Operation of Vinegar Generators RUDOLPH J. ALLGEIER, REUBEN T. WISTHOFF, AND FRANK M. HILDEBRANDT U. S. lndusfrial Chemicals Co., Division o f Nafional Distillers Producfs Corp., Balfimore, Md.
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HE operation of vinegar generators is very largely an empirical matter, as is evident from the lack of published information on the subject This fact points t o the need for studies that might lead to improvements in the efficiency of conversion of alcohol and to an improved vinegar aroma, which is the quality factor of interest to the manufacturer. A small scale Frings-type generator which gives results applicable t o commercial units has. been employed in studies of various factors important in the operation of full size generators. The present paper deals with two such factors. One is the economics of using an alcohol denatured with ethyl acetate (S.D. 35A), as users have questioned whether this denatured alcohol gives as high a yield of acid, gallon for gallon, as undenatured alcohol or certain other denatured formulas. The other is the effect on the activity of the acetic bacteria of small amounts of heavy metal salts dissolved as contaminants in the circulating charge.
DENATURED ALCOHOLS AS GENERATOR FEEDS The Congress of the United States in 1906 enacted the “Denatured Alcohol Law” authorizing the addition of various denaturants to ethyl alcohol. This ruling allowed manufacturers t o obtain alcohol denatured a t the distillery by the addition of an ingredient or ingredients which did not interfere with their specific processes, yet gave them a tax-free use of industrial alcohol. Three such specially denatured formulas have been employed in the manufacture of vinegar-S.D. 18,S.D. 29, and S.D. 35A. The U. S. Industrial Chemicals Go. has made available t o the trade a 35A denatured alcohol in which certain still fractions known t o improve vinegar aroma are present. This is marketed as 35A Special. This investigation represents an extended study of S.D. 35A, regular and special, S.D. 18, S.D. 29, and 190-proof undenatured ethyl alcohol as feed for the production of acetic acid in Fringstype generators. The efficiency of conversion and the aroma of the product were determined for the various formulas during a period of 7 months.
the commercial Frings type in construction and operation characteristics, and it has been shown that the results obtained on them may be applied to full sized generators. The operation of the large Frings-type generator in a vinegar plant consists of a cycle beginning with the introduction of a charge, followed by a period of fermentation t o convert the alcohol to acetic acid, then by a withdrawal of a portion of the product, after which the generator receives a fresh charge to start the cycle again. The small scale equipment mentioned above is operated in this same fashion. A 7-day cycle is used, consisting of the introduction of the charge, the conversion period, and the withdrawal of the product as in the large type. The experimental generator is then recharged and the operation repeated. The conditions of aeration, temperature control, concentration of feed, and method of operation are the same as employed in previous experiments (1). All the formulas were prepared according to U. S. Government specifications. T o make 35A, 5 volumes of 85 t o 88% ethyl acetate (technical) were added to 100 volumes of 190-proof alcohol. The experimental S.D. 35A Special was similar to the regular plant production of this formula. S.D. 29 was denatured by adding 5 volumes of an alcoholic solution containing 20% acetaldehyde to 100 volumes of alcohol. S.D. 18 was made by adding 100 volumes of vinegar, containing 9 grams per 100 ml. of acetic acid, t o 100 volumes of 190-proof alcohol. All the above formulas were diluted with t a p water t o 9 grams of alcohol per 100 ml. of solution t o make the generator feed. Two liters of this dilute feed were used in each charge. A fermented solution of Diamalt, a malt concentrate manufactured for bakers (by Standard Brands, Inc.), was added as a nutrient. This nutrient, which has proved very satisfactory, is made by fermenting a solution of Diamalt (15 grams per 100 ml.) with yeast, filtering through No. 12 Whatman paper, and adding 25 ml. of the filtered solution to the 2000 ml. of diluted alcohol charge.
V e r i ous Denatured Alcohols Gave Practically Identical A c i d Production The duration of the experiments herein reported was 7 months Table I shows the monthly average of acetic acid and residual alcohol produced. Table I1 shows the monthly average of per cent efficiency on alcohol charged. The calculation of the data in these tables has been explained ( 1 ) . The curves in Figure 1 show the comparative performance of the generators on different formulations in terms of the Special S.D. 35A control generator as 1 0 0 ~ o . This procedure corrects for variations t h a t occur in the battery as a whole. The efficiency figures shown by the curves in Figure 1 represent a moving average of four weekly determinations in order to eliminate minor week-to-week changes in any one generator. The latter method of handling the data has the effect of making the acclimatization period appear longer than is shown in Table 11.
Small Generator Operated Under Same Conditions and Used Same Type Charge as Production Equipment The experimental technique employed in these studies is mentioned in a previous publication ( 1 ) . The pilot plant scale generators have been described by Hildebrandt (%), and used successfully by the authors in their past experiments. The only major improvement since the last publication (1)was the enclosure of the generators in a room which is thermostatically controlled t o maintain 30’ f 0.5” C. These batteries of generators are like 489
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INDUSTRIAL AND ENGINEERING CHEMISTRY Table 1.
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Acetic Acid Production and Residual Alcohol during Test Period
-4ugust average includes one week in September.
Table II. Month 1951
Per Cent Efficiency on Alcohol Charged
Special S.D. 3 5 8
S.D. 35-4 S.D. 29 S.D. 18 85.93 86.95 86.66 87.04 February 83.88 83.33 86.63 87.06 &farc h 86.96 87.32 85.21 86.72 April 86.88 87.27 86.46 86.91 May 86.66 87.64 87.02 87.51 June 87.38 86.52 85.78 86,77 July 86.29 85.48 86.83 86.25 Augusta August average includes one week in September.
Undenatured Alcohol 86.31 86.70 86.19 86.13 86.58 84.71 84.58
Table I11 gives the monthly and over-all averages of alcohol fed and acetic acid produced in each cycle of the generators on 35A and undenatured alcohol, respectively. This table is the basis for a comparison of vinegar production from S.D. 35A and 190proof undenatured alcohol.
Table 111.
Average Alcohol Fed and Corresponding Production of Acetic Acid per Cycle
S.D. 35A 190-Proof Alcohol. Absolute alcohol Acetic acid Absolute alcohol Acetic acid fed, grams produced, grams fed, grams produced, grams 180.20 202.21 201.71 180.80 Fehruai'Y 180.80 203.76 204.52 180.80 March 180.43 202.16 203,74 180.05 April 180.30 202.00 203.63 180.16 Nay 180.40 203.05 204.19 180.00 June 180.50 198.93 203.25 180.00 July 180.00 197.80 202.52 180.00 August Average 180,26 203.37 180.38 201.47 hIonth 1951
Special S.D. 35A Charge Formula Produced Vinegar with Best Aroma The aroma of the vinegar produced, one of the most important considerations, was followed carefully in the products of these experimental runs. Odor tests were made by a panel of five or inore observers, on coded samples, in order to obtain unbiased judgments. The vinegar from special S.D. 35A was considered best, regular S.D. 3 5 8 second, S.D. 18 third, and S.D. 29 fourth; that from undenatured alcohol was considered to be lacking in character. The results agree tvell with previous odor tests on these types of vinegar. Allowing for a 6-week period of acclimatization to the feed, no significant difference was noted in the average efficiencies of the generators fed the various denatured alcohols. The effect of acclimatization was more pronounced where S.D. 18 and S.D. 29 were used than in the case of 358 regular and special. In the S.D. 18 and S.D. 29 alcohols the denaturants mere widely different in composition from those of S.D. 358. The undenatured alcohol average efficiency, however, was 1.470 lower than the others, which is beyond the range of differences attributable to experimental error. The comparative results, shown in Figure 1, averaged as follon~: Special S.D. 35A Regular S.D. 3SA S.D. 29 S.D. 18 Undenatured alcohol
100.00% (control) 100.05% 99.52%
KO appreciable difference in the rate of production of acetic acid was noted. The higher acetic acid content of the S.D. 18 generator (see Table I) was due to the fact that some acetic acid was added with the feed. It does not represent a better oxidation. Formulas S.D. 18 and S.D. 29 are not generally used a t present for vinegar production. The former has been eliminated because of the cost of shipping quantities of vinegar equal to t,he alcohol supplied by the denaturing plants for the formula. S.D. 29 contains acetaldehyde which is very volatile and therefore difficult to handle in large quantities under plant conditions, The question as to whether the ethyl acetate in the S.D. 35A formula is converted to acetic acid, as is the ethyl alcohol, is ansvvered in this study. An andlysis of Table 111 shows that the yield of acetic acid from S.D. 358 either regular or special and that from 190-proof.alcohol are the same, gallon for gallon, within experimental error. Actually, the amount of acetic acid produccd per unit volume of denatured formula used in t.hese two types of feed agreed within 0.5y0, as is shox-n in the following calculation. S.D. 35A has a specific gravity of 0.8186 at 6O0/6OoF., .il-eighs 6.817 pounds per gallon, and contains 90.67% alcohol by weight, including the alcohol equivalent of the ethyl acetate used t o denature. 190-proof alcohol has a specific gravity of 0.8158 a t 6 0 ° / 6 0 0 F., w-eighs 6.794 pounds per gallon, and contains 92.42% alcohol by weight. From these data it is possible to calculate that 1.3475 ml. of S.D. 35A and 1.3263 ml. of 190-proof alcohol each contain 1 gram of absolute alcohol. Reference to Ta.ble I11 shows that on the overage 180.26 grams of alcohol in 35A produced 203.37 grams of acetic acid, and 180.38 grams of undenatured alcohol produced 201.47 grams of acetic acid. I n the case of t,he 35,4, the alcohol charge included that resulting from the saponification of the ethyl acet'ate used to denature. On thi8 basis, 180.26 grams of alcohol is contained in 180.26 X 1.3475 ml. of 35A, or 242.90 ml. of 3 5 h . Thus we have 0.8373 gram of acetic produced per milliliter of 3 5 8 . A corresponding calculation for 190-proof shows 0.8421 gra.m of acetic produced per milliliter of 190-proof. These productions agree t o -within about 0.5y0, as state-1 above, and prove experimentally that volume for volume, the 3SA produces as much acetic acid as pure 190-proof alcohol. The ethyl acetate denaturant has always been a matter of concern t.0 users of 35A, as it has been felt that it represents a loss so far a? acid production is concerned. This work, however., shows that the combined alcohol of the ester may be considered as part of the alcohol available for acetic production when S.D. 3 5 h is used.
EFFECT OF HEAVY METALS ON VINEGAR PRODUCTlON It has been known for many years that the heavy metals are of tremendous biological importance. With certain organisms sothese metals are active in extremely minute amounts-the called oligodynamic effect. For instance, in the case of green algae, trace amounts of copper are highly toxic, while for bacteria, silver is extremely toxic. Recently, it has been shown that the heavy metals have a place in the functioning of enzymes and that certain specific elements are found in either the enzyme molecule
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of a fresh alcohol charge, then builds up to the final concentration at the end of the cycle, only to be lowered again after withdrawal of part of the charge and addition of a fresh batch of feed. The generator has a certain liquid holdup and this, together with changes induced by additions and withdrawals and by the activity of the organisms, prevents establishment of a constant level of any material in the liquid circulating from the reservoir over the chips. The approach which seemed most reasonable as a means of testing metal effects was t o add an appropriate metal or metal salt to the circulating liquid in the generator at the same time that the alcohol was put in. This addition was repeated a number of times in order to build u p a concentration of the metal, and when the generator showed a response in decreased acid production the addition was stopped and the generator was continued in operation in order to see whether it would recover. This process was repeated at several concentration levels in order to get some idea of the tolerance of the organisms to the metal in question. Judgment as to toxicity can be based on the original response and the rate and degree of recovery.
Metals Concentration Must be Related to Biological Reactions and to Time
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or coenzymes (3, 4). I n addition to these activities, which may be considered a part of the normal functioning of the organism, heavy metals present in considerable quantities are poisonous. This is especially true of lead, which must be eliminated from food for human consumption and from products which are generally t o be used in contact with living cells. It is obvious that the relation of metals to the activity of vinegar organisms may well be of interest because vinegar manufacture involves pipes, pumps, and storage tanks, all of which may be made of metal. This is especially true because the use of the Fringe-type generator has become practically universal. I n this equipment, pumping and cooling the charge are a necessary part of the operation and suitable pumps and piping are a part of the generator assembly. Wustenfeld ( 5 )states that lead, copper, iron, aluminum, and zinc are most easily attacked by vinegar and vinegar fumes and that the salts of these metals are injurious to health or poisonous to humans. He suggests the utilization of tin, chromium, nickel, steel, and high-silicon iron alloys as best for vinegar installations. Other articles of a similar nature are cited in Deutsches Essigindustrie, a German publication devoted exclusively t o vinegar production. This paper presents experimental results showing the effect of heavy metals on the activity of vinegar generators. It is concerned rather with their poisonous action than with what might be called normal metallic relationships, such as those noted above in the case of enzymes. A study of the effect of a metal salt addition on a generator operated as noted above poses a problem as to the manner of adding the substance under investigation. It is obvious that the conditions in the generator are always changing. The starting concentration of acetic acid is lowered upon addition
The fact that conditions change during the cycle raises a question as to how much metal is in contact with the organisms. It was felt that the best basis for establishing this concentration was to calculate the metal in the circulating liquid on the basis of the measured salt additions, the generator holdup, the added feed volumes, and volumes withdrawn. All these quantities are known. In order t o check these calculated quantities of the metallic elements, samples of the circulating liquid were analyzed a t intervals for actual amounts of the various metals. An excellent agreement between the actual analyses and the calculated amounts was obtained. The experimental situation is as follows: We have a miniature Frings-type generator containing circulating liquid in which there is a gradually increasing concentration of a metal salt over such a period as is necessary t o initiate response in the organisms of the generator. Once a marked response is observed, additions of themetal salt are discontinued, resulting in decreasing concentration of the metal. This is the recovery period for the organisms in the generator. On the biological side, the reaction of the generator t o the metals is indicated by several factors. The efficiency of the conversion of the alcohol to acetic acid decreases as a consequence of a decrease in the acid produced, and the residual or unconverted alcohol in the generator may increaEe, as the cycle time is held constant. In some cases, the alcohol disappeared without forniation of the expected amount of acetic acid, whereas in other cases it was obvious that the organisms had stopped short of complete conversion of the alcohol in the feed. All of the various factors involved in the experiment-namely, the changes in dosage of metal and the biological reactions of the generator as indicated by the measurements noted above-take place over a time period, and the problem arises of relating the dosage us. time to the biological reactions us. time. The experiments covered by the work reported herein extended over a period of several years. The cycle time was 1 week. Consequently, there are many individual observations on all the aspects of the generator operation. Involved in the experiment are lead, copper, iron, zinc, and tin. Each metal was used in a different generator and a sufficient number of dosage levels was tested in the case of each one t o get the metal toxicity established. Some consideration was given to the absolute level of toxicity, and in those cases where the organisms were relatively indifferent t o metallic concentrations up to 100 p.p.m. no further levels were tested, as it seemed that toxicities due to an amount of metal beyond 100 p.p.m. would be of no particular interest to vinegar producers. Such levels would not be met in practice. When re-
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covery did not take place, the generators were repacked and fresh organisms were used for further experiments. The large number of individual measurements involved in these experiments makes it undesirable t o present results as tabulations of dosages and responses for individual cycles. Consequently, the work is presented in a series of graphs (Figure 2 ) . These graphs show the metal dosage US. time and the biological responses vs. time; the same time scale has been used for both. In the plotting of the metal dosages, the same scale has been used throughout for parts per million and it is obvious that there are very large differences in amounts of the metals tolerated by the organisms. The rate at which recovery took place is related t o the concentration of metal in contact with the organisms in the generator and to the length of time of such contact. The denatured alcohol used in these experiments was S.D. 35A. This formula is prepared by adding 5 parts of 85 to 88% ethyl acetate (technical) to 100 parts of 190-proof alcohol by volume. This denatured alcohol was diluted with water to a concentration of 9 grams of alcohol per 100 ml. of feed. A fermented solution of a malt concentrate was added a8 a nutrient. This nutrient is made by fermenting a solution of the concentrate (15 grams per 100 ml.) with yeast, filtering through a coarse paper, and adding 25 ml. of filtered solution to the charge for the generator, which is 2000-ml. volume. The presentation of the data from the experiments in the graphs is uniform for all the nfetals investigated. It consists of a graph giving the metal concentration as parts per million in the circulating liquid. I n addition, a curve is given showing the efficiency of conversion as a solid line and expressed in terms of the control generator, containing no metal salt, as 100 in order to rule out factors affecting the whole battery of generators. A curve giving the per cent residual alcohol is shown along the same axis as the efficiency and the metal dosage. The arrows on the two curves of each group point to the respective abscissa and ordinate scales for the pertinent data. Details of the calculations used t o arrive a t the efficiency figures shown on these graphs have been published ( I ) , as well as a detailed description of methods of analysis of both feed and product. Results Established the Approximate Toxicity Threshold of Five Metals
Iron. The experimental work on iron was carried out in two series of runs made at different times, in different generators. In the first, the iron was added to the circulating liquid in the generator in the form of a finely divided powder. This was done after some preliminary experiments had shown that a coarser form of the metal did not dissolve promptly. Because iron may be considered a relatively nontoxic material, i t was used in rather large amounts in the first run. As will be seen from the graph, the concentration was increased rather rapidly to 348 p.p.m. At this time it was apparent that the generator was reacting very definitely t o the metal, as may be seen from the drop in the efficiency curve and the rise in the curve of residual alcohol corresponding to the rise in the dosage. Consequently, the addition of metal was discontinued and a t the end of 16 weeks the generator had reached a very low iron content, as shown on the graph. The amount of iron shown by the shaded area on the graph is over and above any iron that was in the water and in the nutrient solution used. Iron in the large quantity used in this experiment resulted in incomplete utilization of alcohol, but the organisms in the generator were apparently not harmed in any permanent way, as recovery was reasonably prompt and ultimately the generator performance came back practically to the same value as the control generator. This is indicated by the rise of the efficiency line to the 100% point following discontinuance of iron additions. Although this generator was exposed to very high concentrations of the metal, the exposure was for a relatively short period of time.
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I n the second series, in which iron was used in the circulating liquid, the metal was added in the form of ferric tartrate, with the idea of getting a more rapid solution and a more complete distribution through the circulating liquid. The acetate might be considered the most logical salt to use but it was not readily available, and is relatively insoluble. I n this experiment and in the others where salts were added to the generator liquid, the 2000ml. charge was used as a solvent for the salt addition employed in any particular cycle. The graph shows the actual concentration of the metal and not the concentration of the salt. The behavior here is somewhat different from that shown in the first experiment. The metal concentration was lowered considerably, but was maintained for a longer period. Reaction, as shown by the falling efficiency line, was not as rapid as before, but apparently the long period of exposure affected the ability of the generator to recover. Salt addition was discontinued a t 17 weeks and the generator reached a minimum iron content a t 27 weeks. At that time there had been some recovery but not quite enough to equal the efficiency of the control generator. In spite of the low efficiencies a t the end of the dosage period, and the recovery to only 95’%, the residual alcohol is practically nil throughout the latter part of this experiment. This would indicate that the alcohol was either used t o produce something other than acetic acid or that acetic acid itself was oxidized t o carbon dioxide and water. Further work would be needed to throw light on the reason for this behavior of the generator. Copper. Three experimental series were run in which thismetal was added to the generator liquid. In the first series, finely divided metallic copper was put in the circulation tube, with the expeeption that it would dissolve and be distributed through the generator as the acetate. However, the metal did not dissolve rapidly and the experiment gave erratic results. This series, therefore, served only to indicate a dosage level and is not shown on graphs, as are the two succeeding runs. The second series was treated with cupric acetate. The dosage was rather large and there was an immediate and severe reaction, as shown both by the efficiency and residual alcohol curves. The salt was not added after the ninth week, a t which time it was at B level of 46 p.p.m. in the circulating liquid. Following discontinuance the efficiency and residual alcohol continued to drop. There was no sign of recovery from the high level of copper. At 19 weeks the copper content of the circulating liquid was down practically to zero, but the organisms in the generator had evidently been injured to such an extent by the long exposure to high copper concentrations that recovery was impossible. Operation of the generator for several weeks beyond the point a t which the metal concentration was zero failed t o show any recovery of the organisms, and the experiment was discontinued. This generator was brought back to normal by reinoculation without repacking. A third series was run using cupric acetate as in the second series. In this case, because the second run had shown such a sharp reaction due t o high concentration of the metal, the dosage was nldde light a t first and copper content gradually was raised to around 20 p.p.m. a t 15 weeks. About 2 weeks after the metal had reached the 20 p.p.m. level, the efficiency started to fall off, and metal addition was discontinued at 22 weeks. B y the 30th week the concentration of copper had fallen to practically zero, At this same time the efficiency of conversion of alcohol was back t o normal and the residual alcohol was also normal; therefore there had been no permanent injury of the organisms by exposure, as indicated in the graph for the third run. Lead. Three series of experiments were carried out with this metal. The first one employed finely divided metallic lead in the circulating liquid and the second and third used basic lead acetate dissolved in the charge, as was noted in the case of the other tests with metals. The first experimental series using finely divided lead was run a t a relatively
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high concentration of the metal, as will be seen from the graphs. At the end of 9 weeks the circulating liquid contained 96 p.p.m. of lead. From the beginning of lead addition, the generator fell off in efficiency and after the metal was discontinued, i t was kept in operation until the fourteenth week. As there was no sign of recovery, it was decided to stop the experiment a t this point and repeat with a lower concentration of the metal. The behavior of this generator was consistent in that it reacted sharply to high lead concentration, by both a fall in efficiency and a corresponding rise in the residual alcohol. I n the second experiment with lead, basic lead acetate in low dosage was used a t the start and then a higher dosage was added. At 2 weeks the lead content was a t 26 p.p.m., where it was held for 4 weeks. During this period, the efficiency of the generator dropped and then recovered somewhat. Consequently, the concentration level of the metal x a s raised to 46 p.p.m. At the fourth week employing this concentration, a sharp reaction occurred in the efficiency and there was a corresponding rise in the residual alcohol found in the product a t the end of the cycle. Rate of addition of lead was again changed so as to reduce the concentration to 30 p.p.m. by the fifteenth week. The efficiency continued to drop and at that point the addition of metal salt was discontinued. I n about 2 weeks after the discontinuance of metal additions, when the lead concentration had fallen to 14 p.p,m., the generator began to recover. At 24 weeks the metal concentration was practically zero and a t 30 weeks the generator had completely recovered, with conversion efficiency practically equal to control and typically low residual alcohol values. The third series with lead was run a t a very low concentration over a long period of time. The actual amounts involved may be seen from the graphs. The lead addition was discontinued completely a t 23 weeks and the generator was operated until the 30th week. Evidently, the conversion efficiency of this generator was affected to some extent and the toxicity of the metal here shows in the form of the well-known cumulative effect of lead. There was no marked effect on the residual alcohol. Zinc. The experiments with zinc show that the organisms are not particularly susceptible t o this metal. Only a slight lowering of efficiency was produced when the metal concentration was raised t o 99 p.p.m. When the zinc additions were discontinued, the generator recovered completely by the time the metal had fallen to the zero level. This metal was added in the form of zinc acetate. Tin. The experiment Fith tin was carried out with stannous tartrate. This salt was used because it is readily prepared and is sufficiently soluble for the purpose. As in the case of zinc, it was possible to run up the concentration of tin t o 97 p.p.m. without any detrimental effect on either the conversion of alcohol or the residual alcohol in the fermenting solution. At 18 weeks the experiment was discontinued.
A Toxic Dosage of Metals Decreased Efficiency of Process and Increased the Amount of Residual Alcohol The following reaction characteristics were noted in the generators involved in this experiment: I n all cases a toxic dosage of the metals resulted in an efficiency decrease, accompanied in most cases by a corresponding rise in residual alcohol. \T7hen the
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toxicity was pronounced, the concentration of acetic acid in the draw-off was directly, and the residual alcohol inversely, proportional to the dosage. I n a few cases the alcohol disappeared without a corresponding production of acid. An analysis of the results discloses that the relative toxicity rating of the metals tested is in the order of lead, copper, iron, zinc, and tin. The threshold of toxicity is approximately as follows: 10, 15, 50, 100, and greater than 100 p.p.m., respectively.
Summary The denatured alcohols most used in vinegar manufacture were compared in pilot plant equipment operating in a manner similar to Frings-type commercial generators. The results establish the fact that the various denatured alcohols give practically identical acid production. It was demonstrated that, gallon for gallon, the formula denatured with ethyl acetate (S.D. 35A) was equivalmt to undenatured alcohol as a raw material for vinegar production. This finding answers the question as to whether ethyl acetate is converted to acetic acid as is the ethyl alcohol. Vinegar aroma mas improved by the use of the formula. Odor comparisons on the finished vinegars were made and the sample from Special S.D. 35.4 was considered best, from regular S.D. 35A second, from S.D. 18 third, and from S.D. 29 fourth; that from undenatured alcohol was considered lacking in character. An investigation of effect of lead, copper, iron, zinc, and tin on the activity of vinegar generators covered a period of 2 years. The results establish the approximate toxicity threshold of the five metals as follows: lead 10, copper 15, iron 50, zinc 100, and tin greater than 100 p.p.m. In all cases a toxic dosage of the metals resulted in a decrease in efficiency, accompanied in most cases by a corresponding rise in residual alcohol. When toxicity was pronounced, the acetic acid concentration in the draw-off was directly, and the residual alcohol was inversely, proportional to the dosage. The rate a t which recovery of a generator took place is apparently related to the concentration of metal in contact with the organisms in the generator and t o the length of time of such contact. These experiments are part of a series of studies concerning the factors affecting the performance of vinegar generators. Further investigations are suggested on the degree of chlorination and biological purity of the dilution water, the nutrients added, the the effect of “overoxidation,” the factors leading to improved aroma, and various other elements involved in vinegar manufacture. Continuation of these studies might be expected to raise production levels and improve the quality of the product. Literature Cited (1) Allgeier, R. J., Wisthoff, R. T., and Hildebrandt, F. M., IND. ENG.CHEIM., 44, 669-72 (1952). (2) Hildebrandt, F. M., Food Inds.. 13, No. 8, 47-8 (1941). (3) Lehninger, A. L., Physiol. Rev., 30, No. 3, 393-429 (1050). (4) Porter, J. R., “Bacterial Chemistry and Physiology,” pp. 451614, New York, John TViley & Sons, 1946. (5) Wustenfeld, H., “Lehrbuch der Essigfabrikation,” pp. 70-1, Berlin, Paul Parey, 1930. RECEIVED f o r review April 28, 1952.
ACCEPTED September 2 0 . 1 9 3 2 .
