A bacteriological study of ham souring

by Charles Neil McBryde

PREVENTION OF HAM SOURING.

As it has been shown that souring in hams results from the growth of a bacterium which is introduced into the bodies of the hams in the various manipulations which the hams undergo, the only way to eliminate souring in hams, as they are cured in the larger packing establishments, would be to cure the hams under aseptic or sterile conditions, which would, of course, be a physical impossibility.

While it will probably be impossible, therefore, to eliminate souring entirely under the methods of ham curing which are at present employed in the larger packing establishments, much can undoubtedly be done toward reducing the percentage of sours. In the matter of taking ham temperatures, for instance, if the thermometers used were thoroughly cleaned and disinfected and the surfaces of the hams seared at the point where the thermometer is introduced, infection from this source could be entirely prevented; or it might be possible so to regulate the temperature of the chill rooms that the taking of ham temperatures could be discontinued.

The elimination of the souring that results from the introduction of foreign matter on the pumping needles could be effected in two ways only,(1) by not pumping the hams at all, or (2) by pumping them under sterile or aseptic conditions. As has been stated before, some of the smaller packing establishments cure their hams without pumping, and in these establishments the percentage of sours runs very low. When hams are cured without pumping, however, the period of curing has to be materially lengthened in order to give the curing pickles sufficient time to penetrate thoroughly, and this is what the larger plants wish to avoid because of the greater space and greater number of vats which would be necessitated. The object of pumping in the larger plants, where the number of hams handled daily runs into the thousands, is to hasten the cure and thus prevent the accumulation of a great number of hams at one time. It is doubtful, therefore, whether the larger packing houses could conveniently discontinue pumping.

To pump the hams under aseptic conditions would necessitate a technique far too elaborate for routine use in the packing house; in fact, anything like complete asepsis would be out of the question. Certain measures might be adopted, however, that would tend to prevent the possible introduction of ham-souring bacilli in the process of pumping. It would undoubtedly be safer, for instance, to boil the pumping pickle before use, and the chances of carrying in contaminated foreign matter on the pumping needles could be lessened by sterilizing the pumps and needles with boiling water and by frequently dipping the needles, while in use, in boiling water. If the hams were sprayed with clean water just prior to pumping, there would be less likelihood of carrying in foreign matter on the needles. The danger of introducing contaminated foreign matter on the needles might be further obviated by searing the surfaces of the hams at the points where the needles are introduced; but such a procedure would be hardly practicable in the larger packing houses, where the great number of hams cured necessitates rapid handling.

While the danger of possible contamination in pumping, through the introduction of contaminated foreign matter on the pumping needles, can not well be avoided, this danger is partly counterbalanced by the inhibitory action of the pumping pickle, which is strikingly shown in the experiments which have been described. In these experiments, 100 hams received large doses of the ham-souring bacillus, half of these hams being subjected to the mild cure and half to the regular cure, with the following result: In the case of the mild-cure hams, which were pumped in the shank only, the percentage of sours was practically 100 per cent, every ham with possibly one exception becoming sour; whereas in the regular-cure hams, which were pumped in both body and shank, only 58 per cent of the hams became sour. In other words, the additional pumping which the regular-cure hams received served to prevent souring in 42 per cent of these hams. In these experiments the number of bacteria introduced into the hams was very great, thousands and even millions of the bacilli being introduced into each ham, whereas in the routine of the packing house it is not likely that more than a few of the bacilli are ever introduced at one time on the thermometers and pumping needles. In view of these results it is safe to say that in the larger packing houses, where pumping seems to be necessary, the number of sours could be reduced fully 50 per cent if all hams were pumped in the body as well as in the shank.

At present the usual procedure is to pump all hams, both mild and regular cure, with the same pumping pickle, the mild-cure hams being pumped in the shank only and the regular-cure hams at two additional points in the body. The experiments quoted above show that the additional pumping which the regular-cure hams receive undoubtedly tends to prevent the development of souring in these hams, and this result is unquestionably due to the inhibitory action of the salts contained in the pumping pickle, as it was found by laboratory experiment that the addition of 3 per cent of sodium chlorid to culture media is sufficient to inhibit the growth of the ham-souring bacillus. The pumping pickles consist of strong brine solutions and always contain considerably more than 3 per cent of sodium chlorid. If, therefore, the pumping of regular-cure hams were made more thorough than at present, and all of the deeper portions of the ham were thoroughly saturated with the strong brine solution, souring could be largely eliminated, if not entirely prevented, in these hams, as an unfavorable medium or soil would thus be created in which the ham-souring bacillus could not develop. The ham-souring bacillus is able to develop within the bodies of the regular-cure hams because the pumping of these hams is not always thorough and there are certain areas in the inner or deeper portions of the hams in which the tissues are not thoroughly saturated with the pumping pickle.

Under the present methods of curing, the greater proportion of the sours occur among the partly pumped or mild-cure hams. These hams are pumped in the shank only, and the growth of the ham-souring bacillus within the bodies of these hams is not interfered with until the curing pickle has penetrated from the outside. As it requires several weeks for the curing pickle to penetrate thoroughly into the deeper portions of these hams, the bacillus is thus afforded a considerable interval in which to develop before it is exposed to the inhibitory action of the pickle. If these hams could be thoroughly pumped in the body at the beginning of the cure in the same manner as the regular-cure hams, the chief loss from ham souring would be eliminated. It would not do, however, to pump these hams in the body with the same pumping pickle used in the regular cure, as the meat would be rendered too salty and the mild flavor of the ham would be lost. There is undoubtedly a demand for mild-cure hams, otherwise they would not be on the market; and the question then arises how to pump these hams and still retain a mild cure. This might be accomplished by pumping these hams with their own curing pickle, which is usually a milder pickle than that employed in the regular cure, or an even milder pumping pickle might be used. If mild-cure hams were pumped in this way, the percentage of souring in these hams could undoubtedly be greatly diminished without materially affecting the flavor of the ham.

To recapitulate briefly, the prevention of ham souring is to be sought in two ways:(1) Through greater care in handling the hams and the adoption of precautionary measures to prevent the introduction of the ham-souring bacillus into the bodies of the hams, and (2) through more thorough pumping of the deeper or inner portions of the hams, so as to create an unfavorable soil or medium in which the ham-souring bacillus can not develop even if it should gain entrance into the bodies of the hams.

From what has been said it will be apparent that ham souring can probably never be entirely eliminated from the packing house under the present methods of curing, but the adoption of precautionary measures in testing and pumping hams, together with a more thorough pumping of all hams in ways similar to those suggested, would unquestionably reduce very materially the losses from this source.