CANNING FOR WINTER USE. 281 



it is by boiling tlie material to be canned that these organisms are to 

 to be killed. 



Water boils at a temperature of 212 degrees, and when the tem- 

 perature is maintained for several minutes, or even as much as two 

 hours, most of these organisms of decay are killed. However there 

 are some which, in certain stages of their growth can resist even pro- 

 longed boiling, and in the course of time bring about the decomposi- 

 tion of the canned product. To overcome this, canners, both at home 

 and in the factory, have resorted to the use of a closed vessel in 

 which to do the boiling, so as to take advantage of the steam pressure, 

 which materially increases the temperature of the water. For the 

 usual kind of easily-canned vegetables, steam pressure canning reduces 

 the time of cooking, and for those things which are difficult to can it 

 increases tl;..- assurance of having the produce "keep." 



There are several different makes of canning machines on the 

 market, but they are all the same in principle — that is the application, 

 of heat to the product to be canned. Most of these are the "open 

 kettle," in which the cooking is done at the temperature of boiling 

 water; while some of them may be closed and the cooking done under 

 steam pressure. But in either case, one operation which is frequently 

 necessary in preparing the fruit or vegetables for the cans, is that of 

 "blanching." 



In the language of the housewife, this is nothing more than par- 

 boiling, or dipping the fruit or vegetable in boiling hot water for a 

 few minutes, for the purpose of extracting or drawing out some of 

 the bitterness of the skin, which, if allowed to remain, would do more 

 or less harm. In the ordinary canning operations this blanching is 

 done by placing the article to be blanched in a screen vessel or one 

 having many perforations through which the boiling water can quickly 

 pass. Where the recipe for canning any certain fruit or vegetable 

 says that it must be blanched, it is very important that this be done in 

 order to secure the best grade in the packed product. 



"Exhausting" is an operation in which commercial canners differ 

 to a slight extent, some preferring to exhause their cans before sealing 

 them up tight and others omitting this operation. However, the pur- 

 pose of this operation is to drive the air out of the can so as to prevent 

 its expanding and bursting the can when the heat is applied. Exhaust- 

 ing is most necessary with those articles which are cold when put into 

 the cans, and in less where they have been heated, as with those which 

 have been blanched and the cans filled with hot syrup. To exhaust 

 can is to heat it to the boiling point before it is sealed up tight. This 

 expands the air in the can, and some of it passes out of the little hole 

 in the center of the lid, after which this little hole is closed with 

 solder in the operation called "tipping." But while each of these 

 operations is important, the most important of all is that the. "pro- 

 cessing." This is the final cooking of the material to insure it against 

 decomposition. In processing, the sealed cans are placed in the 



