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provided from standard stock equipment. The condenser and automatic refrigerating equipment are operated at a temperature only slightly above 0" C., and temperatures are automatically controlled.
tion valences satisfied is zero a t all temperatures less than 130" C. The final stage of the dehydration to form anhydrous magnesium perchlorate (Anhydrone) is carried out at temperatures between 200" and 250" C. The equipment described has a capacity of 100 pounds of the finished product, Operation of Dehydration Equipment and such a charge requires approximately 20 hours of continuThe practical operation of the dehydration equipment de- ous evacuation and the liberation of between 40 and 50 pounds scribed was tested, using as the reaction the dehydration of of water as condensate. The known tendency of this product magnesium perchlorate hexahydrate to form anhydrous to fuse during dehydration under conditions other than that of magnesium perchlorate. The successive steps in the dehydra- uniform heat distribution attest to the efficiency of the aption of this product to form the super-drying reagent sold paratus described in overcoming this troublesome factor. For this dehydration a favorable working pressure is 5 mm. under the trade name of Anhydrone are the following, which of mercury. Pressures in excess of this value are prohibitive will be described in a subsequent paper: for the manufacture of Anhydrone, since the temperature Mg(OHi)a(ClO4)r = Mg(OH*h(C104)2 = Mg( OH&( C10& = Mg( C104)1(Anhydrous) cannot be increased to a value greater than 250" C. because of decomposition. At this temperature the vapor pressure is The vapor pressure of the hydrated magnesium perchlorate thought to be approximately 10 mm. of mercury. The use of with four of the coordination valences of magnesium satisfied the equipment described for large-scale generation and reis zero a t temperatures less than 50" C. The vapor pressure generation of Anhydrone for use in the commercial drying of of the perchlorate with but two of its normal of six coordina- gases to produce a bone-dry product is suggested.
Elimination of Thermophilic Bacteria from Sugar' E. J . Cameron and W. D. Bigelow RESEARCH LABORATORIES, NATIONAL CANNERS ASSOCIATION, WASHINGTON, D. C.
Three major groups of thermophilic spore-bearing HERMOPHILIC spoilhas been stressed in various bacteria, in the main dissimilar but possessing in compublications. When the sigage in c a n n e d prodmon the properties of high-temperature growth and nificance of the relation beucts of low acidity has ability to produce spores of high resistance to heat, are tween thermophilic bacteria been a c o n t i n u i n g cause of of major importance as causes of spoilage in nonand spoilage in canned foods economic loss to the canning acid canned vegetables. In work done since 1926, it was r e a l i z e d , there was an industry. Studies of causes has been established that refined sugar may be cona w a k e n i n g of both specific of this type of spoilage have taminated with one or more of these major groups, and g e n e r a l interest in this disclosed that three major and, under such circumstances, be a direct or indirect group of bacteria. Morrison groups of thermophilic sporecause of spoilage. Tentative Bacterial Standards for and Tanner (14,15) have prebearing b a c t e r i a a r e conSugar for the Year 1931 have been announced by the sented a comprehensive rec e r n e d . These groups are Research Laboratories of the National Canners Asview of the literature relating distinctly dissimilar with resociation. At the present time at least nine organizato thermophilic bacteria and spect to various physiological tions engaged in the production of refined sugar have have contributed general incharacteristics, but they posstated that they are prepared to furnish sugar which f o r m a t i on regarding their sess in common the properties meets the standards. systematic relationships. of high-temperature growth T h e c o n t r i b u t i o n s of and ahlity to producespores of high resistance to heat. The latter property is obviously Barlow ( I ) , Weinzirl (19), Cheyney (8), Bigelow and Esty (2), James (la), the predominant reason for their importance to the canning in- Esty and Stevenson (IO), Cameron and Esty (I), Werkman and Weaver ( $ I ) , and Werkman (20) have had dustry. The three groups are briefly described as follows: flat specific reference to thermophilic bacteria in canning. These sour bacteria, which cause non-gaseous acid fermentation; writers have given especial attention to consideration of classithermophilic anaerobes, characterized by the production of fication, heat resistance of spores, distribution, and spoilage acid and gas, the gas being composed principally of hydrogen manifestations. and carbon dioxide in varying proportions; and thermophilic Distribution of Thermophilic Spoilage Bacteria anaerobes, characterized by production of gas, of which The distribution of thermophilic spoilage bacteria and their hydrogen sulfide is the principal constituent, without apprecisources with reference to canning operations have been the able production of acid. Barlow (1) in 1913 demonstrated some of the fundamental subjects of much speculation and study. Until 1926 the cauRes of thermophilic spoilage. The data which he pre- weight of opinion undoubtedly was that presence or absence sented were also valuable in indicating something of the impor- of thermophilic spoilage bacteria was associated with the tance of this type of spoilage. Previous to Barlow's work, there method of handling the raw product. It was logical to assume are indications in the literature that the role of thermophilic soil to be the primary source of these organisms and, indeed, bacteria in spoilage was suspected, but supporting data were tests showed that various types of thermophilic spore-forming bacteria were widely distributed in soil. These tests were lacking. The importance of thermophilic spoilage in canned foods for thermophilic spore formers generally and not for the socalled spoilage types. Developing the basic idea further, it Presented before the Division of 1 Received September 21, 1931. was conceived that the raw product would heat on holding and Sugar Chemistry at the 82nd Meeting of the American Chemical Society. that because of the rise in temperature there would be a Buffalo, N. Y.,August 31 to September 4, 1931.
T
December, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY
significant development of thermophilic bacteria, to which could be attached the blame for subsequent spoilage. Theories of this order have not been substantiated. Barlow (1) performed certain experiments, the results of which indicated that thermophilic spoilage in corn did not result from holding the raw product. His findings and resultant conclusions in this connection were either unknown or disregarded up to 1926, a t which time they were cclnfirmed by Cameron, M'illiams, and Thompson (6),who reported on a series of studies of causes of thermophilic spoilage and concluded that, when thermophilic spoilage occurs, it is due to contamination within the cannery or to contamination conveyed by something other than the basic raw product. Thermophilic contamination was found in such articles of equipment as wood tanks used in preparation of brine or for storage of hot water. Blanching, preheating, and filling equipment were also found to be capable of harboring contamination. With respect to the initial source of contamination, it was found that spores of spoilage thermophiles could be found to a limited extent in soil, while refined sugar was found to carry similar contamination with greater frequency and generally to a much greater extent. Following these and similar studies, granulated sugar has come to be regarded as an outstanding source of thermophilic contamination. Sugar as Source of Thermophilic Bacteria
A general survey of the sugar situation was made with the idea of determining whether granulated sugar from any source is invariably free from thermophilic spoilage bacteria, and whether sugar from any source or by any method of manufacture is invariably so contaminated as to be unfit for canners' use. The results of this study were reported by Cameron and Williams ( 5 ) . The survey comprised tests on a large number of samples which included: refined cane sugar; raw cane sugar; miscellaneous forms of cane sugar, such as soft sugar; white beet sugar; and beet sugar in other forms, such as raw or brown sugar. The "flat sour" group was the one most frequently encountered. Flat sour spores were found in essentially all of the cane-sugar samples that were examined. There was wide variation as regards number of spores in the individual samples. Both types of thermophilic anaerobes were found in many samples and sometimes in undesirable numbers. The general statement may be made that the flat sour bacteria were found in refined cane sugar to a greater extent than in white beet sugar, but the white beet sugar was a t times found to be quite as undesirably contaminated with spores of thermophilic anaerobes. K'either the refined cane nor the white beet sugar possessed any consistent advantage. I n both classes samples of low contamination and also of undesirably high contamination were found. James ( I S ) confirmed the findings of Cameron and Williams with respect to the existence of thermophilic spoilage bacteria in raw and commercial sugars. He reported the isolation of spoilage thermophiles from sugar of all types examined. Following the preliminary general survey of the sugar situation, the sugar used in canning low-acid vegetables has been closely checked by means of tests on samples collected from and submitted by various canners. The information compiled for 1928 and 1929 has been reported by Cameron (3). Significance of Sugar Contamination in Canning
While granulated sugar may be so highly contaminated or carry contamination of such high resistance as to be a direct cause of spoilage, it is felt that under most circumstances the role of contaminated sugar as a medium to inoculate e q u i p ment, such as brine tanks and preheaters, is of greatest signifi-
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cance. At these points, when conditions for bacterial growth and sporulation are favorable, the contamination carried by the sugar may develop to substantial proportions and lead to spoilage. Where the sugar flora is primarily made up of the so-called "obligate" thermophiles, which will not grow in canned corn or peas below a temperature of 38" C. (100" F.),spoilage would result only if the canned product were undercooled after processing, or if shipped to a torrid climate; but the primary fault would rest with the sugar contamination. The attainment of total sterility in non-acid products is a worthy objective, and, because it would be impracticable to process to a degree necessary to destroy the most resistant obligate thermophiles, it is necessary that such organisms be prevented from gaining admission to the product during the canning. In a report by Cameron and Yesair ( 7 ) ,details were given of an experiment in canning which had been made to demonstrate the direct effect of contaminated granulated sugar in causing spoilage. Corn known to be free from spoilage thermophiles was canned in three lots. The first contained no sugar, the second contained a sugar considered suitable for canning, and the third contained an unsuitable sugar. The sugar considered suitable for canning had a flat sour count of 60 spores per 10 grams of sugar. The non-suitable sugar had a flat sour count of about 2500 spores per 10 grams of sugar. The Tentative Bacterial Standards (referred to later) specify a maximum limit of 75 flat sour spores per 10 grams of sugar. The processes given the control corn, which had no sugar, and the suitable and non-suitable sugar were 70, 80, and 90 minutes a t 121' C. (250' F.). The 70-minute process is that recommended for processing corn in No. 2 cans (17) and is about the limit to which this product may be processed without appreciably lowering its quality. Table I presents the general results of this experiment. Table I-Spoilage in No. 2 Cans of Corn Due to Presence of Thermophilic Bacteria in Sugar PROCESS AT 1 2 1 O C. SPOILAGE I N CORNWITH: (250' F.) N o sugar Sugar A" Sugar Bb Minufes % % % 70 0 0 95.8 80 90
a
0 0
0 0
75 54.2
Suitable for canning non-acid products: flat sour count, 60 spores per
10 grams of sugar.
for canning non-acid products; flat sour count, 2500 spores per 10 grams of sugar. b Non-suitable
The bacteria in the suitable sugar were destroyed by the 70minute process, whereas 95 per cent of the cans containing the unsuitable sugar were not sterilized. Furthermore, 90 minutes a t 121" C. (250" F.), which is an entirely impracticable process, was not sufficient to produce sterility in the corn which contained the unsuitaMe sugar. If a canner using this sugar had uncontaminated equipment, he would, nevertheless, be marketing a non-sterile product by reason of the sugar contamination. If, during the height of the corn pack, cans were not cooled to about 38" C. (100" F.), or if the product were shipped to the tropics, it is not unlikely that spoilage would occur. Collaboration between Sugar and Canning Industry The activity of the sugar industry in making practical application of the results of these studies has been very gratifying. Since the earliest information on the subject was made available, a growing interest on the part of the sugar industry has been apparent. The cooperation between the two branches of the food industry has received editorial comment (11). The National Canners Association announced Tentative Bacterial Standards for Sugar for the Year 1931 (16). The standards were formulated partly a t the instance of agencies in the sugar industry and partly because it was appreciated that
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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it would be desirable to issue notice of the values upon which the Research Laboratory of the National Canners Association would base its opinion where such an opinion was requested by its membership. There have been collaborative studies in two sugar refineries. Suggestions have been made with reference to methods and interpretation of results. Laboratory workers have been trained to conduct control work. The result has been that, a t least nine organizations engaged in the production of refined sugar have stated that they are prepared to furnish sugar which meets the 1931 standards. A great many samples of “guaranteed” sugar shipped to canners have been tested, and all have complied with the standards mentioned above. In some instances, sugar practically free from contamination is being produced at refineries which formerly marketed a product repeatedly characterized as being unfit for canners’ use. The effect of these sugar studies will possibly reach beyond their specific application to the canning industry, although the resistant thermophiles with which that industry is concerned are, so far as is known a t present, not of proved industrial importance elsewhere. While experimental proof is lacking, it is logical to suspect that these spoilage bacteria may be found to be of importance to the refining industry directly. Owen (18) has shown that some of the spore-forming bacteria suspected of playing a part in the deterioration of raw sugar were capable of growth a t elevated temperatures. His descriptions do not correspond with any of the spoilage thermophiles discussed here, but it is known that the latter are present in raw sugar, and there is a possibility that they may be involved. It has been found in this laboratory2 that the flat sour thermophiles can grow in as high as 40 per cent raw sugar sirup. Growth of the bacteria and acid production are rapid in concentrations up to 25 per cent. This acid production and neutralization of the acid represent loss of sugar, and such growth could well take place in sweet water or elsewhere where the concentration is within the zone of growth. Contamination in the Rednery
Early study ( 5 ) indicated that there n a y be various phases of contamination within the refinery. In the particular operation which was studied, it was found that raw sugar carried a mixed-spore contamination into the refinery. After filtration there was a condition approaching sterility, at least with respect to thermophilic spores. In the operations subsequent to filtration, there was an increase of flat sour contamination and the final sugar contamination was greater than that in the raw sugar being used at the time. With the data derived from this study, it was possible to demonstrate the effect of concentration in increasing the number of spores per unit volume of sirup. Tests made during successive crystallizations of sugar showed material increase of contamination in the mother liquor. This effect was so marked that it could not be discerned whether or not there was an increase from actual growth. While general deductions could not be made from the data obtained in this first refinery study, i t appeared that filtration and crystallization were the predominant elements of the operation effecting reduction in contamination: the first by actual removal of the spores, and the second by exclusion from the crystals. These two effects were studied in a second refinery where experimental equipment was used but prevailing practice f o t lowed as closely as possible. I n order to observe more clearly the results of the treatment, the original sirups were inoculated with relatively large numbers of flat sour thermophiles. 9
Unpublished data.
Vol. 23, No. 12
The first experiments were designed to test the effect of crystallization. The original contamination of the sirup was 70,000 spores per cubic centimeter. The final sugar, when brought back as a sirup to the original concentration, had a contamination of 11,000 spores per cubic centimeter. If this reduction were to be accepted as representative, i t would be about 85 per cent. Certain inconsistencies in experimental data, however, forbid the use of strictly quantitative expression, and the most that may be said is that a material reduction was effected by crystallization. Further than that, it is obvious that with a sirup of original high contamination the single expedient of crystallization is not sufficient to produce a low-count sugar. Filtration experiments gave results of similar character. One hundred gallons (189.5 liters) of sirup, inoculated with flat sour thermophiles to a concentration of 25,000 spores per cubic centimeter were run through an experimental filter. Five pounds (2.3 kg.) of the filtering material were mixed with the contaminated sirup just previous to filtration. This was a somewhat higher amount of filtering material than is used commercially, but it was necessary because of the small size and the construction of the filter. The sirup was pumped from a drum through the filter and back to a second drum. Then the operation was reversed and the sirup was put back through the filter and into the original drum. All told, the sirup was put through the filter four times. Following the four successive filtrations, approximately 30 gallons (113.7 liters) of the filtered sirup were used for crystallization. Table I1 summarizes the count for the samples which were taken at different intervals. of Flat Sour Spores by Filtration a n d Crystallization NUMBER FLAT SOUR SPORES SAMPLE DESCRIPTION PER cc. OF SIRUP 1 Orieinal inoculated siruo -~ 25.000 2 First sirup through press 9;ooo 3 About 50 gal. (189.5 liters) through press 3,500 4 Average after all through first time 2,500 5 During second time through press 1,000 6 Average after all through second time 1,000 7 Average after all through third time 1,700 1,000 8 Average after all through fourth time 9 Composite 50 gal. (189.5 !item) sweet water 600 10 Mother liquor after centrlfuge 2,200 238O 11 Finished sugar 8 Spores per gram. Table 11-Removal
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The results indicate that a rapid and substantial decrease in contamination results from filtration. It also appears from the data that there is a point where the degree of contamination reaches a sort of equilibrium. There is also evidence that something more than actual mechanical filtration is operative in bringing about the reduction noted. Undoubtedly filtration and crystallization represent two of the outstanding phases of the sugar-refining operation tending to low thermophilic contamination. In the experiments cited, it appears that filtration is the more effective and it would appear to be the more important from the standpoint of positive elimination of the contamination. Of course it will be appreciated that the effectiveness of filtration or any other operation will vary under the many conditions which are possible. In a measure, every refinery may be considered to present a special problem and the problem in every instance will have to do not only with the removal of thermophilic bacteria but with prevention of accumulation. It seems quite certain that filtration, or treatment analogous to it, plays one of the most important parts, if not the most important, in removal of thermophilic spores. Accumulation may conceivably occur in points before or after filtration, and obviously the problem is complicated most when it occurs at subsequent points, as in the char filters or in storage of liquors. Bacteriological tests should show in any case the most sensitive points in the various operations.
December, 1931
Necessarily the problem of bacteriological control in the refinery can be treated only in a very general way here. Canning specialists are not usually relining specialists, and an intimate knowledge of relining practice is a primary requisite to intelligent treatment. It is known, however, from results observed that the question of thermophilic contamination of sugar has been successfully solved, and it is hoped that in the near future some of the agencies which have conducted intensive work on the subject d l make their results available. Material of this nature would possess distinct value in showing the way for specific treatment. Literature Cited (1) Barlow, 1913.
B..
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Uaiv. oi lllinoir, Master 01 Science 'Thesis io Botany,
. Esty, J . R , J . I,zj8iliour Dirmrrr, 27, 602 (1920). (2) Bigelow, W. D ~and (3) Cameron, E. I., Canning Trode. 1., 16 (March 17, 1030); The Conner, p. 17 (Mamh 15, 1930). ( 4 ) Cameron, E. J., and Esty, J . R.. I . Infrriious Diirosrs, 89, 89-105 (1920).
L'ALCHIMIST EN
c.,
( 5 ) Cameron, E. J., and Willi=ms, c. Canir. Baki. ParnriimL 11 A O ~ .76, , 28-87 (1928). ( 0 ) Cameron, E. J., Williams, C. C.. and Thompnon, R. 1.. Nstl. Cannm
(7)
A - ~ ~ nu& . , 261 (1~2s). ameron, E. J.. and yesail,I., conning A ~ p. ~230,
(March. 1831): Conning Trade. p. 18 (March 10. 1031); The Cnnnn, p. 16 (March 21. 1031); Pood Induilries, p. 266 (June. 1931). (*) Cheyney, E, w,, J , M L d , Rcrco,rk, lo, 177 (1910). (9) Dank, p. ,-, Bad., 373 (10) %ty, J . R., and stevenson, A. E.. J . ~ ~ f ~ ~ a i ~ 06,488 i~ r (1926). ~ (11) Pood Induslrics. Editorial, 9. 282 (July, 1931). J. (I2) lamer, L. 13**09 (1927). (13) James, L. H.. P o d Indlrlricr, p. 205 (November,1928). (14) Morrison, I,. E.. and Tenner. P. W., J. Bocl.. 7, 343 (1922). (15) ~ o r ~ i s ~ I.. a nE., . and n i t n u , F. w., ~ o i o n .~ a a . ,77, 171-185 (1924). (10) N h i i m i ~ lCaiioers Arrocn.. The Cannsi. p. 10 (April 4, 1931): Conning Axe. p~ 291 (April, 1931). (17) Nifional Canners Assocn., BuU. 96L.rev. (1931). (1s) O w e n W . L., Am. Bxpt. Sa.,Louisiana State Univ.. Bull. 1x6 (1911). (19) WBozirl, I.. J . M d Reieorih, 39, 340 (1910). (20) Weikman, C . A,. Agr. Expt. Sta.. Iowa State Coliege A S . Meeh. Arts, Bull. 111 (1929). (21) Werkman, C . H., and Weaver, H. I., Iv#a Slolr C d k c J . Sci., 2. 67-07 (1927).
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,%OITATION
This etching hy Andre Louis Victor Telrier (1776-1864) is credited by him to Th. With. The original painting from which this etching was made is in the State Art Gallery in Cussel, Germany, and hears the signature of Thomas Wijck. Photomaphic prints of this subject 8 by 10 inches can be ruppiied ai 82.50 ea&. had 10 by 20 inches at 66.00 each. Ordera and remittances should be sent t o D. D. Berolzbeimer, Editor, Thc Percolaior. 52 E. 41st St., New York, N. Y.
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