Hvdrolvsis and Catalvtic xidation of Cellulosic Materials. J
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Hydrolysis of Natural, Regenerated, and Substituted Celluloses R . F. NICKERSON Mellon Institute, Pittsburgh, Penna.
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HE existence of long, unbranched, homogeneous chains of anhydroglucose units as the primary structural elements of cellulose is well established. Kevertheless, many cellulosic materials, particularly the natural fibers and nonsubstituted derivatives, are more or less heterogeneous in character. This heterogeneity is structural and stems from the fact that the constituent anhydroglucose chains occur in both crystalline and amorphous forms. X-ray studies have yielded considerable information on the crystalline fraction (crystallites), but for various reasons the amorphous fraction has received little experimental attention. This paper presents quantitative data obtained by a new method on the hydrolysis of some common cellulosic materials. From these data are derived estimates of the relative percentages of amorphous cellulose. The natural cellulosic fibers are known to be more highly organized in structure than materials derived from them. The structural organization, particularly a t the submicroscopic level, merits attention because the natural fibers are widely used in an intact condition and because cellulosic derivatives of various kinds are modifications of the native form. Of the two types of products derived from native cellulose-namely, regenerated and substituted cellulosesthe latter are unique in properties and behavior as a result of substituent groups which block some of the hydroxyls and introduce steric effects. Consequently, the ensuing discussion does not apply to the esters and ethers of cellulose. There is little doubt that the structure of purified cellulose is heterogeneous. It contains dense, discontinuous crystallites disposed in an amorphous surrounding medium. The recent work of Whistler, Martin, and Harris (26,B7), Sookne and Harris @ and Kickerson ?I) and , Leape (16) indicates that this medium is not a pectinous substance as has been suggested (5). The type of structure discussed in recent summaries by Kratky (8) and Mark (1%)seems to be more consistent with the chemical behavior of cellulose and with the mechanical properties of native cellulose in the form of cotton fibers (14). I n this concept cellulose is regarded as composed entirely of anhydroglucose chains, identical in composition and structure, which cohere laterally in a periodic manner to produce crystallites ( 9 ) . The amorphous regions surrounding these crvstallites are noncohesive networks of such chains. The lharacteristics of the amorphous chain network are vastly different from those of the similarly constituted crystallites. The investigations of Kat2 (71, Farr (41, %son @ 1 ) , and Conrad and Berkley ($1 that water
aqueous solutions do not alter the x-ray diffraction pattern of the crystallites. The experiments of Reeves and Thompson (19) indicate that about one third the theoretically possible methoxyl content may be introduced into cotton fibers with little apparent change in the original structure or x-ray diagram, provided some moisture is present. Staudinger and Sorkin (IS) concluded from viscosity measurements that acid hydrolysis has little further effect on chain length when the latter has been reduced to 150-200 anhydroglucose units, the apparent length of crystallites estimated by other means (6). Frey-T'iyssling (6) and Kratky (8, 10) infused cellulose with gold chloride, reduced the gold, and examined the gold-embedded structure. From the distances between regions containing metallic $old, Kratky calculate4 an average crystallite width of 55 A. and a length of 1000 A. All these investigations indicate directly or indirectly that the primary effect of dilute aqueous solutions is upon the noncrystalline regions of cellulose.
Quantitative data on the hydrolysis of cellulosic materials in boiling 8 per cent hydrochloric acid are presented and discussed. Cellulose probably consists entirely of chains of anhydroglucose units in varying degrees of association, ranging from a dense, crystalline, acid-resistant fraction to an amorphous, easily hydrolyzed fraction. The nonresistant cellulose may comprise less than one tenth of the structure of natural fibers but is considerably higher in derived products. Cotton and wood celluloses appear to differ structurally.
Although water appears to exert only a minor influence on the crystallites, it has considerable effectson the properties of the cellulosic material as a whole, which behasres like an elastic gel ( d L ) . For examnle. the concurrent absorntion of water and swelling in regenerated celluloses cause a notable strength loss. Aqueous swelling in the case of cotton fibers u
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The first paper i n this series appeared In the A n a l y t i o a l E d i t i o n , June
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coincides with a marked decrease in rigidity and TABLE I. DESCRIPTION AND PREPARATION OF CELLULOSIC MATERIALS increase in plasticity ( I , 18). It is evident, Preparation Remarks therefore, that some relation exists between the Material Type amorphous fraction of cellulose and the properties None Linen Fabric Fully bleached Boiled 4 hr. in Unbleached Unmercerized cottona Yarn of the material itself. A summary and discus2y0 NaOH, sion of these relations were prepared by Mark washed (12). Boiled 4 hr. in Mercerized with tenMercerized cotton5 Yarn The available evidence appears to justify the sion 2% NaOH, washed assumptions (a) that the amorphous fraction as Sulfite wood pulp Sheet None Paper stock well as the crystallites of cellulose consist entirely None Rayon grade Purified wood pulp Sheet of anhydroglucose chains, and (b) t h a t the amorWashed in warm Coating removed Cellophane Sheet phous fraction is penetrated readily by water and soapy water Washed in warm Commercial Bemberg Cuprammonium rayon Fabric dilute aqueous solutions. soapy water A method by which the glucose set free during Washed in warm From cotton linters Viscose rayon (I) Cord hydrolysis with dilute acid can be estimated consoapy water tinuously was described in a preceding communiFrom purified wood Filaments None Viscose rayon (11) cation (16). This method has been applied to pulp listed above None Cellulose acetate Flake Acetyl content, 39.4% various common cellulosic materials, including None Water sol.: methoxyl Methylcellulose Flake linen, cotton, mercerized cotton, wood pulps, content, 31'% viscose and cuprammonium rayons, cellulose Pretreated cottons Described in text acetate, and methylcellulose. In addition, a These samples represent the same lot of gray yarn; the mercerized product is the variations in the percentage of hydrolysis a commercial article. The matched pair was boiled and washed simultaneously. of cotton produced by pretreatments with cuprammonium hydroxide reagent, hot 2 Der cent hvdrochloric acid. and cold 40 the nonsubstituted celluloses were kept in vacuo over phosphorus per cent hydiochloric acid hake also been determined. It pentoxide for 24 hours to reduce the moisture content below the should be understood, however, that this study is of a general regain value. Subsequently, the samples were conditioned for nature and that the samples investigated are not necessarily 24 hours at 70" F. and 65 per cent relative humidity, weighed representative of their different classes. accurately, dried thoroughly over phosphorus pentoxide, and reweighed. The previous discussion indicates t h a t hydrolysis would The methoxyl content of methyl cellulose and the acetic acid occur primarily in the amorphous cellulosic network although content of cellulose acetate were determined by the n'iederl (17) a simultaneous b u t slower attack on the higher density mateand modified Eberhardt (13) methods, respectively. rial is probable also. Since water apparently does not penetrate the crystallites in quantity, i t might be expected that the Materials moisture-absorbing capacity of a material would depend The preparation of the cellulosic materials is summarized largely upon the outside surfaces and penetrability of the in Table I. The following specially-treated cotton samples crystallites and upon the surrounding amorphous areas-that were investigated also : is, at the places where hydrolysis could occur. Consequently, measurements of hygroscopicity were made as possible in1. A conditioned 1-gram portion of urified, unmerceriaed direct confirmation of the breakdown of the different subcotton (same as in Table I) was disperse$ in 125 ml. of British stances. Standard cuprammonium hydroxide solution and agitated with glass beads in the absence of air and light for 24 hours. Then the viscous dispersion was stirred into 2 liters of water and neutralMethods ized with acetic acid. The precipitated cellulose was collected on a Buchner funnel and washed successively with cold dilute acetic The amounts of hydrolysis of the different cellulosic mateacid, water, and absolute alcohol. The product was vacuumrials were calculated from carbon dioxide evolution curves. dried at low temperature. Briefly, in the presence of suitable concentrations of ferric 2. An accurately-weighed 0.5-gram sample of the same cotton was immersed in 25 ml. of ice-cold 40 per cent hydrochloric acid chloride and hydrochloric acid, glueose is oxidized rapidly and (20) and stored for 48 hours at 2' C. (A control sample a t room yields carbon dioxide at an approximately linear rate for 6 temperature darkened in about 4 hours. the chilled sample did hours. Under controlled conditions this carbon dioxide not discolor during storage.) The liquid was then removed careevolution rate can be used as a measure of the free glucose in fully with an aspirator, first at low temperature as hydrogen chloride evolved rapidly and later at rising temperatures. The last the system at any instant. The details of the method and sta e of the evaporation was conducted at 60" C. with successive apparatus are discussed elsewhere (16). adcftions of absolute alcohol. The light-brown, highly viscous residue was dried over phosphorus pentoxide and soda-lime at reThe procedure was the same in each case. Approximately 2duced pressure. gram samples of the natural fibers and I-gram samples of the 3. A 5-gram sample of the unmercerized cotton was refluxed regenerated and substituted celluloses were dried in vacuo over overnight in 300 ml. of 2 per cent hydrochloric acid. The prodphosphorus pentoxide. The dry weight of a sample was deteruct, hydrocellulose, was washed thoroughly and dried. mined and the sample placed in the digestion flask with a 150-ml. volume ( raduate cylinder) of stock acid-catalyst solution which containef 2.4 moles of hydrochloric acid and'0.6 mole of ferric Hydrolysis Data chloride per liter. The digestion flask was then attached to the apparatus and the system swept out with carbon-dioxide-free air The carbon dioxide-time data for the various substances induring the 20-30 minutes required to bring the digestion liquid vestigated are presented graphically in Figures 1 and 3. I n to a vigorous boil. Time was reckoned from the onset of boiling. Figure 1the carbon dioxide values for cellulose acetate, cotton The carbon dioxide, collected in Truog columns .containing barhydrolyzed with 40 per cent hydrochloric acid, water-soluble ium hydroxide, was determined periodically by titration with standard hydrochloric acid. Observations were made more fremethylcellulose, and purified cotton are plotted against the quently in the initial stages of the hydrolysis when the most time of digestion. The methylcellulose and cellulose acetate rapid rate changes occur. Titration values were corrected for a data are corrected to 1 gram of substituent-free cellulose. small blank and calculated to a basis of 1gram of pure cellulose. The induction period which precedes the evolution of carbon The method of measuring hygroscopicity was designed t o avoid hysteresis effects (25). Roughly weighed 2-5 gram samples of dioxide was discussed in an earlier publication (16).
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cellulose acetate a t 0.6 hour (1.0 - 0.4). The remainder of the curve may be determined similarly from numerical values of slope found by the analytic method and calculated by the same relationship. Most of the materials investigated yield carbon dioxidetime curves similar to that for cotton (Figure 1). For these the calculation was simplified by the use of an exponential function of corrected time. The equation is K(T)'.'
COz
(2)
where T,the corrected time, is the digestion time, t, in hours minus the induction period, 0.4. Plotted in terms of this equation, the experimental results separate into an essentially linear and a nonlinear group (Figure 3). The materials in the linear group are linen, cotton, and some products derived from cotton cellulose; in the nonlinear, wood pulps and some wood cellulose products. Actually, the latter group of curves is described much better by a modification of the equation used, but for clarity in presentation, this modification was not employed. The broken curves in the lower graph of Figure 3 emphasize the poorness of fit. The conversion of the linear data to percentages of cellulose hydrolyzed, C,, involves the first derivative of Equation 2. The latter represents the instantaneous slope, Sobsvd., which can be substituted in Equation 1. The result is
where K , the velocity constant for the particular material, is FIGURE 1. UNADJUSTED CARBON DIOXIDE-DIGESTION TIME calculated from Figure 3 (upper graph). Numerical values CURVESWHICH REPRESENT 1 GRAMOF SUBSTITUENT-FREE of the percentage of cellulose hydrolyzed can be obtained CELLULOSE IN EACH CASE either graphically or by solving the expression for different values of 2'. The carbon dioxide-time curves, except that for purified cotton, converted to apparent percentages of cellulose hydrolyzed to glucose, are shown in Figure 2 . It is evident that, within a smell error, both prehydrolyzed cotton and the pure cellulose component of the acetate are broken down completely to glucose. The theoretical yield of glucose from anhydroglucoee is 111 per cent, the yield calculated from carbon dioxide data is 110 per cent. The saponification and hydrolysis of the cellulose acetate are almost instantaneous. The acetic acid set free as a result of the saponification evolves no carbon dioxide under the conditions of the experiment. The calculations on methylcellulose may be in error because the methyl groups may prevent oxidation. However, this ether contains about two thirds the maximum possible methoxyl content, and about one third of the cellulose appears to be hydrolyzed to glucose. The method of calculating raw data to percentages of cellulose hydrolyzed was previously described in part (15). Curves of the type shown in Figure 2 can be obtained from the corresponding raw data curves (Figure 1) as follows: ( a ) The carbon dioxide values are replotted against the digestion time, t , corrected for the induction period, 0 . 4 4 . e., t - 0.4. (a) The slope of the straight portion of the curve is drawn and its numerical value, Sobsvd., is calculated. (c) Finally, the slope, S,,., for the same weight of glucose under the same conditions is determined. On the assumption that cellulose consists entirely of anhydroglucose-namely, 111per cent glucose -the percentage of cellulose hydrolyzed, C,, is given by the equation : c h
100
Sobsvd./l.ll
sgl.
(1)
The percentage so calculated represents the flat portion of the corresponding curve in Figure 2 and is attained a t the corrected time ( t - 0.4) of convergence of the true curve and the drawn slope. For example, convergence occurs in the case of
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ACETATE
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FIGURE2. HYDROLYTIC BREAKDOWN CURVES OBTAINED BY C-4LCULATION FROM CARBON DIOXIDE EVOLUTION DATA
The initial linear portions of the curves in Figure 3 (lower graph) can be calculated in the manner just described. The remaining sections respond to the log-log treatment outlined in the previous paper ( 1 5 ) , or the conversion may be accomplished by the inspectional analytic method. The combined errors of measurement and calculation probably do not exceed 5 per cent in any instance. Curves showing calculated percentages of cellulose hydrolyzed with time are presented in Figure 4. The outstanding feature of these curves is the shape; it indicates that, initially, varying amounts of the celluloses are hydrolyzed rapidly to glucose, but that later the residual cellulose becomes more
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rected for its acetyl content both appear to contain 110 per cent of glucose. I n general, the natural and regenerated celluloses examined appear to be composed of two different but ill-defined fractions. One fraction is split out readily by hydrolysis with acid, the other is more resistant. A quantitative differentiation of these fractions is not entirely feasible because the rates of hydrolysis suggest that a progressive increase in resistivity occurs as the digestion proceeds or as the aggregates become smaller. This interpretation is in good agreement with the findings of Staudinger and Sorkin (M), mentioned earlier. If, moreover, the increasing resistivity represents an increasing density and cohesiveness, estimates of micelle length may depend largely upon methods of measurement. The least resistant part of the cellulose structure is probably the amorphous or intercrystalline network. This inference is based on the apparent resistance of the crystallites to acid attack and on the behavior of cellulose acetate which, being a more or less expanded structure, breaks down rapidly. The ester groups of the acetate render the chains incapable of association into impermeable cohesive units. Starch, which is said to be amorphous ( I I ) , breaks down completely in a short time under the conditions (16). More specifically, the curves in Figure 4 indicate the manner in which the relations for the natural celluloses are altered by such treatments as acid hydrolysis, mercerization, dispersion in cuprammonium hydroxide solution, and the viscose process. First, as might be expected, the conversion
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FIGURE3. LINEARGROUP(above) AND NONLINEAR GROUP(below) OF ADJUSTEDCARBON DIOXIDE-DIGESTION TIME CURVESWITH TRB ACTUAL TIMESOF THE OBSERVATIONS INDICATED
and more resistant to breakdown by acid. I n fact, substantial quantities of insoluble material remained in the digestion liquid after each of the runs shown in Figure 4. I n the case of cotton the solid still present after the 7-hour refluxing with acid was filtered off, washed thoroughly, and dried. The powdery white product, probably hydrocellulose, was examined with a microscope and with x-rays. A photomicrograph (Figure 5 ) of this substance revealed that it consists entirely of broken cotton fibers. X-ray diagrams (Figure 6) of this material and of a mat of unhydrolyzed cotton are identical and demonstrate that, under the conditions employed, hydrolysis does not alter the crystallite pattern appreciably. The more or less linear relation of velocity constants to moisture regain can be seen in Figure 7. Velocity constant K of the carbon dioxide reaction is directly proportional t o the velocity constant of hydrolysis.
Composition of Cellulosic Materials The present evidence offers further support for the generally accepted idea that pure cellulose is composed entirely of anhydroglucose. Purified cotton hydrolyzed completely with 40 per cent hydrochloric acid and cellulose acetate cor-
V I S C O S E R A Y O N (Wood
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FIGURE 4. HYDROLYTIC BREAKDOWN CURVESFOR NATURAL AND REGENERATED CELLULOSIC MATERIALS OBTAINED BY CALCULATION FROY CARBON DIOXIDE EVOLUTION DATA
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The relation in Figure 7 between moisture regain and velocity constant, K , appears to be valid over a considerable range. It can be shown that K is proportional to the rate of hydrolysis of a material. I n general, therefore, the moistureabsorbing capacity for a nonsubstituted cellulose seems to be a measure of the rate a t which hydrolysis can occur. It is probable that such properties as plasticity, extensibility, and even strength of cellulosic materials are dependent upon the least resistant, amorphous, or expanded fraction, but the establishment of a quantitative relation is not simple. First, if, as the curves in Figure 4 indicate, the least dense and resistant areas in the material shade into the most dense,
ON COTTON FIBERS FIGURE 5. EFFECTOF ACID HYDROLYSIS
( X 360)
-of cotton to hydrocellulose resulted in aloss in available glucose. Secondly, mercerization of cotton increased the availability of glucose or, conversely, decreased the amount of resistant cellulose. Thirdly, dispers'on of the cotton in cuprammonia solution reduced the quantity of resistant cellulose appreciably. The preparation was recovered from a dilute solution, yet it contained a higher percentage of resistant material than did the stretch-spun viscose rayon from cotton linters. It is possible that the cuprammonia reagent did not effect an equivalent dissociation. A comparison of the wood and cotton cellulose curves is suggestive. Wood cellulose appears to contain B higher proportion of easily hydrolyzed material than cotton cellulose
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FIGURE 7. RELATION OF MOISTURE REGAINOF NATURAL AND REGENERATED CELLULOSE TO VELOCITY CONSTANTS OF HYDROLYSIS
crystalline areas, it is conceivable that amorphous regions of intermediate density exist where forces of interaction between chains could produce rigidity. I n other words, from the point of view of properties some of the amorphous fraction may behave like the crystalline component. Secondly, the present measurements were made in an aqueous medium while the functional properties are most often those of the conditioned materials. However, there may be a proportionality between the wet and dry properties. Finally, the hydrolysis-time curves undoubtedly represent the combined simultaneous breakdown of both amorphous and crystalline fractions. It is suggested from a consideration of these factors that the effective amount of amorphous cellulose in a sample does not exceed the percentage available in half a n hour under the conditions. These studies are being extended to include viscosity phenomena and to clarify some of the points discussed.
Literature Cited
FIGURE 6. X - R A Y DIAGR.4MS O F ACID-HYDROLYZED COTTON(above) AND A MAT OF UNHYDROLYZED COTTON(below)
and possibly a more resistant residual fraction. The same relation appears to obtain in the processed celluloses. This difference between cotton and wood celluloses may be structural and may account for some of the differential behavior of these materials in practice.
Brown, K. C., Mann, J. C., and Peirce, F. T., J . Textile Inst., 21, T188 (1930). Conrad, C. M., and Berkley, E. E., Textile Research, 8, 341 (1938). Farr, W. K., Contrib. Boyce Thompson Inst., 10, 71 (1938). Farr, W. K., J . P h y s . Chem., 42, 1113 (1938). Frey-Wyssling, A., Protoplasma, 27, 569 (1937). Hengstenberg, J., and Mark, H., Z.Krist., 69, 271 (1928). Kats, J. R., Physik. Z.,25, 321 (1924). Kratky, O., S i l k and R a y o n , 13,480,571, 834 (1939). Kratky, O., and Mark, H., 2. physik. Chem., B36, 129 (1937). Kratky, O., and Schoszberger, F., Ibid., B39. 145 (1938). Mark, H., Chem. Rev., 26, 169 (1940). Mark, H., d . P h y s . Chem., 44, 784 (1940). Murray, T. F., Jr., Staud, C. J., and Gray, H. LeB., IND.ENG. CHEM., Anal. Ed., 3, 269 (1931).
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(14) Nickerson, R. F., IND. ENQ.CHEM.,32, 1454 (1940). (15j Nickerson, R. F., IND. ENQ. CHEM.,Anal. Ed., 13,423 (1941). (16) Nickerson, R. F., and Leape, C. B., IND.ENG. CHEM.,33, 83 11941). ~ ----
(17) Nieder1,’J. B., and Niederl, V., “Micromethods of Quantitative Organic Elementary Analysis”, p. 192, New York, John Wiley & Sons, 1938. (18) Peirce, F. T., ShirleyInst. Mem., 3,253 (1924). (19) Reeves, R. E., and Thompson, H. J., Contrib. Boyce Thompson Znst., 11, 55 (1939). (20) Sherrard, E. C., and Froehlke, A. W., J . Am. Chem. SOC.,45, 1729 (1923). (21) Sisson, W. A., Contrib. Boyce Thompson Inst., 8 , 389 (1937).
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(22) Sookne, A. M., and Harris, M., J . Research Natl. Bur. Standurds, 25, 47 (1940). (23) Staudinger, H., and Sorkin, M., Ber., 70, 1565 (1937). (24) Urauhart. A. R.. J. Teztile Inst.. 20. T125 (1929). (25j Urquhart, A. R., and Williams, A. M., Ibid., 14, T390 (1923). (26) Whistler, R. L., Martin, A. R., and Harris, M., Am. Dyestuf Reptr., 29, 244 (1940). (27) Whistler, R. L., Martin, A. R., and Harris, M., J . Research Nu& Bur. Standards, 24, 13 (1940). CONTRIBUTION from the C o t t o n Researoh F o u n d a t i o n Fellowship. Mellon Institute.
Bulk Fermentation Process for Sparkling Cider D. IC. TRESSLER AND R. F. CELMER New York State Agricultural Experiment Station, Geneva, N. Y.
E. A. BEAVENS Bureau of Agricultural Chemistry and Engineering, U. S. Department of Agriculture, Geneva, N. Y.
N ALL apple-producing regions of the world, fermented
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apple juice (cider) has been a popular beverage for centuries. I n France, Germany, and England sparkling cider, made by a secondary fermentation of cider in bottles (champagne process) or in bulk by a closed tank (cuv6e) process, is produced on an extensive commercial basis. The use of the bulk or closed tank method for the manufacture of sparkling cider possesses many advantages over the laborious in-the-bottle procedure. It is much more rapid, requiring only 5-7 days as compared to 3-6 months by the inthe-bottle method, and much less labor is needed t o clear the cider by filtration in bulk than by the old-fashioned disgorging process. Two costly corks are required for champagne bottles, while the sparkling cider may be filled automatically into
Semicommercial scale experiments on the production of sparkling cider by the secondary fermentation of cider in glass-lined pressure tanks indicate that the speed of carbon dioxide formation can be accelerated greatly by the addition of either apple juice or a concentrate prepared therefrom and a small amount of ammonium monohydrogen phosphate to the cider. Fermentations proceed more rapidly a t 70’ F. than a t either a slightly higher or a slightly lower temperature. The choice of the strain of wine yeast is of great importance in determining the rapidity of carbon dioxide production.
bottles and closed with crowns. Much lighter and consequently less expensive bottles are required when the fermentation is carried out in tanks. Armstrong (3) stated that the secondary fermentation in bulk by a closed tank process was originally developed in France by Maumene many years ago and has been furthered by several workers here and abroad. The first patent in this country on a similar process was granted to Garrett in 1902. Tschenn (8, 9) described the process for sparkling wines and ciders which was first introduced in France by Eugene Charmat in 1910, involving use of metal tanks of 1000-gallons capacity capable of withstanding 200 pounds pressure. Rougier (7) also described the Charmat process. Alwood ( 1 ) reported on cider making in France, Germany, and England. I n 1904 Alwood and others (a) published results of experimental cider making in this country in which sparkling cider was made by secondary fermentation in the bottle. Modern technology of cider making in France, including the closed tank process, was reviewed by Warcollier (10). The traditional champagne process of secondary fermentation in the bottle which requires much skill and labor was best de-
If the yeast food and supplements suggested are added to cider inoculated with a rapidly fermenting starter of the proper strain of champagne yeast, secondary fermentation occurs rapidly, 90 pounds per square inch carbon dioxide pressure developing in 3-4 days. Chilling and bottling require another 24-36 hours. Thus the entire process of converting cider to sparkling cider requires only about 5 days. The flavor of the product is improved by the addition of tannin to thecider before fermentation and of a small amount of invert sugar and apple brandy a t the time of bottling.
