Ketchup must not only keep while in the unopened bottle, but for a
reasonable time after opening, if it is to be a commercial success.
Every canner understands that if he puts food in a hermetically sealed
package and sterilizes by heat, that it will keep until opened. The same
principle applies to ketchup in the bottle, but there are some packers
who wish to be spared this expense and trouble and prefer to use a
substitute for heating.
The keeping quality after opening depends upon the utilization of the
same principles followed in the household operation of making fruit
butters, ketchup, preserves, and pickles, that is, sufficient
concentration and the use of sugar and vinegar. A ketchup can be made
essentially a pickle with an excessive quantity of vinegar and it will
keep; it can be made a preserve with excess of sugar and it will keep;
or, it can be made a distinctive sauce well concentrated in which the
vinegar and sugar are used only in sufficient quantity to give proper
flavor, and it will keep. Apple juice or cider will spoil quickly if
allowed to stand in a warm place; apple sauce will behave in like manner
only a little more slowly; but if the juice and sauces be boiled
together until they have acquired the consistency or state known as
apple butter, they will keep very well. The acidity, sugars, and solids
have been increased by the concentration. In the making of tomato
ketchup, the fruit does not have sufficient acidity and sugar of itself
to give preservative property at the concentration desired for a sauce,
so these are augmented by the addition of vinegar and sugar.
A great deal of stress has also been placed upon the effect of the
spices in acting as preservatives. Experiments have demonstrated
conclusively that when these are used in the small quantities required
for flavoring, that their effect is practically nil. The active
principles of the spices are effective only when present in the
proportion of 1 to 500 or 600 and in ketchup the proportion is only 1 to
several thousand. Likewise the quantity of salt is too small to have
effect.
The keeping qualities of a mild ketchup will depend far more upon the
sterilization than most manufacturers realize. It is easy to make almost
any ketchup apparently keep while the bottle is unopened. The spoilage
after opening is most often observed to be due to mold which has been
assumed to come from infection from the air. As a matter of fact, this
is nearly always due to spores which have been held in abeyance, due to
lack of air while in the bottle, and which begin growth as soon as
conditions are favorable. Spores which fall into the bottle from the air
might be unable to germinate upon such a medium, while those already
present would.