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.
[Illustration: A. B.
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slowly withdrawn so as to expose the top of the mercury column, and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: