A bacteriological study of ham souring

by Charles Neil McBryde

This experiment was essentially a repetition of Experiment I, but was carried out at a different packing establishment and under somewhat different conditions.

Two lots of hams were injected with a culture suspension of the bacillus at different stages of the cure, or rather at different stages in the preparation for cure, i. e.,(1) on the hanging floor, previous to chilling, and (2) after chilling and pumping and immediately before packing. Three tierces, each containing 20 hams, were put down. Two of the tierces contained the hams injected with culture, while the third tierce contained check hams which had not been treated with culture. Half of the hams in each tierce were pumped in the shank, while the other half were pumped in both body and shank. The same pumping and curing pickles were used for all three tierces, and were the regular pumping and regular curing pickles of the establishment at which the experiment was carried out. The hams used were all 14 to 16 pounds in weight and were subjected to the usual 48-hour chill with an additional chill of 48 hours after they were cut from the carcass. They were packed in tierces which had been thoroughly scrubbed and cleaned with boiling water. The tierces were held in a pickling room at a temperature of 33° to 36° F., the temperature never rising above 36° F., and were rolled three times during the curing period. The hams were in cure for about eighty days. At the end of the cure the hams were carefully tested by a trained meat inspector, who knew nothing of the treatment they had received.

The culture suspension was prepared from 20 tubes of egg-pork medium in the same manner as that used in Experiment I, the cultures being diluted with sufficient salt solution to give 400 cubic centimeters of suspension. The cultures from which the suspension was prepared had grown at room temperature for ten days. The suspension was examined microscopically and showed large numbers of the bacilli in the form of filaments or long chains, with many of the individual organisms showing large terminal spores. The hams were injected with the culture suspension in the same manner as those in Experiment I.

The details of the experiment were as follows:

Tierce No. 1.—Contained 20 hams, each ham being injected with 20 cubic centimeters of the suspension or the equivalent of 10 cubic centimeters of the original culture. The hams were injected while on the hanging floor, before they had been cut from the carcasses and previous to chilling. The carcasses were still quite warm—that is, had lost but little of their body heat when the injections were made. The carcasses, which had been carefully tagged, were then run into coolers and given the usual 48-hour chill, after which the hams were severed from the carcasses and given an additional 48-hour chill in accordance with the custom of the packing house at which the experiment was carried out. The hams were next pumped with regular pumping pickle, 10 being pumped in both body and shank and 10 in shank only. They were finally packed in a tierce, which was then headed up, filled with regular curing pickle, and placed in cure.

Result: When tested at the end of the cure it was found that the 10 hams which were pumped in the shank only were all sour. In each of them the souring extended throughout the entire ham, in the shank as well as in the body, and was very pronounced, so much so that they were characterized as “stinkers” by the meat inspector who assisted in testing them. The bone marrow of the femur or middle bone was sour in all of these hams. Of the 10 hams which were pumped in both body and shank 7 showed well-marked souring throughout the body, but the souring did not extend into the shank. The bone marrow of the femur was found to be sour in 6 of these hams, while in 1 the souring had not extended through to the bone marrow.

Tierce No. 2.—Contained 20 hams which were chilled and pumped in exactly the same manner as those in tierce No. 1. These hams were injected with culture after they had been chilled and pumped, or just before they were placed in cure. The hams in this tierce, therefore, were injected with culture four days later than those in tierce 1. The hams were injected with a bacterial suspension prepared in the same manner as that used for tierce 1, except that the egg-pork cultures from which the suspension was prepared were 7 days instead of 10 days old. Each ham was injected with 20 cubic centimeters of the suspension or the equivalent of 10 cubic centimeters of the original culture. The hams were injected in the same manner as those in tierce 1.

Result: When tested at the end of the cure, it was found that of the 10 hams which were pumped in the shank all were sour; in 8 of these the souring was very marked throughout the body of the ham and extended into the shank; in all of these hams the souring had extended through to the bone marrow of the middle bone or femur. Of the 10 hams which were pumped in both body and shank 6 were sour in the body. These hams were classed by the meat inspector who examined them as “light body sours,” and in none of them did the souring extend into the shank or through the bone into the bone marrow of the femur.

Tierce No. 3.—Contained 20 hams which were chilled and pumped in the same manner as those in the two preceding tierces. These hams were not injected with culture and were put down to serve as checks on the cure. In other words, they were pumped with the same pickling fluids, were subjected to exactly the same cure, and were held under precisely the same conditions as those in the preceding tierces, 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.