Guide to Inspections of Low Acid Canned Food 9
them. Too small a headspace in the container may result in a thermal process which is not adequate, and may also result in a low vacuum in metal containers producing flippers or springers. Too large a headspace results in excessive air in the container which may accelerate product and container deterioration and may also affect the net contents requirements of the container.
Gross headspace is defined as headspace (the distance from the top of the container flange or double seam for cans and top of the lip for glass containers to the top of the liquid in the container) or net headspace (the distance from the inside bottom of the lid or glass closure to the liquid in the container. A gross headspace of 1/4 inch in a metal container results in a net headspace considerably less than 1/4 inch due to the counter sink of the container lid.
Headspace is customarily measured in 1/32 of an inch. Measurement can be made by using a plastic or metal headspace gauge made specifically for that purpose or by placing a straight edge across the top of the container and extending a ruler down to the center of the container until it just touches the liquid.
Orientation - Orientation of the product in the container and/or the container in the retort may affect the thermal processing of lacfs. This is particularly true for products such as asparagus spears, leafy vegetables such as spinach, and other convection heating products in which the convection currents in the containers are affected by the orientation of the product in the container and hence container orientation in the retort. Processing of asparagus spears with the tips up may require several more minutes to achieve the same thermal process as processing the same spears tips down. The processing of large containers of spinach greens in the vertical position may require several more minutes to provide the same thermal process as when the containers are processed on their sides. If container and/or product orientation has been identified as a factor critical to the thermal process, there should be a method in place to insure that the critical factor is under control. During inspection of lacf manufacturers you may note the same containers of product being processed in different orientations in the retort. The firms processing authority should be able to determine if container orientation is critical to the process if there are any questions regarding product or container orientation.
Mechanical Vacuum - "Vacuum packed products" such as corn, sweet potatoes and crab meat are produced by adding a small amount of liquid to the container, adding the product to the container and creating a high vacuum in the container mechanically. Products packed in this manner are reported to be of superior quality. Mechanical vacuums of 23" to 27" are normally required at the closing machine and are filed as part of the thermal process. The container then becomes its own processing system as the liquid in the container turns into steam during thermal processing of the product. In addition to the required mechanical vacuum, the % free liquid may be a factor critical to the thermal process. The mechanical vacuum must be monitored at the closing machine vacuum gauge and recorded with sufficient frequency to document that the vacuum is at or above the specified reading during processing. Failure to maintain the mechanical vacuum at or above the vacuum specified in the filed scheduled process may affect heat penetration into the product. When % free liquid is a critical factor this must be monitored at sufficient frequency to insure control, prior to processing.
Other Critical Factors - Products susceptible to discoloration when contact is made with the metal container such as crab meat are sometimes packed with a full parchment paper liner, or a liner on just the ends of the containers. The parchment liner is designed to prevent the product from contacting the metal container. When crab meat is in contact with the metal container during processing and storage discoloration can result from the reaction of the product and the tin in the container. During the inspection of processors using parchment paper liners it is important to determine if the process being used was designed for use with a parchment liner. The addition of a parchment liner to the container inhibits the transfer of heat to the product during processing, and the processes for parchment lined containers may be longer to provide the same thermal process at the same processing temperature as containers without liners.
EXHAUSTING OF CONTAINERS
The exhausting of containers of lacf must be controlled so as to meet the conditions for which the process was designed. Exhausting of containers is designed to remove the air from the container and to provide a vacuum in the container. Air remaining in the headspace of the container contains oxygen which may interact with the product and the container increasing the rate of deterioration. Vacuum is measured in terms of inches of mercury (Hg.). 30 in. Hg. indicates a complete vacuum, 0 in. Hg. indicates a lack of vacuum, and 10 in. Hg. indicates that 1/3 of the air has been removed from the headspace of the container. In the United States