The theories as to the cause of souring are many and varied. The
majority of them are pure speculation and have no foundation upon
observed facts. A few of these theories may be enumerated to show how
wide and varied has been the speculation upon this subject.
A theory which is quite prevalent among packing-house employees
attributes souring to overheating of the animal previous to slaughter,
but tests were made by driving hogs to the point of exhaustion just
prior to slaughter and curing the hams from these animals in comparison
with hams taken from animals which had been rested prior to slaughter,
with no difference in the cured product; that is, the hams taken from
overheated hogs cured equally as well as those taken from rested hogs.
Another theory attributes souring to a diseased condition of the meat.
Prior to the enforcement of the Federal regulations governing meat
inspection there might have been some ground for such a supposition,
but this theory could not hold at the present time, in view of the
thorough and efficient inspection now in force, for it can be safely
said that no diseased meat now passes the Government inspectors, and
therefore no diseased meat goes into cure in inspected houses. In
order to test this theory, however, hams were secured from a number
of condemned animals which showed various diseased conditions, such
as hog cholera, pyemia, septicemia, scirrhous chord, etc., and these
hams were cured in comparison with hams taken from normal hogs. It was
found that the hams taken from the diseased hogs cured equally as well
as those taken from healthy hogs. The hams from the diseased hogs were
destroyed after the experiment, as the meat taken from diseased animals
was of course not considered fit for consumption, the object of the
experiment being merely to determine whether or not souring is caused
by diseased conditions.
Another theory attributes souring to imperfect or too rapid chilling
of the meat before it is put in pickle, and places the blame upon the
refrigeration. According to this theory, souring results when the meat
is chilled too suddenly, the idea being that by the rapid congealing of
the juices of the meat a coating is formed on the outside of the ham
whereby the animal heat is prevented from escaping from the interior,
leaving the meat next to the bone at a higher temperature than the
outside of the ham.
In order to test this last theory, a number of hog carcasses were run
direct from the killing floor to a cooler at 28° F. and a like number
of carcasses of the same average weight which had been allowed to stand
for two hours at the outside temperature of the air (53° F.) were
placed in the same cooler. The carcasses which had hung for two hours
in the air had lost an average of 14 degrees in temperature before
going to the cooler. The temperature of the cooler rose to 29° F. after
the carcasses were put in, but was soon reduced to 28° F. and held at
this temperature. The temperatures of the hams were taken at the end
of 24 hours, and practically no difference was found in the inside
temperatures of the two lots; that is, the hams on the hot carcasses
which were subjected to a sudden chilling exhibited practically the
same inside temperature (i. e., next to the bone) as those which had
cooled for two hours at the temperature of the air before being placed
in the cooler.
Still another theory attributes souring to lack of penetration of the
pickling fluids, but analyses of sour and sound hams do not seem to
bear out this theory. The rate of penetration of the pickling fluids,
however, would seem to have some bearing on the subject, and this point
will be discussed later in connection with some laboratory experiments
on the inhibitory effects of sodium chlorid and potassium nitrate.
So much for the more commonly accepted theories which have been
advanced to explain ham souring.