A bacteriological study of ham souring

by Charles Neil McBryde

In these two experiments it was proven beyond doubt that the anaerobic bacillus isolated from sour hams was capable of producing souring when introduced into the bodies of sound hams; and in view of the fact that this bacillus was constantly present in hams which had undergone spontaneous or natural souring, and was the only organism that could be isolated from such hams that was capable of producing in egg-pork cultures the characteristic sour-ham odor, the conclusion seems justifiable that this bacillus is an undoubted cause of the ham souring which occurs in the packing house; and the results thus far obtained indicate that it is an important, if not the only, factor concerned in ham souring.

Having established the etiological relation of the bacillus isolated from sour hams with ham souring, the next point to be considered was the manner in which this bacillus finds its way into the bodies of the hams.

PROBABLE METHOD BY WHICH HAM-SOURING BACILLUS ENTERS HAMS.

Regarding the question of the probable method by which the ham-souring bacillus enters hams, there were three possibilities to be taken into consideration:(1) That the bacillus is present in the flesh of hogs at the time of slaughter,(2) that the bacillus gains entrance through the pickling fluids,(3) that the bacillus is introduced into the bodies of the hams in the handling or manipulation which the hams undergo in preparation for, or during, the process of curing.

Possibility of Infection Prior to Slaughter.

In order to throw some light upon this point, a number of fresh hams—that is, hams which had been chilled but not pumped or subjected to any other manipulation—were examined bacteriologically, but in no case could the anaerobic bacillus which was isolated from sour hams be detected in any of them. The fact that in certain of the smaller packing establishments which cure their hams without pumping the percentage of souring is extremely low would also seem to negative this possibility, for if the bacillus which causes souring were present in the hams at the time of slaughter, sour hams would be as frequent at such establishments as at those establishments which make a practice of pumping. Furthermore, a laboratory study, biological and chemical, of the bacillus isolated from sour hams shows that this organism belongs to the class of putrefactive bacteria, and while such bacteria may be present in the intestines of healthy animals, as, for example, the bacillus of Bienstock (Bacillus putrificus), these bacteria do not invade the organs and tissues of the body until after the death of the animal, and the packing-house practice of rapidly eviscerating the hogs immediately after slaughter would certainly preclude this possibility.

Possible Infection from Pickling Fluids.

With regard to the second possibility, that the bacillus finds its way into the hams in the curing pickles, it was determined by laboratory experiment that the addition of 3 per cent of sodium chlorid or 3 per cent of potassium nitrate to laboratory media completely inhibits the growth of the bacillus. As the pickling solutions always contain considerably more than these percentages of sodium chlorid and potassium nitrate, it would be impossible for the bacillus to multiply in the pickles. Additional laboratory experiments demonstrated, however, that the bacillus or its spores may remain alive in the curing pickles for at least thirty days, and it seemed possible that the curing pickles might become contaminated at times with the bacilli, and that the bacilli, although incapable of multiplying in the pickles, might find their way into the bodies of the hams in the pickling fluids. In order to throw some light upon this point, the following experiment was carried out:

EXPERIMENT TO SHOW WHETHER INFECTION TAKES PLACE FROM THE CURING PICKLE.

In this experiment two tierces were put down, each containing 20 hams. The hams weighed from 14 to 16 pounds and had received the usual 48-hour chilling. The pickling solutions employed were the regular curing pickles of the establishment at which the experiment was carried out. The curing pickle in one tierce was inoculated with 400 cubic centimeters of a culture suspension of the bacillus, prepared in the same manner as that used for the injection of the hams in tierce 2 in Experiment II. A microscopic preparation made from a small drop of the culture suspension before adding it to the pickle showed the bacilli in large numbers, and in the 400 cubic centimeters of the suspension there were millions of the bacteria. The curing pickle in the other tierce was left untreated, the hams in this tierce serving as a check. The tierces used in this experiment, as in all of the experiments, were thoroughly cleaned with boiling water before the hams were placed in them. The experiment was conducted in a pickling room which was held at 33° to 36° F., and the tierces were rolled three times during the cure. The details of the experiment are as follows: