We will say that we have stacked away a 5–gal. can of pulp which contains several living spores of bacteria, as is apt to be the case, since the air is full of them, and the pulp is constantly open to contamination from the air after it is cooked; also the spores may be in the empty cans at the time they are filled. Why is it, since these few spores are alive, and in a favorable medium for their growth, that the rod-shaped bacteria forms which they produce do not multiply to such an extent that they will ferment the can of pulp. It was stated above that bacteria do not multiply in a strongly acid medium. Since the bacteria produce acid as a by-product of their own growth, they surround themselves with an acid medium, and they thus retard and finally stop their growth by the product of their own reproduction. When this acid medium reaches a certain strength the bacteria can no longer multiply, and if that can is not moved until used, the chances are it will be all right when opened. But if the can is moved, the contents are agitated, and these living bacteria are shaken away from the acid medium in which they have been suspended, and they are shaken into a fresh, sweet medium in which they can again begin to multiply. It may therefore follow that if this can is moved several times it would be at least partly fermented when opened, while if it was left alone it would have remained sweet. This illustration shows the desirability of moving pulp as little as possible, and as carefully as possible when moving becomes imperative. The lack of air in the can will, of course, also retard bacterial growth, but there is usually a small amount of air in the can, and many species of bacteria do not need any air whatever for their growth.
Fig. 7.—Mold spores and filaments. A type frequently found in decaying tomatoes. (×300.)
Rapidity of Growth
Yeasts and bacteria multiply more rapidly than do the molds, and that is why pulp which is made from tomatoes or tomato peelings which are handled slowly or carelessly usually shows a high content of yeasts and bacteria, while the molds may be low. As a rule, most of the mold found in pulp was present in the original tomatoes, and is found in the pulp because it wasn’t eliminated in the sorting. But, as a rule, tomatoes are not full of yeasts and bacteria unless they are very soft and mushy, and it is evident on looking at them that they have fermented to some extent. If pulp contains a high count of yeasts or bacteria it usually means that this fermentation took place in the factory at some stage in the manufacturing process, or that the product has been contaminated by fermented tomato substance lodged in pipes, troughs, and conveying equipment. Often it is due to delay in getting the tomato stock to a boil. The laxness in this regard in some factories is surprising, and their pulp is almost always high in yeasts and bacteria.
When you consider the extreme rapidity with which these germs multiply, the folly of allowing tomato peelings or tomato juice to be very slowly conveyed to a large tank for an hour or more before the steam is turned on becomes apparent. Much has been written about the rapidity of bacterial reproduction, and yet extreme delay in working up tomato stock continues in many plants, and we frequently see bacteria counts of a hundred million or more per cubic centimeter, all of which could be easily avoided if the packer would just make up his mind to get to the bottom of the cause and apply the simple remedy.
Just as an illustration we will say that we are putting up trimming pulp, and the tomato receipts are rather light and the peelers are working slowly, or that there aren’t many peelers working. The trimmings are passed along on a belt conveyor where they go to a bucket carrier and are lifted to a large cypress tank with a coil. They drop into the tank slowly, and it may take two hours for the coil to be covered so that the steam can be turned on; or after a foot or two of the trimmings have been put in the tank it is lunch time, and it is an hour before the filling of the tank continues. This may make it three hours before these peelings are brought to a boil. Suppose at the time those peelings go into the tank they contain enough bacteria so that if they were cooked at once, the pulp would run 10 million to the cubic centimeter. This is very probable. However, they are not cooked at once and at the end of 30 minutes you have peelings which, when condensed and cycloned, would show close to 20 million bacteria. In an hour the first peelings which entered that tank would yield 40 million, and in 1½ hrs., 80 million. This is on the basis of the bacteria reproducing themselves every 30 minutes. Even if they multiply much more slowly than that you can see that in the course of a little over an hour you are getting into dangerous ground, and in the course of two or three hours the bacteria have multiplied to such an extent that the product would almost be sure to be condemned if it was picked up by an inspector. If the tomatoes had quite a few soft spots in them when they were peeled it is very likely that the peelings would yield 20 million bacteria if worked up immediately, and then if delay of an hour or more comes on top of that you can see where you will be on the bacteria count. The yeasts are also probably multiplying at the same time, and the molds are growing to some extent.
Now what this packer should do is to put a small open steam jet in the bottom of his cypress tank, with four pipes running horizontally, as in a “breaking tank,” and turn on the steam as soon as the peelings cover these pipes, which lie right on the bottom of the tank. The peelings are thus kept at a boil until the steam can be turned on the coil, and then the steam from the open jet can be shut off. This is a very simple arrangement to make and will save no end of trouble.
It must not be thought that because micro-organisms multiply most rapidly in a warm medium they will not multiply in a cold medium, or one which is considerably warmer than blood heat—the degree of temperature most favored. The only safe extremes are 33 degrees F. for the lower extreme, and 150 degrees F. or above for the higher extreme. Anywhere between these two extremes of temperature there is danger of germ activity, and the nearer the medium is to 98 degrees F., the more rapid is the multiplication of the germs.
As tomato juice contains all the nutritive requirements for the growth of micro-organisms, and is not strongly acid, it is an ideal medium for them to grow in. There doesn’t seem to be any medium whatever that molds, yeasts, and bacteria prefer to tomatoes and tomato juice.