In ketchup manufacturing it is customary, if an agitator is not used,
to put a small amount of fat in the kettle to check the ebullition
during the reduction of the pulp. The amount used in this manner is not
sufficient, however, to be apparent in the ketchup. Brannt[D] states
that in some factories, where the trimmings are allowed to accumulate
for the season, they are given liberal doses of oils and condiments
when cooked, in order to disguise their defects, so that the product
can be placed on the market as “fresh tomato catchup.” That the use of
oils is increasing is evident from the comparison of the ketchup of the
past season with that of former years.
[D] Brannt, W. L., A Practical Treatise on the Manufacture of Vinegar,
1900, p. 455.
When oil is used in ketchup, it is easily detected under the
microscope, as it appears in the form of shining, yellow globules which
blacken gradually when treated with osmic acid. Besides this, the oil
comes to the surface of the ketchup, where it can be seen readily, and
if considerable oil has been used a distinct layer is formed. When
the ketchup has been made for some time, the oil changes so that the
ketchup has a peculiar “greasy” odor, or the oil may be so changed as
to give a decidedly rancid smell to the ketchup. Oil usually causes a
deterioration in flavor and odor, though some of the ketchups to which
it has been added do not spoil readily. Olive oil, cottonseed oil,
and oleomargarine are used. That the oil is not considered one of the
regular known ingredients of the ketchup is shown by the failure to
declare its presence on the label.
To test the antiseptic value of oils in ketchup, experiments were
made, using olive oil, cottonseed oil, and oleomargarine in the
proportions of 1 part of oil to 1,000, 750, and 500 parts of ketchup,
respectively. The ketchup was made in small quantities, 2 gallons
for each experiment. After bottling, all except the check bottles
were inoculated with Penicillium and kept at kitchen temperature. All
spoiled, and neither the quantity nor kind of oil used had any marked
effect in preventing spoilage. That the oils affected the development
of the mold was evident. The mold developed first at the junction of
the ketchup with the bottle forming a ring which spread gradually over
the surface developing a somewhat heavy mycelium. This remained white
longer than usual, spores forming very gradually, as indicated by the
change in color from white to a delicate blue. At the end of three
weeks only spots of color appeared on the surface and these were still
blue, though in ordinary development the blue color changes to green in
two or three days.
Another test was made, using olive oil only, and in the proportions of
1 part of oil to 500, 400, and 300 parts, respectively, of the ketchup.
Reduction was made in a steam-jacketed kettle, the oil being added
when the ebullition of the ketchup was the strongest, after which the
boiling was continued for fifteen minutes. The ketchup was bottled,
unsterilized bottles being used, then covered loosely with the metal
caps.
The time required for the ketchup to spoil was longer than in the first
set, but there was not sufficient difference nor enough uniformity in
the time to indicate that the use of oil in ketchup is desirable, even
if the change of flavor and odor be not taken into consideration. The
average number of days before spoilage for those containing 1 part of
oil to 500 parts of ketchup, was thirteen and two-thirds days; one
has not yet spoiled (a period of forty-five days), while the first
bottle spoiled in four days. Those having 1 part of oil to 400 parts
of ketchup had an average life of nine and three-fourths days, the
minimum being three days, and the maximum twenty-six days. Those having
1 part to 300 parts of ketchup on an average did not spoil for six and
three-fourths days, the minimum being four days, and the maximum eleven
days.
The failure of some of the bottles to spoil, though similar in every
known respect to those which did spoil, is a feature peculiar to
ketchup and is familiar to manufacturers who make careful tests before
putting their product on the market. For this reason a rather large
number of bottles should be used in a test in order that the results
may be approximately accurate and represent general conditions.