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.

The carcasses are tested by means of an especially constructed thermometer, known as a “ham thermometer,” which has a pointed metal protector so that it can be thrust into the body of the ham. (See fig. 4.) The ham has been rightly selected as the proper portion of the carcass at which to take the temperature, as it constitutes the largest mass of muscular tissue in the carcass and holds the body heat longer than any other portion. In taking the temperature, the thermometer is thrust deep into the body of the ham so that the point of the thermometer rests alongside or a little behind the upper portion of the femur or middle bone, the latter being used as a guide in introducing the thermometer. A certain number of the carcasses from each cooler are tested in this way as a check on the refrigeration. The inside temperature of the hams when they leave the chill rooms should be about 34° F.

The carcasses are next cut up and the hams trimmed for pickling. In some houses the hams are given an additional chilling of 48 hours after they are cut from the carcasses, but this is not done as a rule, nor does it seem to be necessary.

The hams are now sent to the pickling rooms, or “sweet pickle department,” as this branch of the packing house is designated, and here a certain number are again tested with a thermometer, as described above. This test is carried out by the foreman in charge of the sweet pickle department in order that he may satisfy himself that the hams are properly chilled before they go into the pickle and as an additional check on the refrigeration.

The hams are now ready to be “pumped,” and this pumping, as will be shown later, constitutes an important step in a successful cure. Pumping consists in forcing a strong brine solution containing saltpeter into the muscular tissues of the ham, and is accomplished by means of a large, hollow, fenestrated needle connected by means of a rubber hose with a powerful hand pump. The needle is introduced along the bone, the latter being used as a guide.

In all of the larger packing establishments two general methods of curing hams are followed, the two methods being designated as the “fancy” or “mild cure” and the “regular cure,” the term “cure” being used to designate the curing period. Various trade names are given by the different packing establishments to the hams cured by these methods. In the fancy cure the hams are pumped in the shank only, whereas in the regular cure they are pumped in both body and shank. The same pumping pickle is generally used for the two cures. It is a significant fact that the greater proportion of the “sours” are found among the fancy or mild cure hams. This point will be discussed farther on in connection with some experiments to be described later.