owing to the slow fermentation which goes on therein and the greater solubility of carbonic acid gas at low temperatures, the beer develops a very fine creamy condition. After storage it is filtered to the trade casks. Lager beers of similar gravity to English beers are usually fermented to a less extent and conse quently contain somewhat less alcohol and more unfermented extract. They are less heavily hopped and more highly charged with carbonic acid gas. The beer in cask must be kept colfl and served rapidly. Top-fermentation beers are typically more stable on account of the larger alcohol content and greater hop rate.
Types of Lager Beer.—In Continental Europe several brew ing centres have become celebrated for distinct types of lager beer, of which three may be specially mentioned. These are the dark, sweet, full-flavoured Munich beer, the pale, delicately hopped drier beer for which Pilsen is famous, and a medium pale type represented by that of Vienna. The Dortmund beer is another type of pale lager, with less pronounced hop flavour than that of Pilsen. Typically they vary in strength between 12-i to 142 degrees Balling, equivalent to 1,050 to 1,058 specific gravity. These type names, together with others derived from brewing centres such as Budweiss or Wurtzburg, are frequently applied to corre sponding beers brewed elsewhere.
A strong lager beer of 1,057 original specific gravity, or 14 degrees Balling, would contain on an average about 6% of resid ual extract and 4% of alcohol; lighter lagers brewed at io or 12 degrees Balling, correspondingly less.
Many modifications of the typical German "lager" system have been developed, largely in America, and are used elsewhere. Where maize or rice are available and permitted, they are used in the form of flakes or grits in varying proportions, from io to 40%, with the malt. Saturation with carbonic acid gas, largely derived from the fermenting wort itself, has in many places taken the place of krausen for producing the condition required. Some what higher fermenting temperatures, with a correspondingly shorter time in fermenting vessels, were frequently used in America than is customary in the German breweries.
The sale of lager beer in bottle has greatly increased of recent years. In the large breweries in Copenhagen over 95% of the out put is bottled in magnificently organized bottling halls fitted with automatic machinery. In order to ensure purity and stabil ity, an increasing proportion of bottled lager beer is pasteurized, particularly for export and consumption in hot countries. Pure Yeast.—Among the greatest advances in brewing of recent years has been the introduction and use of pure yeast. Pasteur showed that many of the diseases of beer were caused by bacteria and, later, Hansen proved that others were due to the presence of varieties of yeast other than the normal brewing yeast. This naturally resulted in endeavours to obtain yeast which should be free from these organisms. Hansen's method of producing a mass of yeast from one single cell, selected because it was of desirable type, was first adopted on a large scale in the Old Carlsberg brewery in 1881, and is now very frequently installed in lager breweries. Sufficient culture yeast of strict biological purity is grown up in this apparatus to pitch the brewery fermenting ves sels and the use of pure yeast results in greater certainty and regularity of produce. It has not hitherto been found possible to make use of pure yeast in top-fermentation breweries largely on account of the secondary fermentation required for some beers and carried out in the cask before sale and on which the character istic flavour of the beer depends. The secondary fermentation is largely brought about by other varieties of yeast. To-day secon dary fermentation is sometimes eliminated and it is possible that pure yeast may be adopted in time in top-fermentation beers also.