Section of Gillaume’s Inclined Column StillFig.33.—Section of Gillaume’s Inclined Column Still.
Fig.33.—Section of Gillaume’s Inclined Column Still.
A distinctly modern type of still, though akin to the still shown in Figs.19and20, is the inclined column of Gillaume, shown in section in Fig.33and in full view in Fig.34. Gillaume in devising this form of apparatus had particularly in mind the distillation of thick washes, and the necessity of compelling a circulation of the wash.
Gillaume’s Inclined Column StillFig.34.—Gillaume’s Inclined Column Still.
Fig.34.—Gillaume’s Inclined Column Still.
The bottom of the inclined columnAis divided by lateral extending, upwardly projecting platesor partitionsaforming a continuous channel through which the wash passes from side to side and from top to bottom and then out through a regulator. The upper plate of the column has downwardly projecting partitionsbwhich with the partitionsaform a series of traps. The steam enters at the bottom of the column into a reservoir, and in order to pass upward is forced beneath each partitionband through the washer contained in the channels of the bottom. When it reaches the upper end of the column it has passed through a continuous series of wash-filled compartments containing a constantly moving current of wash.
The vapors from the top of the column pass off to the wash heater or to a concentrator.
In Fig.34is shown a form of Gillaume still designed to distill all sorts of liquids whether thin or thick. The wash is supplied from an overhead tank to a regulating tankKfrom which a pipekleads to a regulating tapm. The wash re-ascends into the wash heaterBand when heated descends by pipeFinto the uppermost compartments of the columnA. The vapor passes to the condenserB, by a pipeH, and the spent wash is discharged by a siphonC. In addition to the parts above referred to,adesignates entrance of wash into heater,bexhaust test tube,dsteam entrance tapGalcohol test glass,G′exhaust test glass,ovalve for regulating strength of spirit,Osteam regulator,pwater entrance tap,rexit tap, andDthe spent wash extractor.
The Gillaume apparatus is particularly valuable for the production of industrial or agricultural alcohol. It is claimed that it is easily understood and operated even by unskilled labor, while it produces a large proportion of alcohol of a high strength.
A view of a complete apparatus on a large scale is shown in the Fig.40in the chapter on rectification.
The product of the distillation of alcoholic liquors, which is termedlow wine, does not usually contain alcohol in sufficient quantity to admit of its being employed for direct consumption. Besides this it always contains substances which have the property of distilling over with the spirit, although their boiling points, when in the pure state, are much higher than that of alcohol. These are all classed under the generic title offusel-oil; owing to their very disagreeable taste and smell, their presence in spirit is extremely objectionable. In order to remove them, the rough products of distillation are submitted to a further process of concentration and purification. Besides fusel-oil, they contain other substances, such as aldehyde, various ethers, etc., the boiling points of which are lower than that of alcohol; these must also be removed, as they impart to the spirit a fiery taste. The whole process is termedrectification, and is carried on in a distillatory apparatus.
As before stated, the wash as discharged into the still consists of alcohol mixed with water and a variety of impurities from which the alcoholmust be separated. In order that the process may be better understood we will assume that a mixture of pure alcohol and water is to be operated on in place of the wash as above referred to. Distillation in this case is intended to deprive the water of its alcohol, the operation theoretically leaving water in one chamber and alcohol in another. This is accomplished by reason of the differences in the boiling points of water and alcohol. The alcohol vaporizes at a lower degree (173° F.) than water (212° F.) Thus the liquid at the end of the operation has been divided into two parts orfractions.
This, however, is not a clean division for the reason that while in the beginning the vapors contain a large quantity of the more volatile alcohol, at the end they will contain a large portion of the less volatile water. The whole of the alcohol will be separated in this manner, but it will still be mixed with some water and in order to again divide the alcohol from the water the first distillate would have to be redistilled until at last the water is reduced to a minimum or entirely eliminated, if possible.
But as it requires less heat to vaporize alcohol than water, so it also requires more cold to condense alcoholic-vapor than water-vapor. If then we pass the mixed vapors into a condensing chamber cooled to a certain temperature low enough to condense water-vapor but not the alcohol-vapor, then the water-vapor will fall down as water whilethe alcohol-vapor being uncondensed passes on to another chamber where its temperature falls to a point where it in turn condenses into liquid.
In intermittent distillation, as by the simple still, the vapors of mixed alcohol and water at first contain a great deal of alcohol and a little water, then more water and less alcohol, and then a great deal of water and hardly any alcohol. It may be asked: “Why not take only the runnings rich in alcohol and leave the others?” The answer to this is that if this be done thenallthe alcohol is not extracted from the wash and there is just that much loss. The solution of the problem is to get all the alcohol out mixed with the water that is inevitably with it and then redistill this result thus getting out (sifting away) some of the water, and again distill this result, and so on until only pure alcohol is left. This, however, is a very troublesome business and has been abandoned as a means of removing impurities such as water, the ethers, and fusel oil except by makers of whiskey, brandy and other beverage spirits, in favor of continuous distillation and continuous rectification.
It will be seen from what has gone before that there are two means of separating alcohol and water; one by an initial difference in heating and by a further difference in cooling or condensing.
It is on this foundation that the whole art of fractional distillation or rectification rests. While we have for illustration been considering a mixture of pure alcohol and water, the wash or liquid formedby the fermentation of grain, etc., contains a variety of ingredients of different boiling points, some more volatile than alcohol, some less. The fermented wash consists first of non-volatile or only slightly volatile matters, such as salts, proteins, glycerin, lactic acid, yeast, etc., and second, volatile bodies such as alcohol, water, various ethers, etc., fusel oils and acetic acid.
When wash is distilled in the ordinary simple or pot still, the first part to come over consists of the very volatile matters,—more volatile than alcohol even,—that is, the ethers mixed with some alcohol. This is known as the fore-shot or first runnings, and is collected separately. When the spirit coming over possesses no objectionable odor, the second stage has begun. This running would be of the alcohol proper, getting weaker and weaker, however, as the running continues and this would be caught separately as long as it is of sufficient strength. At last would come the weak spirit containing much fusel oil. It is to be understood, however, that there is no defined line between these divisions. They graduate one into the other. The first and last runnings in the old practice were mixed together and distilled with the next charge. When a strong spirit was required, rectification would be repeated several times. It is customary, however, with the improved modern apparatus, to produce at the outset spirit containing but little fusel oil and at least 80 per cent of alcohol. This is then purified and concentratedin the above manner and afterwards reduced with water to the required strength.
Another cause of the offensive flavor of the products of distillation is the presence of various acids, which exist in all fermented liquors; they are chiefly tartaric, malic, acetic, and lactic acids. The excessive action of heat upon liquors which have been distilled by an open fire has also a particularly objectionable influence upon the flavor of the products.
Rectifying StillFig.35.—Rectifying Still.
Fig.35.—Rectifying Still.
The first operation in the process of rectification is to neutralize the above-mentioned acids; this is effected by means of milk of lime, which is added to the liquor in quantity depending upon its acidity; the point at which the neutralization is complete is determined by the use of litmus paper. In the subsequent process of distillation, the determination of the exact moments at which to begin and to cease collecting the pure spirit is very difficult to indicate. It must be regulated by the nature of the spirits; some may be pure 20 or 30 minutes after they have attained the desired strength; and some only run pure an hour, or even more, after this point. The product should be tasted frequently, after being diluted with water, or a few drops may be poured into the palm of the hand, and after striking the hands together, it will be known by the odor whether the spirit be of good quality or not; these two means may be applied simultaneously.
The process of rectification may be carried onin the apparatus shown in Figs.35and36.Ais a still which contains the spirit to be rectified; it should be four-fifths full. The condenserEand the coolerGare filled with water. After closing the cocksLandI, the contents of the still are heated by steam, which is introduced at first slowly. The vapors of spirit given off pass, by tubesb, above each platea, of the series in columnB, and escape throughCandDinto the condenserE, where they are condensed on reaching the lentilsd d′, and return in a liquid state through pipefand connectionsg g′to the upper plates of the columnB. In these return pipes the liquid is volatilized, and constantly recharged with alcohol to be again condensed, until the water in the condenser is hot enough to permit the lighter alcoholic vapors to pass into the coilc c c, without being reduced to the liquid state. When this is the case, the vapors pass throughFinto the coolerG, where they undergo complete condensation. Great care must be taken that the heat is not so great as to permit any of the vapors to pass over uncondensed or to flow away in a hot state; and also to keep up a constant supply of water in the cooler without producing too low a temperature; the alcoholic products should run out just cold. The highly volatile constituents of the spirit come over first, that which follows becoming gradually purer until it consists of well-flavored alcohol; after this comes a product containing the essential oils. The more impure products are kept apart fromthe rest and re-distilled with the next charge. Some hours generally elapse before alcohol begins to flow from the cooler. The purest alcohol is obtained while its strength is kept between 92° and 96° Baume, and the operation is complete when the liquid flowing through the vessel marks not more than 3° or 4° Baume; it is better, however, to stop the still when the backing or “faints” indicate 10°, because the product after this point contains much fusel-oil, and is not worth collecting.
Section of Rectifying StillFig.36.—Section of Rectifying Still.
Fig.36.—Section of Rectifying Still.
In order to cleanse the apparatus—which shouldbe performed after each working—the stillAis emptied of water by opening the cockQ. The contents of the condenser are then emptied in like manner by opening the cockJ, through which they flow upon the plates in the columnB, and wash out essential oils which remain in them. These two cocks are then closed, and the doorUin the still head is removed. The water in the coolerGis then run by means of pipe into the stillA, so as partially to cover the steam-coil in the latter. After again securing the doorU, a strong heat is applied, and the water in the still is well boiled, the steam evolved thoroughly cleansing all the different parts of the apparatus; this is continued for 15 or 20 minutes, when the heat is withdrawn and the still left to cool gradually.
In the intermittent rectifying still above described the impure products are distilled with the next charge. In the apparatus as perfected and used in large distilleries or rectification plants, the division of the several products composing the phlegm or raw spirit is made at one time and continuously on the principle now to be described.
It was stated in the beginning of this chapter that the various impurities in alcohol, the ethers, the water and the fusel oils, have each their own vaporizing point and each their own condensing point. As this is so, they may be separated from each other and from the alcohol on the same principle as we have seen that water is separated from the mixture of pure alcohol and water; that is, byfractionation, as it is termed, or by “sifting out” one body from another.
Fractional Distilling ApparatusFig.37.—Fractional Distilling Apparatus.
Fig.37.—Fractional Distilling Apparatus.
Thus in fractional distillation, each condenser or retort in the apparatus shown in Fig.37, above acts as a sieve or trap, letting pass the most volatile substances but retaining those of a less degree of volatility. By passing the mixed vapor together through a good condensing medium the temperature of which is lower than the boiling point of the less volatile, but not so low as the boiling point of the more volatile the vapors of the less volatile liquid will be condensed, while the more volatile will retain their gaseous form. Thus by having a number of condensing mediums each one slightly lower in temperature than the other, the various vapors with their various points of volatilization will be successively condensed, allowing the passage of the more volatile vapors over to the condenser beyond.
If we had mixed gravel and sand and desired to separate the gravel into assorted sizes and get the sand by itself, we would pass the mass through a series of sieves of gradually smaller mesh. The first sieve of course would catch all the largest pebbles, the next in size would let all the second sized gravel through, and so on until the final sieve would have separated the coarse sand from the fine. In this figure of illustration, the coarse pebbles may be taken to represent the water and the fusel oils which are mixed and partly tend to rise with the alcohol, and the alcohol may be represented as the gravel larger than the sand, and the fine sand as the etheric vapors. If this gravel were forced upwardly through a series of sieves gradually growing finer, it would be analogous figuratively to the upward passage of the vapors through a distilling column composed of plates or chambers; the water and fusel oils would be retained in the lower portion of the column and continually sent back there; the alcohol would pass into the upper chambers of the column and the ethers or fore-shots would pass out from the very fine sieve at the top of the column.
The vertical chambers above each plate of the rectifying column are to-day used as the separate eliminating chambers referred to above. It has been found in practice that as before stated, each plate of a column contained upon it liquid of a certain temperature and above it vapors of a certain degree of vaporization. That is, in a continuouscolumn fed regularly by condensation from above and supplied with a constant flow of phlegm, each plate carries upon it a liquid of constant composition relative to the boiling point of the fluid on that plate. As many extractions may thus be made from the various plates as there are different liquids to be isolated. Thus by tapping different portions of the column, vapors of different degrees of vaporization are found and may be carried off and the phlegm be thus fractionated. In the case of one column the first runnings or fore-shot would be found in the upper portion of the column to which they would have risen by reason of their degree of volatility. The last runnings or oils, aldehydes, etc., would be found in the lower portion of the column still mixed with the spirit, while upon the plates of the middle portion of the column would be found the vapor of the alcohol freed from the fusel oils and from the,ethers.
It is understood, of course, throughout this description that the liquid being treated is not wash but phlegm; that is, the raw spirit containing the fusel oils, ethers, water and alcohol.
Fig.38represents a simple rectifying apparatus designed for small or medium sized plants, and manufactured by the Vulcan Copper Works Co., of Cincinnati. The still is upright, with a chambered column above it, of the usual type. The chambers are fitted with a vapor boiling pipe and cap and a drop pipe, and each is provided with cocks whereby it may be drained for cleansing.Above the column is a separator, comprising a casing containing a series of tubes. The vapor from the column circulates around the tubes through which passes a current of cool water. The condenser is of the same construction as the separator and is provided with a gage glass and a draw-off cock. The operation is the same as in other simple rectifiers; part of the vapor from the column is condensed in the separator and passes back on to the upper plates, while the more highly vaporized portions pass over into the condenser.
Rectifying Apparatus with External Tubular CondenserFig.38.—Rectifying Apparatus with External Tubular Condenser.
Fig.38.—Rectifying Apparatus with External Tubular Condenser.
The diameter of the still is large relatively to its depth so as to yield an economical and at the same time highly effective distribution of heat through the charge. This also affords an extended boiling area from which the vapor rises evenly and regularly, thus ensuring conditions peculiarly conducive to produce the best fractionating. The floor space required for this still and others of the same character built by this company is very compact and excessive weight on the top floor of the building is dispensed with.
We have shown in Figs.39and40two forms of rectifying apparatus, one a twin column Barbet rectifier and the other a rectifier of the Gillaume type combined with inclined column still.
In the twin column apparatus, Fig.39, the first column or clarifierAreceives the raw phlegm and accomplishes the elimination of ethers. The clarified phlegm passes then to the second columnwhere the alcohol is separated from the last runnings or fusel oil. In other words, the phlegm or impure raw alcohol is only raised to such a temperature in the first column as to drive off the very volatile constituents such as the ethers. These therefore pass off at the top of the first column into the condenserC, the retrogradation or condensed alcohol being returned toA, while the boiling phlegm taken from the middle of the column and still containing the aldehydes, oils, etc., is conducted by a pipeEto the second columnBwherein the last runnings or amylic oils, etc., are separated from the purified spirits.
Twin Column Barbet RectifierFig.39.—Twin Column Barbet Rectifier.
Fig.39.—Twin Column Barbet Rectifier.
The vapors in this column are carried to the condensersDandFand from there to a refrigeratorG. The fusel oils are extracted from the plates slightly below the center of the column and are carried to an oil concentrating apparatusH.
In the most complete forms of apparatus used to-day, there is a variation of this construction. The first runnings, middle runnings and the last runnings are each led off from the main column to separate coolers, condensers, etc., and the purified result from each of these columns is in turn led to a trunk rectifier common to all where the product is redistilled and entirely freed from impurities. This gives a very high grade of alcohol by a process practically continuous. At the same time the impurities are not returned to the first or main column to contaminate the vapors therein and add to the amount of fusel oils contained onthe lower plates. In construction of this character there is a very large saving in the cost of the fuel and the result is much better in every way.
Gillaume’s Rectifier and Inclined StillFig.40.—Gillaume’s Rectifier and Inclined Still.
Fig.40.—Gillaume’s Rectifier and Inclined Still.
Fig. 40.—Guillaume’s Direct Distillation-Rectification Apparatus for “Agricultural” Distillations.
In this apparatus the still proper is of the form heretofore described on page78. The liquid to be distilled enters at the top of the inclined columnAand descends to the base thereof. The alcoholic vapor rises through the column and passes off from the head thereof into the rectifying column. At the head of the columnAit has a strength of about 40° to 50° F. The columnCis supported upon an accumulating reservoirVwhich acts to regulate the flow of the phlegm through the rectifying column and prevents too great an exhaustion of the plates of the column. It acts as a reservoir to contain any excess of phlegm or to supply an additional amount of phlegm to the plates when they have become nearly exhausted.
The oils or products of the last running accumulate at the base of the column, and are carried off to their special refrigeratorQ. The alcoholic vapors concentrate while rising in the column and quickly attain a strength of 92° or 94° F. At a height within the column corresponding to the plates whereon alcohol of that strength is to be found, there are provided three tapsuwhereby the middle runnings or medium grade of alcohol may be drawn off, which have a maximum concentrationof 92° and 94° F. Above these middle plates the alcohol vapors are completely separated from the products of the “tail” that is the aldehydes, amylic oils, etc., and at the upper portion of the column there is found the condenserKwhich separates the products of the head; that is the first runnings from the alcohol which has passed over with such products to the condenser. The alcohol so separated is completely rectified in the column of final purificationDand the finished alcohol is cooled in the refrigeratorObelow the column of final condensation. In this apparatus the gauge glasses which regulate the exit of the various alcohols and mixtures are controlled by taps having verniers or scales whereby they may be very carefully adjusted, to regulate the relative proportion of the various products. This apparatus is able to produce about 75 or 80 per cent. of first-class alcohol, 10 to 15 per cent. of middle class alcohol, and 5 per cent. of ethers and 5 per cent. of fusel oils, the alcohol produced being about 96° Cartier.
The alcohol is thus obtained in one single operation and with, it is asserted, only a very small loss in rectification. The apparatus is claimed to be so simple that it may be operated even by unskilled farm labor. It is also claimed that purification by chemical treatment or filtration is unnecessary with the Guillaume apparatus. It may be stated, however, that the Guillaume system has many opponents.
The capacity of the rectifying apparatus has a good deal of influence upon both the quantity and the quality of the spirit obtained. Besides being much more difficult to manage, a small apparatus will not yield so large a proportion of spirit as a more capacious one, nor will its products be of equally good flavor. The proportion of alcohol which may be obtained from a successful rectification is very variable; it depends upon the nature of the spirit rectified, the method of extracting the sugar, and the manner of conducting the distillation; it will also be in inverse proportion to the quantity of fusel-oil contained in the raw spirit. The average loss of pure alcohol during the process of rectification is generally estimated at about five per cent.
In addition to the rectifying as above described, alcohol may be further purified by filtration through charcoal, by chemical means or by electrolysis. The last two methods have not so far been successful. The chemicals used merely act to disguise the disagreeable taste or smell of the spirit and do not really purify. They but substitute one impurity for another. The agents used are many—sulphuric and nitrate acids, soaps, oils and fats soda, lime and potash have each and all been tried, but with no permanent success. As agents for disguising the taste of new and raw spirits, alcoholic extracts of fruits have also been used.
Purification and aging by electricity has been tried many times and in many different forms, but so far has not been commercially practicable.
Filtration still remains the best and simplest adjunct to the rectifier. In small plants, a filter bed several feet in thickness of bone black or beachwood or charcoal is used, laid upon a foundation of gravel in a filtering tank. In the larger plants a series of these vats is used, the charcoal being used in lumps varying from ¼ to ½ inch in diameter. Two different views of the purification by charcoal are held—one that the charcoal purifies by chemical means, the other that it is purely a physical filtration agent. After filtration the charcoal must be steamed to recover the spirits retained therein and should be heated to a red heat every now and then to cleanse and regenerate it.
Wheat, oats, rye, potatoes, and other amalyceous or starchy materials contain starch insoluble in water and to render it soluble, and to change the starch to maltose they must be mashed with a certain small proportion of malt,—or grain in which germination has been artificially induced and then interrupted at a certain stage. This increases the diastase contained in the grain so germinated, and this diastase is able to transform starch into soluble form. Hence, malted grain gives lightness and liquidity to the wash, and prevents the starch falling to the bottom of the mash tub or “back,” and also prevents the starch falling to the bottom of the still and consequent burning.
While all varieties of grain including rice are suitable for the preparation of malt, barley is preferred to all others, and is most commonly used.
The best barleyfor malting is that having the following characteristics; a thin skin; a mealy interior; grains of a uniform size; of the greatest weight; which has been stored for three months. Barley on harvesting has but slight germinatingpower. The reason for the uniformity in the grains lies in necessity of a uniform steeping of the grain so that the period of germination shall be the same for the whole mass.
Like all materials for distillation, the barley should be thoroughly cleaned of impurities—not only dust, seeds and weeds, but fungi and bacteria.
This may be partly accomplished in the ordinary fanning mills, usual on farms, but a better machine would be a “tumbling box” of wire mesh. This is inclined, so that grain put in the upper end, will pass downward to the lower, being thrown about as the box or cylinder is rotated. The dust, seeds, etc., fall through the meshes of the wire as do the smaller grains. After this cleaning, the barley should be thoroughly washed. This may be either done in the steeping vat itself—and the water afterwards drawn off—or in special machines. If the barley be allowed to soak in water for a day or two, the later washing will completely cleanse it. This preliminary cleaning is most important as impurities reduce the germinating power of the grain, as well as introduce bacteria inimical to fermentation.
Washing in some instances is done by forcing compressed air into the steeping tub, thus violently agitating and swirling the water therein, and washing away the impurities. Another method is by passing the steeped grains along a trough supplied with moving water, the trough being provided with rotary agitators. Any fairly ingeniousmechanic could devise a capable cleansing machine. Care being taken that it shall not injure the grains.
After cleansing, the barley should be steeped. For this purpose tanks of metal or cement are to be preferred to wood. All vats should be kept thoroughly cleaned by frequent scrubbing with lime water.
The barley placed therein should at all times be entirely covered with fresh water to a depth of a few inches, and for the first few hours the grains should be carefully stirred in order that no grain should escape wetting. At the end of that time the still floating grains should be removed.
In 36 or 48 hours the grain will usually be sufficiently steeped,—but this varies with weather conditions. The warmer the water the quicker the steeping, and in winter proper steeping may not be accomplished before four or five days.
A simple test is to rub the grain strongly between the hands, If it is entirely crushed, and no solid matter is left it has been steeped sufficiently. Barley should be capable of compression lengthwise and the hull should become easily detached. It should be easily bitten, and not crack under the teeth. In order to prevent fermentation in summer, it is well to renew the water a few times during steeping. Over steeping is worse than under steeping.
After the barley is in proper condition the vat or tank is opened and the water drained away.The draining should be complete, and therefore the grain should be left to drain about 12 hours.
Germinating.The grain is now taken to the malting floor. In practice it is well to locate the steeping vat above the malting floor, so that the steeped grain may be run down on to the floor without inconvenience.
It is best to first spread the grains out on the floor to a depth of a few inches in order that it may somewhat dry out. This is not necessary when it has not been steeped to a great extent.
After 10 or 12 hours of drying, the grain is placed in a heap until warm to the touch, which may occur in from 12 to 24 hours. It is then disposed in a layer from eight inches to 20 inches thick. This is called the “wet couch.” The lower the temperature the thicker the couch should be. It should be turned every six or eight hours in this stage.
The heat so germinated after 25 or 30 hours produces at the end of each grain a small white rootlet. The grain in the middle of the layer is the first to sprout, as it is the warmest, hence the couched grain should be frequently turned so as to give all the grains a uniform heat, and a uniform germination. At this period the grains beneath the surface are dampish to the touch.
The height of the couch is now successively lessened to layers of from six to two inches called “floors,” the height of each floor of course depending on the temperature, as before.
It is to be understood that the growing grain requires both dampness and air, hence the “floor” should not be thinned so rapidly as to deprive it of moisture, and the barley should be turned at least twice a day to give each grain a proper aeration. During this period the small white rootlets or radicals should be white and shiny. If they begin to fade, it is a sign that they lack water and the grain should be sprinkled. Germination usually requires from a week to ten days, or sometimes two weeks, depending on the previous steeping, the quality of the grain and the temperature. When the fibers or rootlets of the grain are about equal to the length of the grain, germination is complete.
It used to be considered that malt was in its best condition in eight or ten days. To-day, however, “long malt” is used,—requiring a germinating period of twenty days, being frequently moistened and turned during this time, and the temperature being kept at 65° F. This malt is very strong in diastase.
The effect of germination is to produce a change particularly favorable to mashing. The barley becomes sweetish, the gluten is partially destroyed and what is left is soluble. Thus the fecula or starch is set at liberty and free to be acted on by the yeast used in fermenting.
March is the best month in which to malt; and while the malt is best used immediately, it can not be kept in its green state and must be therefore dried for future use.
Drying.This is accomplished either in the air of a warm, dry room in hot weather, or by means of a drying kiln. In the first process the malt is spread in a thin layer and frequently turned. In the second the grain is spread out in a layer from eight inches to a foot thick on the grain floor of the kiln.
Beneath the grain floor a fire is maintained. In the beginning the temperature of the drying floor should be about 85° F., but this is increased gradually to about 104° F. until most of the moisture has been removed. The heat is then raised to from 120° F. to 130° F., thus completely drying the grain.
The germinated green or dried barley is called malt. It is of good quality when the grain is round and flowery; when it crumbles easily and when its taste is sweetish and agreeable. Pale malt or that which has been hardly altered from its original color is the best for distillation.
Before the malt can be used it should be screened so as to remove the rootlets.
Two hundred and twenty lbs. of barley should yield from 275 to 350 lbs. of green malt, about 200 lbs. of air dried malt, and from 175 to 190 lbs. of kiln dried malt.
In large plants malting is now so carried on that the steeping germination and drying are all accomplished in one vessel or container, by one continuous operation. This vessel is commonly in the form of a drum of sheet iron, revolving at a very slow speed. Moist air is introduced and thecarbonic acid laden air withdrawn. After germination the malt is dried by passing in dry air at the proper temperature.
As these systems are only adopted to large distilleries, using expensive machinery, further reference to them is not considered necessary in this volume.
Previous to use the malt must be finely ground or crushed either before or after mixing with the materials to be mashed. It is not necessary or advisable that the malt be reduced to flour. The use of malt with other materials in order to form a fermentible mash, will be considered in the chapters on specific mashes.
In certain countries, as for instance Germany and France, potatoes form the greatest source of alcohol, particularly for industrial purposes. With the possible exception of corn and beets they will probably be most used in America.
The best potatoes for distilling are those which are most farinaceous when boiled. In other words, those which are “mealy” and most appetizing. These give the largest yield of alcohol per bushel. The best season of the year in which to use potatoes is from October to March, when they germinate.
The potatoes should be kept in dry cellars, and at even temperatures, warm enough to prevent freezing and yet not so warm that they will rot or sprout. Diseased potatoes may however be used, if they have not been attacked by dry rot, though they are not so easily worked. Frosted potatoes may be also used, but they must not have been completely frozen.
Before being steamed, the potatoes should be washed, either by hand or by a machine, care being taken to remove all stones, clods of earth,and other foreign substances which might impede the subsequent operations.
There are three main methods of saccharifying the fecula or starch of the potato. The first and most important by reducing the tubers to a pulp, and malting the entire mass. The second and third, by rasping the potatoes and so separating the fecula or starch grains from the mass, and then making a thin liquor or wash containing this fecula.
Originally, in the first process, the washed potatoes were submitted to the action of boiling water, but later cooking by steam at a temperature of 212° F. was used, as being much more convenient to handle and more effective in action. The object of steaming is to break the coating and reduce the contents thereof to a pasty condition, wherein the starch is more effectively acted on by the malt and yeast. Ordinary steaming does not, however, render the pulp sufficiently pasty; some of the starch remains undissolved and is lost, hence in the modern practice, steam is turned into the steaming vat under a pressure of three or four atmosphere (45 to 60 lbs. to the square inch).
High pressure steaming will be later described but the simple and older method of mashing and apparatus therefor, used prior to 1870, was as follows:
Fig.41shows a section of a steaming vat. This consists of a conical wooden tubHprovided at its top with a suitable coverOhaving a trap or doorPfor putting in the potatoes. This as shown, consists of a hinged lid, having a buttonpor other fastening means. This lid and cover should be of course steam tight, and it would be better to have it clamped down by a screw clamp than held by a button.
Somewhat above the bottom of the vat, a steam inlet pipeIenters, connected at its other end by a couplingiwith a suitable steam generator (see Fig.43), Preferably the outlet of this pipe is screened by a perforated plateMso that it may not be clogged by the pulp. It is also best that a filling piece be placed at the junction of the bottom with the sides in order that there be no sharp corner from which the pulp may not be easily cleaned out.
Steaming Vat for PotatoesFig.41.—Steaming Vat for Potatoes.
Fig.41.—Steaming Vat for Potatoes.
The bottom of the vat may either have a discharge door at the side as in Fig.44or at the bottom, as in Fig.41.
An under side view of the latter construction is shown in Fig.42. The bottom of the vat is made in two parts or doorsJ K. These are held closed by a transverse barLinserted at its end into a stirrupl′and supported at its other end by a buttonl, or other means.