December, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1243
Use of Sodium Nitrite in Curing Meats’ By W. Lee Lewis, R. S. Vose, a n d C. D. Lowry, Jr. DEPARTMENT OF SCIS$NTIFIC
RESEARCH, INSl’ITUTE
HE authorization of the use of sodium nitrite in curing meat by the Bureau of Animal Industry on October 19, 1925, through Amendment 4 to B. A. I. Order 211 (revised), gives increased interest to past and current work on this subject. The use of sodium nitrite in place of the accustomed sodium or potassium nitrates finds scientific and economic support. It is now generally accepted that the saltpeter added in curing meat must first be reduced to nitrite, probably by bacteria, before becoming available as a n agent in producing the desirable red color in the cured product. This reduction is the first step in the ultimate formation of nitrosohemoglobin, the coloring principle. The change of nitrate to nitrite is by no means complete and varies within considerable limits under operating conditions. Accordingly, the elimination of this step by the direct addition of smaller amounts of nitrite means the use of less agent and a more exact control. Earlier Investigations The scientific study of this subject dates from the work of Polenske,2 who found nitrites in cured meat and curing pickle. He was further of the opinion t h a t the nitrite was formed by bacterial reduction of nitrate. NothwangS confirmed the presence of nitrite, but attributed the reduction t o t h e meat tissue itself. The function of t h e nitrite was established by the work of Lehmann4 and Kisskalt.6 The former showed t h a t when fresh meat was boiled with nitrite in the presence of a little acid a red color, resembling cured meat, resulted. H e reported no similar result with nitrate. Kisskalt confirmed this, b u t proved t h a t with nitrate t h e color resulted if t h e meat was left in contact with the nitrate several days. As t o the nature of the coloring principle, Weller and Riegele obtained by ether extraction of sausage and other cured meats a red solution whose colored constituent in appearance and absorption spectrum resembled methemoglobin. They reported t h a t a colored extract could be obtained whenever nitrate had acted upon meat containing blood. Haldane’ made a more thorough investigation of this subject. By its absorption spectrum he identified the coloring matter of uncooked cured meat as nitrosohemoglobin. This substance had long been known as the product of t h e reaction of nitric oxide and oxygen-free hemoglobin. Herrmann,8 in 1865, had made it the object of a n extensive study, finding i t a relatively stable, deep red compound. The absorption bands of this substance in location resemble those of hemoglobin, methemoglobin, and oxyhemoglobin, but by exact work t h e spectra of t h e four substances are distinguishable. Haldane attributed the formation of nitrosohemoglobin t o the action of nitrite on the hemoglobin present in the blood and muscle tissues of t h e meat. H e showed by direct experiment t h a t nitrites react on blood t o produce nitrosohemoglobin and some methemoglobin, best in the absence of oxygen. The formation of nitrite in curing, in his estimation, was most likely t h e result of bacterial action, but not necessarily so. H e quoted Abelous and Gerard,Qwho had previously stated t h a t tissues free from bacteria have the power of reducing nitrates. Haldane further showed t h a t on boiling in solution nitrosohemoglobin is broken down into nitrosohemochromogen and globin. H e demonstrated t h a t t h e red color of cooked cured meat is,due t o this latter pigment. Received November 6 , 1925. Arb. kais. Gesundh., 7, 47 (1891); 9, 126 (1892). 8 Arch. H y g . , 16, 122 (4892). 4 Sitab. physikal. Med. Ges. Wurzberg, 4, 57 (1899). 5 Arch. H y g . , 36, 11 (1899). 6 Forschungb. Lebensmittel, 4, 204 (1897). 7.J. H y g . , 1, 115 (1901). 8 Arch. anat. physiol. Wissen. Med., 1866, 469. 9 Compf. rend., 129, 164 (1899). 1
2
OF
AMERICAN MEATPACKERS,
CHICAGO,
ILL.
In two papers, Hoaglund’o confirmed and extended t h e work of Haldane. H e studied nitrosohemoglobin carefully, showing differences in the appearance of crystals of this substance prepared from the blood of hogs, sheep, and cattle. H e studied t h e coloring matter of a large number of specimens of cured meat, and found t h a t t h e color of uncooked cured meat was not always due t o nitrosohemoglobin but might be occasioned by a decomposition product of this substance. probably nitrosohemochromogen. H e confirmed the findings of other investigators, that pickles after use in meat curing, and cured meats themselves, usually contain nitrites. H e suggested t h a t nitric oxide is an intermediate step between nitrates and the formation of nitrosohemoglobin, showing t h a t in pickle cellars pickles and meats sometimes became acid enough to give off traces of oxides of nitrogen. The demonstration of t h e intermediate formation of nitrite in meat curing suggested the employment of nitrite in place of nitrate as the curing agent. I n 1909 Glage,” in a practical book on curing, recognized t h e value of nitrites and recommended t h e use of partly reduced nitrate made by heating the dry salt in a kettle. He also colored sausage by a smoke containing nitric oxide. Several proprietary mixtures containing nitrite were put on the market-“nitrosin12 saltpeter,” “Au1a”’s salt, and “Lebbin” 1 4 salt, Auerbach and Ries,“ with the aid of a n improved method of nitrite determination, showed t h a t nitritecured meats often contained a n amount of nitrite far in excess of t h a t found in meats given a nitrate cure. Later Po1lak’‘j showed t h a t with careful control a nitrite cure was practicable, leaving even less nitrite in the finished meat than was usual with t h e nitrate cure. Auerbach and RiesL7subsequently accepted these conclusions.
Experimental To judge the desirability of curing meat with nitrite in place of nitrate, a series of parallel cures have been made with nitrite and with nitrate under packing-house conditions. I n each experiment one lot of meat was put down with salt, sugar, and sodium nitrate. X second lot of the same quality was given a cure identical in every way except that the nitrate was replaced by a smaller amount of nitrite. The progress of the cure was followed by repeated analyses of the pickle (where pickle was used) and the meat. Samples of the finished products from both cures were compared by competent judges. The work was carried out with the fullest cooperation of the Bureau of Animal Industry. Pork Hams
The first experiments were on hams cured in sweet pickle. Forty pairs of thoroughly chilled green hams were selected, having an average weight of 13 to 15 pounds and as near uniform size as possible. T o eliminate differences in the meat due to age, feeding, conditions of the animals, etc., they were carried through the cure in pairs-a left ham, for example, being given the nitrite cure, the corresponding right the nitrate, and the two again brought together for final judging. The pickles for nitrate curing were made up following t h e regular formulas of the plant in which the work was done; in the nitrite cure the usual nitrate of the formula was finally replaced by one-tenth its weight of sodium nitrite. Each ham was “pumped” with the proper pickle-that is, a few 10 BUY.Anrmal Industry, Annual Report, 1908,p. 301, J . Agr. Research, 3, 211 (1914). 11 Die Konservierung der roten Fleischfarbe,” Berlin, 1909. l p Ostertag, “Handbuch der Fleischbeschau,” Stuttgart, 1913. 1) Z . Fleisch und Milchhyg., 26, 4 9 (1915). 14 Lebbin, Swiss Patent 73.375. 16 Arb. Reichsgcsundh., 61, 532 (1919). 16 Z . angew. Chcm., 36, 229 (1922). 17 Ibid., 86, 232 (1922).
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
ounces of pickle were injected into the meat near the aitch bone of heavy hams and in the shank only of light hams. One-half of the hams were then put down in two tierces containing nitrite pickle, and the other half in tierces with nitrate pickle. I n each case the weight of the pickle was about half that of the hams. The temperature of the curing cellar was 38” F. After 5, 15, and 30 days the tierces were “overhauled”i. e., rolled and shaken so that the hams were set free from each other and the pickle thoroughly circulated between them. At 60 days the cure was terminated, the hams removed from the tierces, soaked several hours in water, and smoked. At the beginning of the cure, a t each overhaul, and a t the end of the curing period, samples of pickle from both cures were analyzed. The results are shown in Table I. I n addition, frequent nitrite determinations were made. T a b l e I-Analyses of Pickles, H a m Curing Interval NaNOz NaNOa NaCl Sugar PICKLE Days Sp. gr. Per cent Per cent Per cent Per cent A . Nitrite Pickles 0.12 Pump At start 1.20 24.4 3.65 0.049 At start 1.14 16.1 4.05 Cure 0.040 5 1.12 13.6 3.45 Cure 0.035 15 1.11 12.7 3.05 Cure 2.89 30 1.11 11.8 0.026 Cure 1.10 2.96 0.019 10.8 Cure 6P (end) E. Nitrate Pickles At start 1.21 0 2.22 24.1 3.53 Pump Atstart 0.66 1.14 0.0001 16.0 3.82 Cure 0.0001 0.55 5 1:12 13.4 3.44 Cure 0.0003 0.49 * 15 1.12 12.6 3.26 Cure 0.0040 0.47 11.8 2.91 30 1.11 Cure 0,0760 0.34 10.6 2.96 60 (end) 1.10 Cure
It will be seen that the rate of disappearance of salt and sugar is approximately the same in both cures. During the cure the nitrite content of the nitrite pickle slowly drops, while in the nitrate pickle it increases to a figure approaching (and sometimes exceeding) the amount of nitrite initially present in the nitrite pickle. At each overhaul and at the end of cure, determinations were made of the nitrite, nitrate, salt, and sugar content of the hams. Whenever a piece of meat was removed from a tierce, sufficient pickle was discarded to keep the meat-pickle ratio constant. The analytical results are given in Table 11. Interval Days 5 15 30 (a) 60 smoked ( 6 ) 60 smoked 5 15 30
60smoked ( b ] 60 smoked (a
T a b l e 11-Analyses of Hams NaNOz NaNOs NaCl Per cent Per cent ’ Per cent Nitrite Cure 0 0.91 0.005 0 2.34 0.003 0.004
0
0.005
0
0.005
0
Nitrate Cure 0.046 0.0001
0.0002 0.0020 0.0035 0.0050
0.071 0.009 0.131 0.126
Sugar Per cent
2.92 5.65 4.26
0.24 0.30 0.37 0.43 0.56
1.05 1.40 2.69 5.32 4.64
0.23 0.31 0.20 0.66 0.61
Vol. 17, No. 12
home economics specialists and experienced meat men on a score card which allowed 20 points for color, 60 for flavor, and 20 for texture. The judges did not know which hams had received the nitrite cure and which the nitrate. Some were boiled, some baked, some cut up and cooked in various ways. The final average of the scores recorded on six hams by nine judges was as follows:
. . .... ..
Nitrate-cured hams.. . . . , . . . . . . . .90.5 Nitrite-cured hams... . . . . . . . . . . . . . . . . . . . 9 2 . 0
I n an earlier experiment, identical in every way except that the usual sodium nitrate was replaced by one-third the amount of sodium nitrite, it was shown clearly that this amount of nitrite (in the pickle 0.2 per cent) was excessive. The cured hams contained 272 parts of sodium nitrite per million, and were graded below corresponding hams cured with nitrate, on account of inferior flavor. Beef Tongues
The satisfactory result of experiments with hams, using, in general, a ratio of 1 to 10, led to a study of the curing of beef tongues. Four hundred pounds of short beef tongues were soaked overnight in brine, and then put down, half with the usual pickle containing sodium nitrate and half with a pickle containing 1 ounce of sodium nitrite for every 10 ounces of nitrate in the control cure. The tongues in both cures were overhauled by rolling the tierces a t 10, 15, 20, and 25 days. At the end of 30 days all tongues were removed from the tierces, cooked, trimmed, and canned. The pickle was analyzed when prepared fresh, and on the days of the 20- and 25-day overhauls. The analytical results are shown in Table 111. More frequent determinations of nitrite were made. T a b l e 111-Analyses of Pickles, T o n g u e Curing Interval NaNOz NaNOa NaCI Sugar Days Sp. gr. Per cent Per cent Per cent Per cent Ni!ri!e Cure 0 20 25
30
1.15 1.09 1.09 1.09
0 20 25 30
1.15 1.10 1.09 1.09
0.060 0.028 0.020 0.024
0 0 0 0 Nitrate Cure 0.47 0.003 0.31 0.032 0.28 0.064 0.22 0.096
2.02 1.27 1.21 1.16
18.0 11.2 10.8 10.5
1.52 1.19 1.09 1.03
The nitrite determinations show, as before, a steady loss of nitrite in the nitrite pickle, and a building up of nitrite in the nitrate pickle to a n amount, in this instance, in excess of that present in the nitrite cure. Analyses of tongues from each cure were also made at the 20- and 25-day overhauls and at the end of the cure. T h e data are given in Table IV. Table IV-Analyses
Thus the finished nitrite-cured hams analyzed contained 45 parts of sodium nitrite per million, the nitrate-cured 35 to 50 parts. All contained much less than the maximum allowed in meat products by the Bureau of Animal Industryi. e., 200 parts per million. On boiling a partially cured ham the progress of color fixation is brought out. By this method it was found that color fixation in the nitrite cure proceeded much more rapidly than with the use of nitrate. At 30 days a boiled section of ham in nitrite cure showed red color almost to the center, while with a ham in nitrate cure the color development was approximately half complete. If sufficient salt can be introduced and the rest of the curing changes assured in a shorter time, the use of nitrite may make possible a reduction in the curing period. Cured hams were cooked uniformly and judged in pairs by
18.0 11.2 10.6 10.3
Interval Days
NaNOz Per cent
20 25 30
0.0020 0.0025 0.0045
of T o n g u e s
NaNOa Per cent Nitrite Cure 0 0 0 Nitrate Cure .
NaCl Per cent
Sugar Per cent
2.87 3.15 3.77
0.169 0.201
0.052 0.078 0.103
2.92 3.12 3.91
0.181 0.163
...
~~
20 25 30
0.0015 0.0050 0.0070
...
It will be noted that the amount of nitrite in the nitritecured t o n g u e 4 5 parts per million-is less than the amount present in the tongue cured in the usudway, which contained 70 parts per million. A few days after cooking and canning, tongues from the two cures were examined by canned-meat experts of several packing plants. They were not asked to score on a point basis,
December, 1925
I N D U S T R I A L A N D ENGIA’EERING CHEMISTRY
but to express a preference, considering color, flavor, and texture. All agreed that there were only slight differences in the products of the two cures. Of eight judgments, seven favored the nitrite-cured tongue, one the nitrate Beef Hams
Similar experiments were made on beef hams. Twentytwo green hams, weighing a total of 315 pounds, were put down with the plant’s regular nitrate pickle and a similar lot put down with one-tenth as much nitrite (in this case 0.06 per cent) in a pickle otherwise the same. The tierces containing the hams were overhauled a t 15, 30, 45, and 60 days, and the cure terminated a t 75 days. At the end of the cure the hams were soaked in water and smoked. Nitrite determinations were made on the pickle a t frequent intervals during the care and complete analyses a t the beginning, a t the 60-day overhaul, and a t the end of cure. The usual loss of nitrite from the nitrite pickle and rise of nitrite in the nitrate pickle were observed, with, however, a decrease in nitrite in the nitrate cure toward the end of the curing period. The nitrite-cured hams contained 13 parts of nitrite per million, nitrate hams the same amount. Cured hams were judged by five persons. They all stated that the samples from the two cures were practically identical. Three gave a slight preference to the nitrite-cured product, while two preferred the nitrate cure. Dry Curing
In addition to these experiments in sweet pickle curing, a study was made of the adaptability of sodium nitrite to the “dry” or “box” cure of bacon, in which green bellies are rubbed with a mixture of salt, sugar, and nitrate, packed in boxes, and allowed to remain approximately a month for curing. Two 600-pound boxes of bellies were put down. For one, the plant’s regular curing mixture was used, a t the rate of 5.5 pounds per hundred pounds of meat. I n the cure of the other box, a curing mixture was used in which 1 ounce of sodium nitrite replaced 10 ounces of nitrate in the usual cure, using 5 pounds 4 ounces of this mixture per 100 pounds. Analyses of the two mixtures are shown in Table V.
1245
T a b l e V-Analyses of Dry-Curing Mixtures, Per c e n t NaNOo NaN03 NaCl Sugar Nitrite cure 0.5 55.48 44.12 Piitrate cure 0.0001 4:80 53.73 41.48
The cure was terminated, and the bacon soaked in water and smoked a t the end of 25 days. Determinations of nitrite, nitrate, and salt were made on a sample from each cure, with results as shown in Table VI. Table VI-Analyses Nitrite cure Nitrate cure
of Box-Cured Bacon, Per c e n t NaNOa NaNOs NaCl 0,0004 None 1.58 0.0010 0.058 2.42
Both samples are seen to be exceedingly low in sodium nitrite. The four persons judging the quality of the finished products were asked to grade samples from the two cures, first and second. Two samples were submitted from each cure. . I n one case nitrate bacon was preferred, in the other nitrite. There was quite evidently no real basis for distinction between the two cures. Other Experiments
Several other nitrite-curing experiments were made in none of which was the legal limit of 200 parts of sodium nitrite in the finished product even approached. I n two cases the nitrite content of the meat was highest a t about the middle of the cure, decreasing toward the end. I n every study the nitrite-cured meats were compared with meats cured in the regular way with nitrate, and in no case was any real difference in quality found. Conclusion
Working on a significant scale in several packing houses it has been shown that when carefully used, smaller amounts of sodium nitrite, in round numbers, one-tenth the amount may successfully replace the usual nitrate in curing hams, bacon, tongues, and beef. Much work remains to be done before the new agent can be applied with assurance to all types of cured meats. Packing plants should approach the new agent on a carefully controlled experimental basis with the close cooperation of their chemist and the government inspector in charge.
I n t e r n a t i o n a l C o m m i t t e e s on Organic a n d Inorganic Chemical Nomenclature at Paris in October, 1925 Left to right, standing: A. J. Greenaway, Great Britain F. Fichter, Switzerland A. M. Patterson, United States A. Pictet, Switzerland M. Delcpine, France C. S. Gibson, Great Britain R. Marquis, France Sitting: W. P. Jorissen, Netherlands (chairman inorganic) A. F . Holleman, Netherlands (chairman organic)
