There is included in the bulletin beginning on [page 13] a detailed description of the Howard method for the microscopic examination of tomato products, and following that a detailed statement of the chemical and physical methods employed in this laboratory for their examination. Such methods are only of value to those trained in laboratory work. They are included here because the laboratory receives many requests for these methods from chemists employed by manufacturers of pulp. Men who are employed only for the tomato season find special need for such information.
Our correspondence brings many inquiries regarding the percentage of solids in pulp of different specific gravities, and also regarding the relative values of pulp of different specific gravities. In [Table 10] ([p. 59]) there is given in parallel columns the specific gravities of pulp of different degrees of concentration and corresponding percentage of solids, and it is a simple matter to calculate the volume which the same pulp would make if concentrated to any other specific gravity. This calculation is explained on [page 54]—in discussing the point at which to stop evaporation to secure pulp of any desired specific gravity.
This bulletin supersedes Bulletins 3 and 7, and also contains material which has appeared in several trade-paper articles prepared in this laboratory. These articles are extensively quoted and some of them are printed almost in full. Dr. F. F. Fitzgerald was the co-author of most of these publications and did much of the work on which they were based. He is therefore entitled to a substantial share of the credit for the material in this bulletin.
SANITARY CONTROL OF TOMATO PULP FACTORIES
The manufacture of tomato pulp requires careful supervision from beginning to end. The raw product must be carefully selected, and all possible steps should be taken to induce growers to discard rotting tomatoes in the field and to expedite the movement of the raw product from field to factory. Tomatoes must be carefully washed and sorted. It is only practicable to accomplish the latter by means of some type of sorting belt. Sorters should not attempt to trim. Their full attention should be given to the tomatoes passing by them. The sorter may place the tomatoes requiring trimming in a separate receptacle in order that they may be carried to a table not provided with a moving belt and handled by special trimmers. Conveyors, receptacles and machines must be constructed and installed with a view to convenience in cleaning. Care must be taken to expedite the manufacture of the product in every way possible in order to give no opportunity for bacterial growth during the process of manufacture.
The brief comments given above are offered by way of reminder. This important subject is not further discussed because it has been adequately treated by Mr. B. J. Howard of the U. S. Bureau of Chemistry in bulletins which are readily available. These bulletins are designated as Bulletins 569 and 581, respectively, of the United States Department of Agriculture. They may be secured by requesting them of the Superintendent of Documents, Government Printing Office, this city, and enclosing five cents in coin for each copy desired. All manufacturers of tomato pulp will do well to study these bulletins and have them studied by their responsible employees.
QUALITY OF PRODUCT
There is a growing tendency to give increased attention to the quality of tomato pulp. The tomatoes should be ripe and well colored. Green tomatoes or tomatoes with green portions not only do not have the requisite amount of red coloring matter but they contain material which masks and dulls the color of fully ripe tomatoes. There is a difference of opinion among successful manufacturers of pulp regarding the relative color of pulp manufactured after hot or cold cycloning. Some maintain that a better color is obtained by cycloning hot. Others, apparently equally skilled and able to manufacture an equally good product, maintain the reverse. Much depends on the control of the cyclone—the setting of the paddles and the speed at which they are operated.
The evaporation should be as rapid as possible. The operation of the kettles in such a way that the pulp burns on the kettles or on the coils damages the flavor of the product and impairs its color. The pulp should be cooled promptly after processing, or if that is not practicable should be stacked loosely so that the cans will have ample ventilation until they are entirely cooled.
Pulp packed in five-gallon cans is rarely processed. It should, however, be filled into the cans at a temperature of at least 180° F. It is best to give pulp in No. 10 and smaller size cans a short process in boiling water. With pulp filled at 180° F., ten or fifteen minutes is a sufficient cook. Pulp filled at lower temperatures or which is allowed to partially cool before processing requires a longer process.