Guide to Inspections of Low Acid Canned Food 8
with the packing medium when the packing medium is held in the thermophilic growth range between 110 and 170° F. Packing liquids which are held for extended time period should be held at temperatures above 180° F. to prevent the growth of thermophilic microorganisms.
FILLING OF CONTAINERS-CRITICAL FACTORS
Filling of the container prior to the thermal process may be critical to the thermal process depending upon the product being filled.
Fill weight/drained weight- Fill weight is defined as the weight of the solid portion of product without the liquid prior to thermal processing. This differs from the drained weight of the product which is defined as the weight of the solid portion of the product with the liquid drained after thermal processing. Both fill weight and drained weight can be factors critical to the thermal process. Fill weight is easier to control as adjustments can be made to the filling equipment to keep the fill weight under control during processing. If fill weights are found to exceed the limits of the filed scheduled process, the deviation normally effects only small lots or portions of a lot. Corrections may be able to be made to this portion of the lot prior to thermal processing; or that portion of the lot may be set aside for evaluation by a processing authority.
Drained weight is controlled through control of the fill weight but cannot be evaluated until after the thermal process. If drained weight is found to be out of limits, it may involve the entire lot. In that event evaluation by a processing authority for commercial sterility ('minimum health process'), or destruction of the lot may be the only options available to the firm. Drained weights are also specified for meeting quality standards. The drained weights for quality/fill of containers standards should not be confused with the fill weights used to determine thermal processes for those products.
Fill weights are normally listed as a critical factor for all processes where a solid product is covered by a liquid packing medium. Fill weight may become more critical to the thermal process when agitation of the product is used to improve the heating rate of the product.
Containers can be filled by a variety of equipment depending upon the product and style of pack. Filling methods normally encountered include: hand packing (where the product and perhaps the covering liquid are added to each container by hand); volumetric filling (where a volume of product is accumulated in a pocket and dropped into the container); mechanical (where agitation vibration and shaking of the container are employed to adjust the fill); piston (where a certain amount of product is displaced by a plunger); and vacuum (where a vacuum is pulled on the container as the product is filled into the container). A volumetric filler is normally considered to be the same as a hand fill as long as no vibration or agitation of the container is employed during filling. Different ingredients as well as the covering liquids may be added to the containers in different stages. Methods of adding the covering liquid include: liquid falls (where the container passes under a continuous falling liquid film), piston pump (where a predetermined amount of liquid is pumped into the container) and volumetric (where the liquid is measured mechanically into a chamber with a predetermined volume).
Fill of container is normally measured with a balance, electronic or other type of scale. Homogenous liquids may be measured by volume if data exist that supports the volumetric fill measurement method. For products packed by hand each container may be weighed and the contents adjusted to meet the fill weight requirements. This is especially true for very expensive lacfs that are hand packed such as caviar and crab meat. For other products the fill weight/drained weights should be checked at a frequency which will ensure that the requirements listed in the firm's filed scheduled process are being meet. The closer that a firm operates to the filed scheduled process parameters the greater the need for more frequent checks of fill weights. The lacf regulations (21CFR 113.40- see the 'Critical Factors' section of this guide) recommend that all critical factors should be measured at a frequency not to exceed 15 minutes. If a firm is not operating close to (within 5% of) the acceptable control limits and fill weights are being adequately controlled, 15 minutes may be an excessive requirement for fill weight checks. However, as a basic rule of thumb, fill weight checks should never exceed one hour.
Headspace -The container headspace may be a factor critical to the thermal process, especially for agitated products which need the gas bubble provided by the headspace to induce agitation into the product. Headspace is normally controlled by filling the container from a chamber with a predetermined volume; through the use of a mechanical tamper after filling (which comes down into the container forcing the solid products below the level of the liquid and excess liquid product out of the container); or by filling the containers to the top and then conveying them on an inclined conveyor which allows excess liquid to flow out of