A Bacteriological Study of Ham Souring

Part 1

Transcriber’s Notes

Obvious typographical errors have been silently corrected. Several tables have been divided with duplication of the first column because of their excessive width.

Italics are represented thus italic.

Issued March 17, 1911.

U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ANIMAL INDUSTRY.—BULLETIN 132. A. D. MELVIN, CHIEF OF BUREAU.

A BACTERIOLOGICAL STUDY OF HAM SOURING.

C. N. McBRYDE, M. D., Senior Bacteriologist, Biochemic Division.

WASHINGTON: GOVERNMENT PRINTING OFFICE. 1911.

THE BUREAU OF ANIMAL INDUSTRY.

Chief: A. D. MELVIN. Assistant Chief: A. M. FARRINGTON. Chief Clerk: CHARLES C. CARROLL. Animal Husbandry Division: GEORGE M. ROMMEL, chief. Biochemic Division: M. DORSET, chief. Dairy Division: B. H. RAWL, chief. Inspection Division: RICE P. STEDDOM, chief; R. A. RAMSAY, MORRIS WOODEN, and ALBERT E. BEHNKE, associate chiefs. Pathological Division: JOHN R. MOHLER, chief. Quarantine Division: RICHARD W. HICKMAN, chief. Zoological Division: B. H. RANSOM, chief. Experiment Station: E. C. SCHROEDER, superintendent. Editor: JAMES M. PICKENS.

LETTER OF TRANSMITTAL.

UNITED STATES DEPARTMENT OF AGRICULTURE, BUREAU OF ANIMAL INDUSTRY, Washington, D. C., November 2, 1910.

SIR: I have the honor to transmit and to recommend for publication as a bulletin of this Bureau a paper entitled “A Bacteriological Study of Ham Souring,” by Dr. C. N. McBryde, senior bacteriologist in the Biochemic Division of this Bureau.

The souring of hams is a source of considerable loss in the meat-packing industry, and the cause of this trouble has heretofore been in doubt. Dr. McBryde’s paper presents the results of an exhaustive study of the subject, from which it appears that he has succeeded in discovering the true cause of the trouble. Besides a description of the experimental work the paper discusses methods of preventing the souring of hams and the proper disposal of those which have become affected.

Respectfully, A. D. MELVIN, Chief of Bureau.

Hon. JAMES WILSON, Secretary of Agriculture.

CONTENTS.

Page.

Introductory 7

Method of curing hams 8

Definition of souring 10

Classification of sour hams and location of sour areas 10

Method of detecting sour hams 12

Theories in regard to ham souring 12

Previous experimental work to determine cause of ham souring 13

The present experiments 14

Media employed 14

Method of procedure in examining hams 15

Part 2

Results of examination of sour and sound hams 16

Histological changes in sour hams 17

Chemical analyses of sour and sound hams 18

Bacteriological examination of sour and sound hams 20

Inoculation experiments with hams 21

Probable method by which ham-souring bacillus enters hams 33

Possibility of infection prior to slaughter 33

Possible infection from pickling fluids 34

Experiment to show whether infection takes place from the curing pickle 34

Possible infection through manipulation or handling 35

Infection from ham thermometers 35

Experiment to show whether hams become infected from ham thermometers 37

Infection from pumping needles 41

Infection from billhooks 42

Biological and morphological characteristics of the ham-souring bacillus 43

Conditions favorable to growth 43

Growth on different culture media 43

Morphology 46

Spore formation 46

Resistance to heat and chemical agents 47

Gas production 47

Acid production 48

Pathogenic properties 48

Nature of the bacillus 48

Prevention of ham souring 50

General summary and conclusions 53

Acknowledgments 55

ILLUSTRATIONS.

Part 3

PLATES.

Page.

PLATE I. Fig. 1.—Section of muscular tissue from sound ham, showing muscle fibers cut longitudinally; nuclei sharply defined and cross striation distinct. Fig. 2.—Section of muscular tissue from sour ham, showing muscle fibers cut longitudinally; nuclei undergoing disintegration and cross striation indistinct 16

II. Fig. 1.—Section through muscular tissue of ham which has undergone natural or spontaneous souring, showing distribution of bacilli between the muscle fibers, which are cut obliquely. Fig. 2.—Section through muscular tissue of ham which has undergone natural or spontaneous souring, showing individual bacilli between the muscle fibers, which are cut somewhat obliquely 18

III. Fig. 1.—Section through muscular tissue of artificially soured ham, showing distribution of bacilli between the muscle fibers, which are shown in cross section. Fig. 2.—Section through muscular tissue of artificially soured ham, showing individual bacilli between the muscle fibers, which are cut longitudinally 26

IV. Glucose bouillon culture in Smith fermentation tube at four days 48

TEXT FIGURES.

FIG. 1. Cross section through body of ham, with sour areas indicated by shading and dotted lines 11

2. Cross section through body of ham to show method of sampling for chemical analysis 18

3. Cross section through body of artificially soured ham, showing sour areas and points at which cultures were taken 25

4. Diagrammatic views showing construction of ham thermometer 36

5. Ham-souring bacillus (Bacillus putrefaciens), grown on egg-pork medium 46

A BACTERIOLOGICAL STUDY OF HAM SOURING.

INTRODUCTORY.

The souring of hams is a matter of considerable importance to those engaged in the meat-packing industry, and has been the occasion of no little worry, as in even the best-regulated packing establishments the yearly losses it entails are considerable. The subject has given rise to much speculation on the part of those engaged in the curing of meats, as to the cause of the trouble and how it may be remedied, and has received considerable attention in a practical way, but little seems to have been done in a scientific way toward determining the cause and nature of ham souring.

In a well-regulated meat-packing establishment the loss from ham souring is usually figured at about one-tenth of 1 per cent of the total weight of hams cured. At first thought this would seem but a small loss, but when one reflects that in a single large packing establishment some 3,000,000 hams are cured during the year, the loss, when figured out, is considerable. Taking 15 pounds as the average weight of a ham, 3,000,000 hams would represent 45,000,000 pounds of meat. Figuring the loss from souring on the basis mentioned, the amount of meat condemned and destroyed during the year would be 45,000 pounds. Assuming that hams sell at an average wholesale price of 15 cents a pound, the yearly loss for a single plant which cures 3,000,000 hams a year would be nearly $7,000.

While one-tenth of 1 per cent of the total weight of hams cured would represent the loss from souring in a well-regulated establishment, statistics obtained through Government meat inspectors show that 0.25 per cent would more nearly represent the loss for the entire country. During the fiscal year from July 1, 1908, to June 30, 1909, some 670,000,000 pounds of hams were placed in cure in packing establishments subject to Government inspection. Estimating the loss from souring at 0.25 per cent, the total amount of meat condemned and destroyed as sour would be 1,675,000 pounds. At 15 cents a pound the total annual loss from ham souring in packing houses subject to Government inspection would figure up something over a quarter of a million of dollars.

The problem of ham souring, therefore, is quite an important one from a practical and financial standpoint; but aside from these considerations it is also a subject of considerable scientific interest, and in view of the fact that all sour meats are condemned under the Federal regulations governing meat inspection it has seemed fitting that this question should be made the subject of scientific investigation on the part of the Bureau which is charged with the administration of this inspection.

The investigation reported in this paper has been conducted chiefly along bacteriological lines, and has been confined entirely to the wet method of curing hams, as this method is the one generally used in American packing houses.

METHOD OF CURING HAMS.

In order to make clear certain points in regard to the nature and occurrence of ham souring and to insure a better understanding of the experiments which are to be described later, it would seem best to begin with a brief outline of the method of curing hams as practiced in the larger packing establishments of the country. This description is merely a general outline of the method of preparing hams for cure and the method of handling hams while in cure, and deals chiefly with those points that bear on the question of souring.

After the slaughtered animal has been cleaned, scraped, eviscerated, washed, and split down the middle, the carcass is usually allowed to hang for an hour or so in a large room open to the outside air, known as the “hanging floor.” This is done with a view to getting rid of a certain amount of the body heat before the carcass is run into the chill rooms, and effects a saving in refrigeration.

The carcasses are next run into “coolers” or chill rooms, and subjected to refrigeration with a view to ridding them entirely of their body heat. The coolers are large rooms fitted with brine pipes and capable of accommodating several hundred carcasses. The temperature of the coolers when the carcasses are run in is about 32° F. When filled, the temperature of the cooler rises to about 45° F., owing to the heat given off from the carcasses. The temperature is then gradually reduced to 28 or 30° F. Hog carcasses are left in the coolers as a rule for forty-eight hours, at the end of which time they are stiff and firm, but not frozen. The temperature of the chill rooms is always carefully watched, thermometer readings being made every few hours and duly recorded. The temperature of the carcasses is always tested when they leave the chill room. In those plants provided with a hanging floor, a certain number of the carcasses are also tested before they are sent to the chill rooms in order to determine the amount of heat lost on the hanging floor.

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