The conditions found in the rotted sections and pieces of tomato can be distinguished in the poor ketchup and these factors, together with the large number of organisms present, serve for purposes of differentiation.
Tomato pulp furnishes a medium suitable for the development of many organisms, as it contains all of the necessary food elements. The raw pulp has an acidity of from 0.2 to 0.4 per cent usually, though there may be variation due to fermentation and other causes. On account of its mild acidity, it is especially suitable for the development of many yeasts and molds, and some forms of bacteria, consequently there is present a varied and abundant flora if the pulp be held for an appreciable time before using, or if it has been made from tomatoes not properly sorted and washed. Where the black rot occurs on tomatoes, the tissue is hardened like cork, and if not removed on the sorting belt, is broken into small pieces by the cyclone, and appears as black specks in the ketchup, these being readily perceived by the naked eye. The white rot forms soft spots, which, though not so prominent as the black, carry much more contamination, as, apart from the bacteria, yeasts, and molds present, they are often swarming with Protozoa. These are not ordinarily recognized in the ketchup, as a chemical or physical shock causes them to contract, assume a spherical shape, and become motionless. In this condition they resemble the immature conidia of some of the molds. Rarely only one organism predominates in pulp from rotted fruit, then the rot consisting of a nearly pure culture. In all cases of soft rot, there is much more contamination carried, as the organisms are small and a greater number present in a given area. Whenever the inner tissue of tomatoes is exposed, organisms develop rapidly, the forms varying with the locality and the conditions in the pulp. Some of these organisms may survive the treatment of the pulp when converted into ketchup, or the original organisms may be destroyed, and a different set gain access and develop, but in either event all the organisms alive or dead which were present at the period of manufacture are found in the ketchup. It has been noted that certain brands of ketchup have predominating organisms present which are practically constant from year to year.