A bacteriological study of ham souring

by Charles Neil McBryde

Inasmuch as the three lots of hams were cured under precisely the same conditions and were handled in the same manner prior to pickling, the only difference being that the hams in tierces 1 and 2 were tested with the ham thermometer while those in tierce 3 were not, we must conclude that the souring of the hams in tierces 1 and 2 resulted from the testing which these hams received. In the case of tierce 1 the hams became infected from a thermometer which, in the ordinary routine use of the packing house, had become accidentally contaminated with the ham-souring bacillus. In the case of tierce 2 the hams became infected from a thermometer which had been artificially contaminated with the bacillus. The high percentage of sours in this last lot is due to the fact that these hams were heavily infected with the ham-souring bacillus, for owing to the construction of the ham thermometer many thousands of the bacilli were unquestionably introduced into each ham on the point of the thermometer. In the ordinary routine of ham testing, where hams become infected from foreign matter introduced on the thermometer, the percentage of souring, as shown in tierce 1, would be less, for it is not to be supposed that ham thermometers are always contaminated with the ham-souring bacillus, but that they only become so at times, and that probably only a few of the bacilli are then introduced.

This experiment, we think, proves conclusively (1) that the ham-souring bacillus may be introduced into the bodies of hams on the thermometers used in testing the hams, and (2) that the packing-house method of taking ham temperatures by means of a thermometer which is thrust deep into the bodies of the hams may cause souring in the hams thus tested.

As a further proof that hams may become contaminated in this manner, a series of cultures were made from scrapings taken from ham thermometers. The scrapings consisted of the accumulations of bits of meat, grease, and dirt that collect on the thermometers, and were taken from the thermometers while the latter were in ordinary routine use in the packing house. In a series of six cultures which were made from such scrapings at different times, the same bacillus which was isolated from sour hams and shown to cause meat souring was found three times. In other words, the ham-souring bacillus was present in 50 per cent of the cultures made from thermometer scrapings, and many hams undoubtedly become infected from the thermometers. Souring would be almost certain to result in mild-cure hams if these hams were tested with a thermometer which had become accidentally contaminated with the ham-souring bacillus, as the bacillus would have time to develop within the bodies of the hams before being inhibited by the curing pickle, which penetrates slowly into the bodies of these hams. In the case of regular cure hams—that is, hams which are pumped in both body and shank—souring would be much less apt to occur after the use of a contaminated thermometer, as these hams are more or less saturated with a strong pumping pickle at the beginning of the cure, which would tend to inhibit the growth of any bacteria that might be introduced on the thermometers.

The fact that souring may result in hams from the use of a contaminated thermometer would explain the occurrence of several sours in one vat, for in testing hams just before they go into cure several hams are usually tested in succession, and these would in all likelihood go into the same vat. Supposing the thermometer to have been contaminated with the ham-souring bacillus at the time these hams were tested, this would explain a fact which has been often noted, namely, the occurrence of several sours in one vat while other vats containing the same run of hams show no sours.

If souring resulted in all of the hams which are subjected to a thermometer test in the daily routine of the packing house, this manipulation alone might account for nearly all of the sours which occur, but the experiment which has been just described shows that all of these hams do not become sour. In tierce 1, where each ham was subjected to three thermometer tests at different times, souring resulted in 35 percent (this includes both mild and regular cure) of the hams thus tested, and in actual practice the percentage of sours in hams which have been subjected to the thermometer test would probably be somewhat less. Quite a large percentage of sour hams are thus left unaccounted for by the thermometer test, and we believe that these are chiefly the result of contamination carried in on the pumping needles or in the pumping pickles.

INFECTION FROM PUMPING NEEDLES.

In view of the results obtained in the last experiment, in which it was shown that hams may become infected from the use of ham thermometers, it seemed not improbable that hams might also become infected from the pumping needles, which, like the thermometers, are thrust deep into the bodies of the hams beside the bone. In order to throw some light upon this point, cultures were taken from the grease and dirt that accumulate on the shields at the bases of the pumping needles, as such material must undoubtedly be carried into the hams at times on the needles. The ham-souring bacillus was found several times in these cultures, and hence it is fair to infer that hams may also become infected at times from the pumping needles, just as they become infected from the thermometers. Bits of contaminated meat and grease and particles of dirt carried in on the pumping needles would be forced out into the hams by the pumping pickle, which passes out through small openings or fenestræ in the needles, and this probably affords one explanation as to why so many more body sours occur in the mild-cure hams. In the mild-cure hams, which are pumped in the shank only, the pumping needle is introduced near the femorotibial articulation, and the shank is saturated at the start with a strong brine solution, while the body of the ham is not. If the ham-souring bacillus were carried into these hams on the pumping needle, the growth of the bacillus in the shank would be inhibited by the strong brine solution with which the shank is saturated, but there would be nothing to prevent the bacillus from growing upward into the body of the ham, which has not been pumped and is free from pickle. This would also explain the fact that the souring often starts at the knee joint and extends upward into the body of the ham. In the case of the regular cure hams, where the ham is pumped in both body and shank, the entire ham is more or less saturated at the start with the strong brine of the pumping pickle, which tends to inhibit the growth of the ham-souring bacillus even if this bacillus should find its way into these hams on the pumping needles. It is in the mild-cure or partly pumped hams, where the body of the ham is left unpumped, that the ham-souring bacillus finds its best opportunity for development, and the greater proportion of the sours that occur in the packing house are found in these hams.

As regards the possibility of infection from the pumping pickle itself, it does not seem probable that this would often occur, for the pumping and curing pickles are always prepared on an upper floor of the pickling houses and are delivered to the pickle cellars in closed pipes, so the chances for the accidental contamination of these solutions from floating dust or dirt would not be great. Furthermore, the strong brine of the pumping pickle would completely inhibit the growth of the ham-souring bacillus, and the bacillus would be incapable of multiplying, even if it found its way into the pickle. On the other hand, laboratory experiments show that the bacillus or its spores may remain alive for a considerable length of time in the pumping pickle, so the possibility of infection from this source can not be overlooked.

INFECTION FROM BILLHOOKS.

After the hams are cut from the carcasses they are handled entirely by means of billhooks. In handling the hams the hooks are inserted beneath the skin of the shank at a point just above the tibio-femoral articulation. The hooks should be inserted in the connective tissue beneath the skin and should not penetrate the muscular tissue to any depth. When the hams lie in the right position, with the butt or large portion away from and the shank toward the operator, it is an easy matter to pick them up in the proper manner; but when they lie at different angles and are being rapidly handled it is almost impossible to prevent the hook from penetrating the muscular tissues, and if the hook should penetrate to the bone it might carry in foreign matter contaminated with the meat-souring bacillus. It is not probable that many hams become contaminated in this way, as the men who handle the hams are very skillful in manipulating their hooks; but the possibility that hams may become contaminated in this manner should not be entirely overlooked.