Physical factors for canned products.

TM 38-400/NAVSUP PUB 572/AFMAN 23-210 MCO 4450.14/DLAM 4145.12

(e) Flat sours. Flat sours are caused

(d) Ventilation.

Where

sharply

by bacterial action, causing changes in odor, color, or

fluctuating temperatures and high humidity prevail, the

turbidity of the product, but not accompanied by gas

lack of proper ventilation may cause excessively high

production which would cause swelling of the can.

temperatures. Proper ventilation is one of the most

important factors in protecting foods, particularly in

e. Exterior can coating.

tropical areas. In extreme cases, it may be necessary to

(1) Purpose.

Exterior can- coatings are

open doors and use fans to induce circulation.

applied to protect the tin plate from external conditions

(e) Light.

Damage from light is

promoting rusting and, depending on the coating

restricted to products that are packed in glass or

specified, to camouflage the bright can surface.

transparent containers. Exposure causes color changes

(2) Types of coating. Three types of exterior

and may affect the flavor of foods containing or

coatings are used. Specification TT-C-495, Coatings,

composed of edible oils and fats.

Exterior, for Tinned Food Cans, lists these as follows:

d. Physical factors for canned products.

(a) Type I.

Precoated camouflage

(1) Subject to spoilage. Canned products

(O.D. colored coating applied to tin plate before can

such as meats, fish, poultry, vegetables, fruits, and

fabrication). Precoated cans do not have the side seam

juices are subject to several physical environmental

area coated as manufactured. Depending on contract

factors causing spoilage.

requirements, the side seam may or may not be striped

(2) Spoilage factors.

with O.D. lacquer following filling and sealing.

(b) Type II. Post-coated camouflage

(a) Rust.

Rust, unless it actually

(O.D. colored coating applied to the cans sometime

penetrates the can causing leakage, will not injure the

following filling and sealing).

contents or render them inedible.

(c) Type III. Precoated unpigmented

(b) Dents. Dents, unless so severe as

(clear lacquer applied before can fabrication-commonly

to cause leakage, do not indicate that the contents are in

called "gold coat").

an unsatisfactory condition.

(3) Labeling of coated cans. Precoated cans

(c) High

temperature.

High

will normally have completed label information

temperatures are detrimental to all canned provisions

lithographed on the body or one end of the cans. Post-

and reduce the storage life to a considerable degree.

coated cans will usually show only the name of the

(d) Freezing. Freezing causes loss in

product or an abbreviation thereof since these cans

palatability and may cause breakdown of the texture.

have to be labeled after coating, and equipment for

Alternate freezing and thawing may cause delamination

complete labeling is impractical for the packer to

of the protective enamel.

maintain. While it is intended that most post-coated

(3) Major defects.

cans will have as near as possible the full name

(a) Quality change. Fading of color,

stamped on the side or one end, there is the possibility

loss of flavor, or softening of contents is due to chemical

that some cans will be embossed or impressed on the

action and the natural aging process.

end only with an abbreviated legend (see MIL-L-1497).

(b) Discoloration.

Discoloration of

f. Storage periods.

contents on the inside of a can because of chemical

(1) General.

Table 5-3 "Dry Storage of

action is found usually in products containing sulfur

Semiperishable Subsistence" should be used only as a

compounds (i.e., corn, peas, and meat products).

guide. This table is based on the optimum rather than

(c) Swells.

Swells, springers, and

the maximum storage life.

flippers are caused either by chemical or bacterial action

(2) Overaged stock. Activities receiving a

or by overfilling. Regardless of the primary cause, cans

pack older than that indicated on the storage life table

exhibiting such defects should be discarded or referred

should not on this basis alone consider the product as

to a medical or veterinary officer for recommendation as

unfit or undesirable. Subsistence stored for periods in

to disposition.

excess of the storage life shown in the table, but at

(d) Pinholing. Pinholing is due to the

temperature lower than those listed therein, should not

chemical action of the food acids on the tin. Pinholing is

be automatically considered as overage stock.

more often found in enamel-lined cans, brine- or

vinegar-packed items, and in waterpacked fruits.

5-56