Where more than one time is given for the processing, it is to take care of the difference in the degree of ripeness, and the water content of the fruit. Gooseberries need very little processing and plums will require less. Plums exhausted at

212° for five minutes can usually be closed and stored without processing.

The exhausting and processing of each variety of vegetable will be treated under the heading of the variety desired in Part II of this work, Detailed Consideration of Various Products.

Processing Under Pressure

In processing cans under pressure, there are several things to take into consideration. First of all is that the cans while in process have a greater pressure on the inside than there is resisting pressure on the outside, owing to the fact that it is impossible to close the cans with the same temperature as in the process under pressure. This, however, can be reduced to a minimum by having the product as hot as possible before closing.

Some commodities are cooled by spraying cold water on them before they are put into the can, and then the hot brine is added and the can closed. If the can is shaken and the temperature taken it will be found to be 40 to 80 per cent lower than when the cans are run through an exhaust and thoroughly heated before closing. This applies particularly to number 10 cans.

The proper way to equip a retort is to tap as near the top as possible with the same size pipe as that bringing the steam in at the bottom, usually one inch. Also connect to the bottom exhaust a water line which has more pressure to the square inch than the processing pressure on the retort. With this completed and the retort filled with properly filled and exhausted cans, it can be started in the usual way, and after the usual process time, open the steam line over the top and close the steam line entering at the bottom.

Start the water at the bottom and allow it to gradually fill to the one-foot level, retaining the process pressure by steam regulation over the top of the cans.

When the retort is full of water the steam can be shut off and the water released by top exhaust valve, the water pressure being maintained until all danger of strain has passed, but great care should be taken to avoid retaining the pressure too long, as the cans may collapse from the heavy outside pressure.

Fourteen to fifteen pounds pressure of steam will give a

temperature of 240° F. and twenty pounds pressure will bring the temperature up to 260° F. The retort cannot stand a twenty-pound pressure without one foot of water in the bottom.

Note: Blanching, exhausting and processing is also treated under each variety of fruits and vegetables in Part 2. Swells and Springers

(Taken from Bulletin No. 2, by W. D. Bigelow, National Canners' Association)

A swell is a can which has undergone decomposition by micro-organisms, accompanied by the generation of gas, which first releases the vacuum and then causes pressure in the can. This decomposition is often of putrefactive nature and may be rapid or slow, according to the organism and temperature.

Swells are due either to defective sterilization or to leaky cans. It is sometimes difficult to measure the heat conductivity of a given product. Fruit which is thoroughly ripe has a tendency to cook up more than fruit that is greener, and thus lessen the heat conductivity of the liquid in the can. In the case of many products, such as corn, the heat required to penetrate to the center of the can increases with the consistency of the product. If the processor underestimates the ripeness of a batch of fruit, therefore, or the consistency of a homogeneous product, or the amount of sugar added, swells may result.

Owing to defects in the manufacture of the can, or in the plate from which the can is made, there are occasional leaks, sometimes so small that even when filled with air under a pressure of 20 or 30 pounds the air that bubbles through them when placed under water is in such fine particles that it is difficult to see. When such cans are filled with food the bacteria that pass through these openings cause decomposition and when pressure results the openings are sometimes closed by particles of food and are difficult to find.

A "springer" is a can whose ends are more or less bulged, owing to pressure from hydrogen generated as a result of the chemical action of the contents on the metal of the container, or because the can was overfilled or insufficiently exhausted.

In springers where the pressure is caused by overfilling the can, or by insufficient exhaust, this pressure does not increase with time, but remains constant except as it is influenced by temperature of storage. The ends of the cans are somewhat distended and may be easily pressed into place with the fingers. When the fingers are removed the ends may resume a convex position, or may remain concave, or flat (according to the pressure within the can) until the can is jarred, and sometimes until the temperature to which it is subjected is increased.

When the pressure is due to hydrogen generated by the action of acid fruits on the metal of the can it is ordinarily taken for granted that the hydrogen thus generated is due to the action of the acid of the fruit on the tin. I [W. D. Bigelow] think this is a mistake. I think it results in large part, at least, from the action of the acid on the iron and that the amount of hydrogen liberated in the can is usually a measure rather of the iron that has been dissolved than of the tin. The metallic taste in a product of this nature is certainly due to dissolved iron. Of course, where any great amount of iron is dissolved in the product, the tin is also dissolved, but passes largely into an insoluble form.

The natural acids of the fruits attack the container, dissolving the iron and carrying tin into the food and into the liquor, where it is largely, often chiefly, precipitated in insoluble form. This liberates hydrogen, which directly causes springers. While in the nascent state this hydrogen bleaches many of the colored fruits. When lacquer is used in an attempt to prevent this action pinholes often result, leading to the spoilage of a considerable percentage of the pack, and with some products an undesirable flavor is imparted by the lacquer. These difficulties all come from a common cause and will only be overcome by understanding and removing the cause. This statement, however, does not include the solvent action of the metals of the can of amino bodies in certain foods, such as shrimp, pumpkin and asparagus.

According to the amount and character of the fruit acid present, the tin and especially the iron of the container are more or less attacked, the latter causing astringency, which is often called the "tin" taste of some canned food, and yielding springers of the class we are now discussing. Since the action