Microscopic Examination

The laboratory of the National Canners’ Association is frequently asked to examine samples of tomato products to determine whether or not they comply with the Government requirements. In examining these samples we use the Government method (the Howard method), but do not participate in the discussions regarding its merits and shortcomings.

It is our experience that skilled analysts can check themselves and each other with reasonable accuracy, and it is our duty to tell the manufacturer whether his product is legal. Should the Bureau of Chemistry adopt some other method as preferable to the Howard method, it would be our duty to use the new method and continue to serve the industry by telling the manufacturer whether samples submitted by him would pass the Government tests.

With a full understanding of our attitude in this matter many manufacturers of tomato products send samples from time to time for examination. It is made plain in every instance that the results obtained by the examination of a particular sample refer only to the batch from which that sample was taken and may give no indication of the character of any other batch.

Some manufacturers of tomato products use the Howard method as a check on their factory control. For this purpose it is not satisfactory to have samples examined in a laboratory located at a distance from the factory. Even if several samples are examined from a day’s run, they probably do not represent all the pulp manufactured on that day. It sometimes happens that one wagonload of tomatoes is almost entirely free of rotting material, whereas the succeeding load contains a considerable amount. Even with inefficient sorting, the pulp made from the first load will show a low microscopic count whereas, unless sorting is exceptionally good, the pulp made from the second load may show a high count. Thus one batch may readily comply with the requirements of the Bureau of Chemistry and the next batch may be outside of those limits. Because of this fact this laboratory recommends that manufacturers of tomato pulp do not rely upon the microscopic results of a single sample. The only way in which the product may be absolutely controlled by means of the microscopic count is to examine a sample from each batch—that is, from each kettleful or tankful that is evaporated. This is manifestly impossible. It would require several analysts for one plant. Moreover, it is entirely unnecessary.

It has been found that much better results can be secured by having an analyst in the plant to examine samples from time to time. Then, whenever the microscopic count becomes excessive, he can locate the trouble and see that it is corrected.

Manufacturers who desire frequent analyses of their products, therefore, should employ an analyst and arrange to have him instructed in a laboratory conversant with the Howard method as used by the Government. The laboratory of the National Canners’ Association makes it a practice to give the necessary instruction in this method to analysts employed by members of the association. These analysts should be carefully selected. Other things being equal, better results should be expected of a college graduate or at least one who has had college training in biology and chemistry. It has been repeatedly demonstrated, however, that a carefully selected man or woman with common school education can learn the method and use it with sufficient accuracy for factory control. The person selected for this work should have good powers of observation and a positive character.

This laboratory has heretofore advised that manufacturers of tomato pulp should not give too much attention to the microscopic count of their product. We have maintained that the expense would be better placed on the sorting belt; that if the sorting and trimming were adequately done, the plant maintained in a sanitary condition and the product manufactured as rapidly as possible, a low microscopic count would be assured. This we still maintain is true. So many cases have come to our attention, however, in which canners have not succeeded in maintaining the degree of sorting necessary with a product of this kind that we have grown to feel that the presence of an analyst working continuously in a plant is an additional safeguard.

The conditions attending the canning of tomatoes are widely different from those attending the manufacture of tomato pulp. The ordinary rot is almost always apparent from the outside of the tomatoes[3] and is removed by the peelers when preparing tomatoes for canning. Practically none of it, therefore, finds its way into the can. With pulp it is quite different. Any rot which is not removed by sorting and trimming goes into the cyclone and passes into the pulp. With trimming stock pulp, the condition is obviously much worse than with whole tomato pulp. One hundred pounds of tomatoes will yield not far from 85 pounds of cyclone juice. If only trimming stock is made into pulp, however, nearly half the tomatoes are used for canning and the remainder (50 or 55 pounds of trimming stock) will only make something like 35 or 40 pounds of cyclone juice. Yet, since the rot is almost entirely on the outside of the tomatoes, this 35 or 40 pounds made from the trimming stock contains the same amount of molds as the 85 pounds manufactured from the whole tomatoes. The mold count of the trimming stock pulp, therefore, is much higher than that of whole tomato pulp made from the same raw product.

The Bureau of Chemistry condemns tomato pulp whose microscopic examination gives results as high as the following figures: