458 STATE BOARD OF AGRICULTURE 



PART II 

 Bacteriological Studies of Flat Sours of Cold Packed Canned Peas 



ZAE NORTHRUP WYANT AND ROBERT L. TWEED 



An attempt has been made to discover the organisms which cause flat 

 sour of cold packed canned peas. No extensive bacteriological study of 

 flat sour has been made up to the present time. Consequently, the available 

 information both as to the nature and cause of flat sours is very limited. 



In ''Canners' Problems" (1) Bronson Barlow says: 



'' 'Flat sours' are not caused by the heating and souring of corn before can- 

 ning. Corn which was purposely allowed to heat and sour in the can was 

 canned and was not flat sour. These cans did not develop flat sours on 

 keeping." Barlow also says with regard to the organisms concerned: 

 "Stains from flat soured corn show long, slender rods, often in chains." 



In "The Canning of Fruits and Vegetables" (2) Zavalla makes the state- 

 ment: "Spoilage due to insufficient processing is generally divided into two 

 classes: swells and flat sours — ^flat sours most often result from giving the 

 regular process to material which has been allowed to stand for some time, 

 such as peas remaining in a load over night, or corn left in a car or in a pile 

 until it begins to heat." The contradiction in the above references shows 

 that the work on "flat sours" is still in an experimental stage. 



In "Canning and Preserving of Food Materials" (3) by E. W. Duckwall, 

 the author says : 



"Sour peas in many cases are due to careless methods before the sterihzing 

 process : there is no part of the process of pea-canning which affords so much 

 danger of sour goods as the sweating of the vines and pods. One peculiarity 

 of sour peas is that it is impossible to tell by the appearance that they are 

 sour." Later he says: "I boiled twelve cans in an open bath for two hours, 

 then put them in the incubator. Five spoiled within one day, three spoiled 

 by the end of the second day, and two more swelled the following day. Two 

 cans seemed to be all right. They did not swell, though kept at blood tem- 

 perature for three weeks. On opening the cans, however, they were exceed- 

 ingly sour. The color of the peas was much bleached, but otherwise they 

 looked fairly well. I melted a flask of agar in the autoclav at 240°F. I 

 inoculated two with several loops full of the hquor from these cans then 

 made transfers from the first to two more, and from these made transfers 

 into two more. I placed the dishes in the incubator, and at the end of twen- 

 ty-four hours the first two dishes were completely covered with a thin growth 

 extending even up to the walls. The next two dishes had a few colonies, but 

 the greater portion of the surface was covered with a spreading growth. 

 The two last dishes contained a few scattered colonies, which formed in wedge- 

 shape below the surface and grew upward, forming thin, round colonies on 

 the surface. Some of these colonies had a brown, opaque granular appear- 

 ance by transmitted fight, but on reaching the surface had a bluish cast wit'i) 

 a shining transparent luster. The surface growth extended gradually to 

 about the size of a silver three cent piece, the lustrous appearance giving 

 way to a dufi scum-like layer, quite viscous and forming folds or wrinkles, 

 becoming much elevated. 



