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.
From the sour hams in tierce 2 the ham-souring bacillus was recovered
readily, and often in pure culture, from the hams which had been pumped
in the shank only, whereas it was usually contaminated with pickle
bacteria in the hams which had been pumped in both body and shank.
In the case of the sound hams in tierce 3, cultures taken from the meat
near the bone and from the bone marrow of the femur were negative in
the hams which had been pumped in the shank only, while cultures taken
from corresponding points in the hams pumped in both body and shank
showed ordinary pickle bacteria, which had evidently been introduced
into the bodies of these hams in the pumping pickles. None of these
hams exhibited the slightest sour odor.
_Summary of experiment._—In this experiment 20 hams (tierce 1) were
tested with an ordinary ham thermometer in the usual packing-house
manner. Half of these hams were subjected to the mild cure and half
were given the regular cure, with the result that 50 per cent of those
receiving the mild cure and 20 per cent of those receiving the regular
cure became sour.
A second lot of 20 hams (tierce 2) were tested with a thermometer
which had been purposely contaminated with a culture suspension of the
ham-souring bacillus. These hams were cured in the same manner as the
first lot, with the result that all of those receiving the mild cure
and 70 per cent of those receiving the regular cure became sour.
A third lot of 20 hams (tierce 3) which had not been tested at all were
cured in the same manner as the two preceding lots, as a check on the
cure. All of these hams were sweet at the end of the cure.
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.