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.
While tomato ketchup is a complex and variable product, its general composition may be determined with a fair degree of accuracy. Inspection will give a good idea of color, consistency, smoothness of body, fineness of finish, tendency to separate, presence of objectionable particles, and evidence of gross fermentation. The odor and taste will give a clue to the kind and quantity of spices used and to a certain extent the character of the raw material. Judging by odor and taste is not so well done as judging by the eye by most persons. The education of those two senses has been neglected and therefore fail to give all the information which might be acquired in this way.
A chemical examination which will give the specific gravity, total and soluble solids, sugar, salt, and total and volatile acidity, will be sufficient to give a good idea of the stock used—tomato, salt, sugar, and vinegar, but not the spices. A microscopic examination will assist in determining the condition of the material used and whether decomposition has taken place before or after manufacture. The facts obtained through these sources will permit of classifying commercial ketchup with a fair degree of accuracy.