SWELLS. (See Canned Goods.) With regard to this subject a writer in the Packer's Review says: " At the beginning, in discussing the subject of swells, it is well to observe that all vege table matter after the process of growth is discontinued begins to decompose. Decomposition is its inevitable fate sooner or later. It is for the purpose of arresting this change that the packer exerts his efforts. Decomposition takes place by regular processes, which are governed by as well-defined laws as growth itself. The first step in decomposition is fermentation. It is of this principally that we shall speak. There are two kinds or two stages of fermentation—the alcoholic and the acetous. To under stand fermentation it is necessary to know that all vegetable mat ter contains, besides other ingredients, sugar, water, and some of the albumens, such as gluten, albumen, and caseine. For sim plicity, let us say that all vegetable matter contains sugar, water, and gluten. The first fermentation is the alcoholic. The gluten exposed to the air and moisture, putrifies ; in so doing it acts upon the sugar, resolving it into water, carbonic acid gas, and alcohol. Having gotten thus far, we are now in a position to ex plain the object of sealing vegetables hermetically, and why they keep when so sealed.
"We have seen that fermentation begins by putrefaction of the gluten ; by this process a yeast is formed, which is the actual ferment. This change of gluten into yeast cannot be accomplished without the presence of oxygen, which is the vital principle of air. We now can perceive that by excluding the air we remove one cause of decomposition. It may be further observed concerning yeast that it is itself a growth, a germination of microscopic plants. The most potent destroyer of life is excessive heat. We can now understand the object of heat in the operation of pre serving vegetable matter, It not only excludes the air, but it destroys the germs of decomposition. Taking up now a can of fruit or vegetables, let us observe the conditions necessary to its preservation : "First : There must be expelled from it as much as possible of the superfluous air and the can made perfectly air-tight.
"Now let us suppose that a can has a leak. Through this leak the contents of the can become exposed to the air and fermentation ensues. Whether the presence of fresh air is sufficient to revive the dormant properties of the ferment, or whether the air itself bears with it the germs of decomposition, as it does the germs of disease, is a question as yet not fully decided ; we are inclined to the latter opinion. Perhaps both facts are true ; circumstances within our experience would seem to justify both theories. In the course of fermentation, induced by the admission of fresh air into the can, carbonic acid gas is thrown out. If this gas arises more rapidly than it can escape through the leak, the can swells by the pressure of the confined gas. If the leak is in the top of the can, the swelling is augmented by the fact that the escaping gas forces to the top of the can the solid portion of its contents, thus further hindering the exit of the gas by obstructing the pas. sage. In such cases the can frequently bursts. Having described the effect of a leak, we may now inquire into the effect of a bad process, or, in more definite words, the application of insufficient heat.
" Heat may be said to be sufficient when it will destroy all the germs of decomposition. The amount of heat varies for different substances, and is by no means uniform for any one substance. If insufficient heat be applied to a can, in a short time after pro cessing fermentation begins. The live germs and the least bit of air the can contains are doing their work ; we say the air the can contains, for it will contain some air, however well it may be ex bausted. If there be sufficient air in the can, the contents will swell and burst the can. Sometimes the quantity 3f air in the can will not generate sufficient carbonic acid gas to explode the tin, although it will be swollen, or at least be a spring bottom.