A bacteriological study of ham souring

by Charles Neil McBryde

In carrying out this experiment four tierces of hams were “put down” or “packed”—that is, placed in cure. Two of the tierces were given the fancy or mild cure and two the regular or stronger cure. The hams in two of the tierces, one mild and one regular cure, were injected with a culture suspension of the bacillus; the other two tierces were not injected with culture and were put down to serve as checks on the cure. Hams weighing from 12 to 14 pounds were used for the mild cure, while for the regular cure hams weighing from 14 to 16 pounds were used. This was in accordance with the general rule which prevails in packing houses, the lighter hams being subjected to the mild cure and the heavier hams to the regular cure. The only difference between the mild and the regular cure in this experiment lay in the pumping. The hams which were given the mild cure were pumped in the shank only, while those given the regular cure were pumped in the body as well as in the shank.

All of the hams had received the usual 48-hour chill. They were all pumped with the same pumping pickle and cured in the same curing pickle, and were in cure for the same length of time. The pumping and curing pickles used were the regular pumping and curing pickles of the establishment at which the experiment was carried out, and the hams were cured in accordance with the fancy and regular cures as practiced at this establishment.

The hams were packed in new tierces which had been thoroughly scalded with boiling water. The tierces were held in a curing room which was kept at an average temperature of from 34° to 36° F., the temperature occasionally going as high as 38° and 40° F., but never above 40° F. The hams were left in cure for about 70 days, which is a little longer than the usual cure. The tierces were rolled three times during the cure. At the end of the cure the hams in all four tierces were carefully tested by an expert meat inspector, who knew nothing of the treatment which the hams had received.

The hams in two of the tierces were inoculated with a culture suspension prepared as follows: Ten tubes of egg-pork medium, each tube containing approximately 10 cubic centimeters of the medium, were inoculated with the bacillus and held at room temperature (20° to 25° C.) for six days. The cultures were then filtered through sterile gauze into a large sterile flask; this was done in order to remove the particles of meat, which might otherwise have clogged the syringes used in inoculating the hams. In transferring the contents of the culture tubes to the filter the tubes were washed out with sterile physiological salt solution (0.6 per cent sodium chlorid), and the meat particles on the filter were afterwards washed with the salt solution, a sufficient quantity of the latter being used to bring the total volume of filtrate to 400 cubic centimeters. A microscopic preparation from the filtrate showed the organisms in large numbers, with an occasional rod showing a large terminal spore. This suspension was used for the injection of 40 hams, each ham being given 10 cubic centimeters, or the equivalent of 2.5 cubic centimeters of the original culture. The hams were injected with the culture suspension by means of a sterile syringe carrying a long 5-inch needle. The needle was thrust well into the body of the ham at a point near the upper end of the middle bone or femur, the latter being used as a guide in inserting the needle and the injection being made into the tissues just behind and a little to one side of the upper end of the femur.

The details of the experiment were as follows:

Tierce No. 1 (fancy cure).—This tierce contained 20 hams weighing from 12 to 14 pounds each. These hams were pumped in the shank only. Immediately after pumping they were injected with 10 cubic centimeters each of the liquid culture or suspension described above. After injection the hams were immediately packed in the tierce, which was then headed up, filled with the regular curing pickle, and placed in cure.

Result: When tested at the end of the cure all of the hams in this tierce save one were found to be sour. In 10 of them the souring was very marked throughout the body of the ham and extended into the shank as well. In six the souring was very marked in the body of the ham, but did not extend into the shank. In three there was slight but well-marked souring in the body of the ham with no souring in the shank, and one remained sweet. The probable explanation of the variation in the degree and the extent of the souring will be discussed later. The bone marrow of the femur or middle bone was tested in all of the hams and found to be sour in 18. In one of the hams which showed only slight souring in the body the souring did not extend through to the bone marrow, and in the ham which remained sweet the bone marrow was also sweet. The fact that one ham in this tierce remained sweet was in all likelihood due to an oversight in making the inoculations. In making the inoculations the hams were spread out in a row on a table by a packing-house assistant, who removed the hams as soon as they were inoculated and placed them in tierces; and it is more than probable that the assistant removed one of the hams before it was inoculated in the interval when the writer was busy filling the syringe for the next inoculation.

Tierce No. 2 (fancy cure).—This tierce contained 20 hams of the same average weight as the preceding. They were pumped in the shank only, but were not injected with culture, being put down to serve as checks on the hams in tierce No. 1. These hams, therefore, were subjected to exactly the same cure and were held under exactly the same conditions as those in tierce No. 1, the only difference being that the hams in this tierce were not injected with culture.

Result: When tested at the end of the cure all of the hams in this tierce were found to be perfectly sound and sweet, showing that the curing in this instance was properly carried out and that the souring of the hams in tierce No. 1 was undoubtedly due to the injections of culture which they received.

Tierce No. 3 (regular cure).—This tierce contained 20 hams weighing from 14 to 16 pounds each. These hams were pumped in the shank and also in the body. Immediately after pumping they were each injected in the same manner as those in tierce No. 1 with 10 cubic centimeters of culture. The hams were then packed in tierce and placed in cure.