The evaluation procedures that are used in the evaluation of subsistence items are the closed-package inspection and the open-package inspection.
a. Closed Package. The term closed package means an inspection of the product's packaging and packing materials, for evidence of a deteriorative condition. The integrity of the food package is not altered during this inspection. After the closed-package inspection, the sample unit can usually be returned to the lot from which it was drawn.
b. Open Package. The term open package means an evaluation of a food component for evidence of a deteriorative condition. The inner packaging material (opening the can or cutting the flexible packaging material) is destroyed during the inspection. After inspection, the product usually cannot be returned to its lot since the product or the packaging has been destroyed. Generally, open-package inspection is performed only on products which have been stored longer than is recommended. However, inspections may be made when storage conditions are extremely unfavorable, when isolated lots are inspected, when the inspector suspects internal deterioration, or when he has other important reasons for opening the packages.
(1) Evaluation of vacuum. Prior to opening of the container, an evaluation of vacuum, if applicable, must be made. When the food is processed in a jar or a can, a good vacuum inside the container is desired. A vacuum reduces the strain on the container during heat processing, holds the ends in a collapsed concave position during subsequent storage, and reduces the amount of headspace oxygen. The vacuum is obtained by exhausting with steam or by vacuum sealing. The loss of vacuum (springer formation) is one of the principle types of pack failure. The evolution of gas within the container causes the can ends to become distorted beyond the normal concave position. Gas may be formed either from hydrogen produced by corrosion on the inside of the can by the food product or by microbial action on the food product.
(2) Evaluation of food component. After determining the vacuum, evaluation of the food component is made. Practically all deteriorative conditions affecting the food component manifest themselves as changes from the normal characteristics or attributes of the product, such as a change of color, texture, odor, and/or flavor. These changes may be very pronounced or, at times, they may be very subtle.
(3) Evaluation of internal packaging. In addition to an evaluation of the vacuum and an evaluation of the food component, an evaluation of the internal packaging components must be made. The internal inspection may reveal defects not seen otherwise or may reveal the cause of defects observed during external inspection of the container. Examples of internal defects seen in cans are spangling, detinning, scarred or flaked enamel, pinholing, and flat sour.
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