FAST CONVERSION OF DISTILLERY MASH FOR USE IN A CONTINUOUS PROCESS F. H. GALLAGHER, H. R. BILFORD, W. H. STARK, AND PAUL J. KOLACHOV Joseph E. Seagram & Sons, Inc., Louisville, Ky.
Over 70 per cent of cooked grain starch is converted to maltose (as determined by standard methods) by the action of barley malt in one minute at 62.8' C. Alcohol yields obtained by the fermentation of mashes converted for one minute at 62.8O C. are approximately 2 per cent higher than
those obtained with the standard practice of 30-60 minutes at 62.8' C. The physical properties of mash converted for one minute are such that the process is readily adaptable to plant practice on a continuous basis. The process operates successfully on a production basis.
HE distilling industry has been one of the most backremoved a t 5-minute intervals up to 60 minutes for maltose and total sugar analysis. The results were calculated as ward from a technical viewpoint. Only minor refinements have been made in processing methods for the grams glucose per 100 cc. Per cent conversion represents reducing' substances calculated as maltose over total sugar last several years, with the exception of distillation. Our laboratories have concentrated on the modernization of the as glucose. Results are graphed in Figure 1. These data indicate a rather surprising amount of convermethods involved in grain processing-cooking, conversion, yeast production, and fermentation. The objective toward sion after the relatively short time of 5 minutes. The ordiwhich this work is directed is to reduce the processing time nary iodine conversion test indicated very poor conversion a t from 80 to 5-10 hours, to eliminate batch processing, and to this point. The conversion figures from the 30-minute peemploy a continuous system which is more readily controlled, riod on are normal for the batch procees. simpler in design, and easier to operate. I n addition, the amount of material and cost of construction would be reduced greatly. The work reported here is concerned only with the studies on grain conversion. Formerly grains such as corn were cooked in a large batch, cooled to 62.8-65.5" C., a barley malt slurry was added, and the entire batch was held a t the conversion temperature for 30-60 minutes. This single batch was then pumped through coolers and into the fermenters. This cycle requires a large mash vessel and a cycle of 1 to 2 hours, depending on the equipment. I n order to make this operation a continuous process without resorting to an unwieldy apparatus, it was essential that the conversion time be reduced to a period of not over 5 minutes. In other words, a pipe line processwas desired. T H E first experiment was designed to determine the percentage conversion obtained in a grain mash held a t 62.8" C. for different periods of time. A corn cook was prepared and cooled to 62.8" C., and barley malt slurried in water was added t o the rapidly agitated cook. The ratio of grain was 90 per INTHE OLD METHOD,MALTWASADDEDTO THE MASHIN THE TUB;MALT cent corn, 10 per cent malt. Samples were AND MASHWERE HELDHEREFOR 45 TO 60 MINUTES AT 62.8" C .
T
1395
1396
OF EFFECT OF MASHCONVERSION TIMES TABLIE I. COMPARISON ON FERMENTATION YIELDS
Copver-
mon Time Min.'
Vol. 34, No. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
Initial g./lOO Gc.
Total Sugar Efficiency, % Fermen- Plant Final Ferbasis g./100 bo. mented, % tation
Grams Abs. Alcohol/ 100 Cc.
1
11.61
0.627 0.629 0.630
94.5 94.5 94.5
98.4 99.1 98.4
93.1 93.8 93.1
5.52 5.56 5.62
5
11.58
0.616 0.672 0.685
94.6 94.2 94.0
99.3 99.4 100.7
93.9 93.8 94.8
5.56 5.55 5.61
15
11.54
0.745 0.715 0.752
93.5 93.8 93.8
100.2 101.1 100.0
93.5 94.7 93.4
5.52 5.59 5.51
30
11.28
0.810 0.856 0.792
92.8 92.4 93.1
99.3 102.5 95.0
92.2 94.8 88.5
5.31 5.46 5.10
45
11.87
0.856
92.8 92.5
98.0 89.1
90.9 82.3
5.52 5.00
0.885
All fermenters were inoculated from the same flask of yeast and incubated for the same length of time under the same conditions. Final analyses were run after 68-72 hours of fermentation. Sugar analyses were made by the method of Stiles, Peterson, and Fred1, and alcohols were determined on distilled samples with the Zeiss immersion refractometer. Efficiency data were calculated on the basis of one molecule of glucose producing two molecules of ethyl alcohol. Thus, the theoretical yield is 0.511 gram of alcohol per gram of glucose. Fermentation efficiency is actual yield divided by theoretical, as calculated from sugar fermented times 100. Plant basis efficiency is actual divided by theoretical, as calculated from total initial sugar times 100. The latter method is in use for the evaluation of plant operating efficiency. The former analysis of data yields information on the validity of the data and the effect of experimental conditions on the yeast.
ANALYSIS of the data in Table I reveals the following facts: Conversion times of 1, 5, and 15 minutes result in somewhat pH A N D TIYEAS FACTORS INFLUENCING TABLE11. CONVERSION higher alcohol yields than longer conversion times. In addiFERMENTATIOX YIELDS tion, there is a greater degree of consistency between indiGrams Total Sugar E5ciency, % Abs. AIvidual fermenters. Reducing the data to plant efficiency, the Time Initial Final Fermented, Fermen- Plant cohol/ same picture holds, and this is important because any slight hlin.' g./100c'c. g./100 Lc. % tation basis 100 Cc. PH variations in mash concentrations are eliminated by initial A . Preliminary Experiments sugar analyses. The fermentation efficiency data are normal 90.5 6.02 13.01 0.734 94.2 96.1 5.45 60 0.730 94.1 97.6 91.8 6.11 and good for 1-minute and most 5-minute conversions. It is 90.5 6.02 0.739 94.1 96.2 slightly high for the 15- and 30-minute periods, probably due 95.2 6.26 12.90 0.652 94.9 99.7 1 to slight error in sugar analyses. With the exception of the 95.4 6.29 0.638 95.0 99.9 last fermenter, i t is normal for the 45-minute period. This 95.3 6.28 0.677 94.8 100.1 case may be due to an error in alcohol analysis, so the data on 90.2 5.93 12.86 0.838 93.6 96.3 5.85 60 0.823 93.8 98.9 92.7 6.09 that fermenter might be disregarded. Of considerable impor... .. .. 0.801 93.9 tance is the per cent sugar utilization. This is in inverse ratio 94.8 6.11 1 12.60 0.684 94.6 100.1 to the length of time the mashes were converted. Final sugar 0.653 94.8 100.4 95.8 6.18 data indicate better carbohydrate utilization with short time 96.5 6.24 0.648 94.8 101.0 conversion. This is very significant. B . Check Experiments 5.50
6.90
60
12.80
0.814 0.803 0.783
93.5 93.9 94.0
96.2 96.5 95.5
90.0 90.4 90.0
5.89 5.93 5.88
1
12.61
0.635 0.646 0.644
94.8 94.7 94.8
98.9 98.0 98.8
93.8 93.0 93.6
6.06 5.99 6.04
60
13.05
0.898 0.938 0,918
93.2 92.9 93.0
94.7 96.5 97.1
88.4 89 8 90.4
6.87 5.98 6.02
1
13.02
0.684 0.654 0.673
94.6 94.8 94.7
98.3 96.4 97.5
93.1 90.9 92.3
6.20 6.05 6.14
Although the per cent conversion after 5 minutes a t 62.8' C. was below the normal figure, and the iodine test indicated a preponderance of starch and high-molecular-weight dextrins, it was decided to determine the fermentation efficiency and yields on mashes convgrted for short periods. Since even with the old type of conversion some conversion of dextrins occurs during fermentation, it was believed that the same would be true of only partially converted mashes. Corn cooks were prepared in the laboratory under identical conditions and were cooled to the conversion temperature of 62.8" C. To each cook was added the same amount of barley malt as a slurry. The cook was mechanically agitated during mashing. The conversion times were 1, 5, 15, 30, and 45 minutes. At the end of the conversion period the mash was cooled as rapidly as possible to the initial fermentation temperature of 22.2' C. This required 7 to 10 minutes. The mash was then made up to the final volume of 38 gallons mash per bushel of grain, and the p H adjusted to 4.8-5.0. Each mash was then divided into four portions. Three were inoculated with the Seagram S o . 1strain of Saccharomyces cerevisiae, and the fourth portion was saved for analysis,
100
1
I
I
5
FIGURE1.
IO
I
15
20 25 30 35 CONVERSION TIME
RELATION
I
I
I
40
45
50
55
60
(MIN.)
TIME AND PER CENT STARCH CONVERSION OF
Starch, cooked corn mash; conversion agent, barley malt; temp., 62.8' C.
When additional tests had confirmed the facts reported in Table I, it was believed important to compare the 1-minute with a 60-minute conversion period under different pH conditions. I n plant practice it is desirable to convert a t pH levels between 5.4 and 5.9. Although this is a relatively narrow range, the results were checked. These experiments were run and analyzed as described above, and the results appear in Table 11.4. 1 Stiles, H. R., Peterson, W. H., and Fred, E. B., J. Bact., 12, 428-35 (1926).
November, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
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4. The high rate of action permits use of a simple conversion unit.
There are difficulties involved in applying this process to the standard batch cooking process. However, simultaneously with this development, our laboratories had worked out a continuous cooking system so that a steady stream of cooked grain was available for continuous, rapid conversion. Both processes have been installed in one of the plants; the cooking operation has been in for one year, the conversion process, for about three months. The conversion equipment is nothing more than a small proportioning pump which continuously injects a malt slurry into the stream of cooked grain just ahead of the mash pump, then a section of 4-inch pipe 105 feet long, txrough which the mash passes. This unit has sufficient capacity to convert 5000 bushels of grain a day. The standard practice would involve tanks with a total capacity of 11.000 gallons, equipped with mechanical agitators. The discharge from I N ~ T HNEW E METHOD,MALTIs METERED OUT THROUGH THE PUMP AND the pipe section is directed into the mash MIXEDWITH THE MASHIN A PIPE L I N APPROXIMATELY ~ 105 FEETLONG; coolers. With the present mashing capacity TEIB MALTIs IN CONTACT WITH THE MASH FOR 40 SECONDS AT 62.8" C. PRIOR TO COOLING. of the plant in question, this means that any given unit of grain is converted for 40 seconds a t 62.8' C., and is then passed into coolers and cooled to 21.1-23.9' C.in 1.5 minutes. The plant efficiency data show that the 1-minute converPlant yields obtained with this process are presented in sion time is equal to or superior to the 60-minute period a t Table 111. These data are from the actual full-scale, 5000either pH level. The differenceseems to be slightly greater at bushel-a-day plant, operating on a definite predetermined a pH of 5.45. Again, final sugars are lower in the case of the schedule. These yields for the two-week average are very short conversion time and the per cent sugar fermented is good, and are for the second and third week of operation with slightly higher. this unit. The following period of two weeks indicated even Table IIB indicates data from a check experiment on pH higher yields. We realize that i t is difficult to evaluate a and time; the same trends are shown. All of these data inprocess on two-week production data because of variations in dicate a slight superiority in favor of the 1-minute or flash constarch content of grain and other factors. However, effiversion process as compared with the customary conversion ciency data for the operations to date have been high, 92process. This is one point greatly in favor of this process, 93 per cent. Furthermore, the yields reported in Table I11 since it represents an increase in yield equivalent to about 2 compare favorably with the best periods using the standard per cent, or 0.1 proof gallon per bushel of grain mashed. This conversion practice. is of great importance when 5 to 10 thousand bushels may be mashed daily in a single plant. At present no data are available that will yield any light on the reason for apparent increases in yield. However, it is TABLE 111. PLANT YIELDSOF ALCOHOLOBTAINED WITH CONbelieved that one of two factors, or both, may be responsible. TINUOUSLY CONVERTED MASH,IN PROOF GALLONS PER BUSHEL First, due to the brief holding period, there is little destruc(14-day test period, 40-second conversion eriod; 42 fermenters of 44,000 tion of the amylase system during conversion, although an gallons each? unexpectedly high degree of conversion occurs. Thus, the Analytiaal Actual Anslytiad Actual balance of the amylase is available for use in the fermenter. 5.33 5.19 6.25 5.28 5.53 6.42 5.27 6.23 With the long holding period, the equilibrium point is reached 6.26 5.14 6.07 5.02 and the amylase is destroyed by the higher temperature with 5.04 6.02 5.08 5.13 6.48 5 . 3 6 5 . 2 9 5.32 no advantage gained. This factor is substantiated by the 6.31 6.31 5.23 6.05 5.24 5.13 Av for consistently lower final sugars formed with the fermentation of 5.57 6.44 period 5.28 5.22 flash-converted mashes. The second factor is the possibility of a reduction in concentration of certain heat-labile factors in malt that are necessary for maximum fermentation efficiency. As mentioned before, a combination of factors may be reIt should be stated that Joseph E. Seagram & Sons, Inc., sponsible. has the only unit in production. However, due to the emergency conversion of industrial alcohol plants from molasses SEVERAL facts favored the practical application of this into grain, many other concerns are adopting this process. formation: Obvious reasons are the small amount of material required, 1. Alcohol yield is equal to or superior to the standard prothe ease and rapidity of fabrication, and the low cost. The cedure. process has been operated on corn, wheat, and rye, with either 2. The mash is sufficiently fluid for handling with standard barley or rye malt. and coolers. I mash 3. Su cient conversion occurs instantaneously to permit immediate inception of yeast growth and fermentation in the P~RWHINTED before the Division of Agricultural and Food Chemistry at the 103rd Meeting of the AMHIRICAN CHBMICAL SOCIBITY, Memphis, Tenn. fermenter.
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