INTRODUCTION TO FOOD CONTAINERS
a. Canning. For a number of years now, perishable foods have been preserved
in metal or glass containers using a thermal process (heat treatment) to achieve
commercial sterility, which leaves the food product free of viable microorganisms.
These containers are hermetically sealed; that is, they have an airtight seal designed to
secure against the entry of microorganisms. Canning may be defined as the
preservation of perishable foods in containers, to include a hermetic seal, after having
been subjected to a heat treatment adequate to destroy those organisms hazardous to
b. Necessary Knowledge. The veterinary food inspection specialist must be
familiar with various aspects of the can manufacturing process in order to understand
the terms and concepts involved. This knowledge will be needed when cans are
inspected for defects. In addition, some familiarity with glass containers, "tray pack"
cans, and retort pouches will be needed.
Cans are made on a series of machines collectively known as a can line. This is
a continuous process from the entrance of the sheets of tin plate at one end of the can
line to the emergence of the completed and tested can at the opposite end. Veterinary
food inspection specialists must have a general knowledge of this process to
understand can defects.
a. Steel Base Plate. The steel base plate is the sheet of steel that forms the
base for the fabrication of metal containers. It is usually 0.01 inch thick. Specifications
require that cans will be made from plates having a base box weight of not less than
that in common commercial use for the specific product, style, and size of can. (The
base box is a merchandising unit used for transactions in the tin plate industry. The unit
consists of 112 sheets of tin plate, the dimensions of which are 14 by 20 inches.)
b. Tin-Plating. Tin-plating is a process by which a thin film of pure tin is
deposited over both sides of the steel base plate. (See Figure 1-1). A 1.0-pound tin
plate has a film of tin 0.000065 inch in thickness and contains as many as 8,000 pores
per square centimeter. Therefore, it can be seen that the film of tin on a tin can is not
impervious; that is, it does not prevent the content of the can from penetrating through
to the steel. The presence of these pores requires the application of enamels and
coatings to further protect the cans and the product. As a matter of information, pure tin