Part 10

POSSIBLE INFECTION THROUGH MANIPULATION OR HANDLING.

There are at least three possible ways in which hams may become infected from the handling which they receive in preparation for, or during the process of curing, viz: From the thermometers used in taking the inside temperatures of the hams, from the pumping needles, and from the billhooks used in lifting the hams.

INFECTION FROM HAM THERMOMETERS.

The packing-house method of taking the temperatures of hams by means of a pointed, metal-capped thermometer which is thrust deep into the bodies of the hams has already been referred to, but deserves to be described somewhat more in detail, as it will be at once apparent that this manipulation furnishes a ready means whereby hams may become infected with putrefactive bacteria. The construction of a ham thermometer is shown in figure 4.

FIG. 4.—Diagrammatic views showing construction of ham thermometer. A, front view, showing open space between metal point and mercury bulb, which becomes filled with particles of meat, grease, and dirt; B, side view.]

The instrument consists of a glass thermometer inclosed in a metal case, the front portions of the case being cut away so as to expose the scale above and the mercury bulb below. As was explained before, the thermometer is thrust deep into the body of the ham so that the pointed end containing the mercury bulb rests beside or a little behind the upper portion of the femur, the bone being used as a guide in introducing the thermometer.

Ham temperatures are taken at three stages in the preparation for cure—(1) on the hanging floor, just before the hams go to the chill rooms, in order to determine the amount of heat lost prior to chilling; (2) on leaving the chill rooms, in order to determine the thoroughness of the chill; (3) on the packing floor, just before the hams are placed in pickle, as a further check on the thoroughness of the chilling.

In taking the temperatures of hams which have been chilled—and most of the temperatures are taken subsequent to chilling—it is customary for the packing-house attendant who has this matter in charge to warm the thermometer by holding the pointed or bulb end in his hand, so as to force the mercury column up to about 60° F., or well above the temperature of hams. The thermometer is then thrust into the ham and allowed to remain for several minutes, by which time the mercury column will have fallen to the temperature of the ham. The thermometer is then slowly withdrawn so as to expose the top of the mercury column, and an accurate reading is thus obtained of the inside temperature of the ham. The thermometer is warmed by the hand before each ham is tested, and this undoubtedly insures more accurate readings than would result were the thermometer removed from one ham and plunged immediately into another, but the procedure is open to certain objections, for the open space between the metal point of the thermometer and the mercury bulb soon becomes filled with particles of meat and with grease and dirt from the attendant’s hands, and it is at once apparent that a thermometer in this condition would furnish a ready means whereby extraneous matter might be introduced into the bodies of the hams. In other words, a contaminated thermometer would furnish an excellent means whereby hams could be inoculated with putrefactive bacteria.

In order to determine whether hams actually become inoculated in this manner, the following experiment was carried out:

EXPERIMENT TO SHOW WHETHER HAMS BECOME INFECTED FROM HAM THERMOMETERS.

This experiment was designed to show (1) whether the usual packing-house method of taking ham temperatures was apt to induce souring in the hams thus tested, and (2) whether souring would result in hams which were tested with a thermometer purposely contaminated with the bacillus isolated from sour hams.

The experiment was carried out as follows: Thirty hog carcasses were selected as they entered the hanging floor from the killing floor. They had been cleaned, eviscerated, and split, and were of the same average weight and of sufficient size to yield hams weighing from 12 to 14 pounds. They were divided into three lots of 10 each and were allowed to remain on the hanging floor for two hours, after which they were given the usual 48-hour chilling.

Lot 1.—The hams in this lot were tested with an ordinary ham thermometer as they entered the hanging floor, as they left the hanging floor, and as they left the coolers. The thermometer used was borrowed from one of the plant attendants and was used in the condition in which it was received from him; that is, it was not cleaned or disinfected prior to use.

Lot 2.—The hams in this lot were tested as they entered the hanging floor with a thermometer which had been previously cleaned and disinfected and then dipped in a culture suspension of the meat-souring bacillus which was isolated from sour hams. The thermometer was dipped in the culture suspension before each ham was tested. No further temperatures were taken of these hams. The thermometer was carefully cleaned and disinfected before it was returned to the attendant from whom it was borrowed.

Lot 3.—The hams in this lot were not tested at all, and were intended as checks on the cure.

The three lots of carcasses were carefully tagged and were chilled in a special cooler to themselves. Upon leaving the cooler the hams were cut from the carcasses and trimmed. The three lots of hams were then cured in separate tierces. All of the hams were subjected to exactly the same cure.

The pickles used were the regular pumping and regular curing pickles of the establishment at which the experiment was carried out.

The hams in lot 3 were pumped first and those in lot 1 were pumped next. The needle was then removed and a fresh, clean needle was used for lot 2. This was done in order to prevent the possibility of carrying over bacteria from one lot of hams to another on the pumping needle. The tierces were thoroughly cleaned with boiling water before being used. The curing was carried out in a pickling cellar which was held at 33° to 36° F., the temperature never rising above the latter figure. The tierces were rolled three times during the curing. The details and results were as follows:

Tierce 1.—Contained 20 hams, half of which were pumped in both body and shank and half in the shank only. These hams were taken from the carcasses in lot 1 and had been tested several times with a ham thermometer, as already described.

Result: At the end of the cure it was found that of the 10 hams which were pumped in the shank, 5 showed well-marked souring in the body, while of the 10 hams which were pumped in both body and shank, 2 showed slight souring in the body.

Tierce 2.—Contained 20 hams, which were pumped in the same manner as those in tierce 1. These hams were taken from the carcasses in lot 2 and had been tested once with a thermometer which was dipped in a culture suspension of the bacillus isolated from sour hams.

Result: The 10 hams which were pumped in the shank only all became sour. When they were tried out at the end of the cure, they showed pronounced souring throughout the entire body and were classed as “stinkers” by the meat inspector who examined them. The souring extended through to the bone marrow of the femur in all of these hams. Of the 10 hams which were pumped in both body and shank, 7 showed well-marked souring in the body, but not as pronounced as in those pumped in the shank only; in five of these hams the souring extended through to the bone marrow of the femur, while in 2 the bone marrow remained sweet.

Tierce 3.—Contained 20 hams, which were pumped in the same manner as those in the two preceding tierces. These hams were not tested with a thermometer, and were put down as a check on the cure. They were pumped with the same pumping pickle, subjected to the same cure, and held under precisely the same conditions as the hams in the two preceding tierces.

Result: When tested at the end of the cure, all of these hams were found to be perfectly sound and sweet.

Results of experiment to show whether hams become infected from ham thermometers. ────────┬────────┬───────────┬──────────────┐ │ │ │ │ │ │ │ │ No. of │ Number │ Average │ How pumped. │ tierce.│ of │ weight of │ │ │ hams. │ hams. │ │ ────────┼────────┼───────────┼──────────────┤ │ │ Pounds. │ │ │ │ │ │ │ │ │{ 10 in shank │ │ │ │{ │ 1 │ 20 │ 12-14 │{ │ │ │ │{ │ │ │ │{ │ │ │ │{ │ │ │ │{ │ │ │ │{ 10 in body │ │ │ │{ and shank │ │ │ │ │ │ │ │{ 10 in shank │ 2 │ 20 │ 12-14 │{ │ │ │ │{ │ │ │ │{ │ │ │ │{ │ │ │ │{ │ │ │ │{ 10 in body │ │ │ │{ and shank │ │ │ │ │ │ │ │{ 10 in shank │ 3 │ 20 │ 12-14 │{ │ │ │ │{ 10 in body │ │ │ │{ and shank │ ────────┴────────┴───────────┴──────────────┘

────────┬─────────────────┬────────────────── │ │ Condition at │ │ end of cure. No. of │ ├───────┬────────── tierce.│ Treatment. │Number │Percentage │ │of sour│ of sour │ │ hams. │ hams. ────────┼─────────────────┼───────┼────────── │ │ │ │Tested at several│ 5 │ 50 │stages in │ │ 1 │preparation for │ │ │cure with ham │ │ │thermometer which│ │ │had not been │ │ │cleaned. │ │ │ do │ 2 │ 20 │ │ │ │ │ │ │Tested once with │ 10 │ 100 2 │ham thermometer │ │ │dipped in culture│ │ │suspension of │ │ │anaerobic │ │ │bacillus isolated│ │ │from sour hams. │ │ │ do │ 7 │ 70 │ │ │ │ │ │ 3 │Not tested with │ 0 │ 0 │thermometer. │ │ │ do │ 0 │ 0 ────────┴─────────────────┴───────┴──────────

Several hams from each tierce were examined bacteriologically. cultures being taken from the meat near the bone and from the bone marrow of the femur.

In the sour hams from tierce 1 cultures taken from the meat near the bone showed the same anaerobic bacillus noted in other sour hams (i.e., the same bacillus which caused souring in Experiments I and II), but these cultures were contaminated with other bacteria which were probably introduced on the thermometer along with the ham-souring bacillus. None of the contaminating bacteria were capable, however, of producing a sour-meat odor when grown on the egg-pork medium. Pure cultures of the ham-souring bacillus were obtained from the bone marrow of some of these hams, showing that this bacillus had penetrated through to the bone marrow while the other bacteria had not.