266 UNSWEETENED CONDENSED MiLK DEFECYS 
Blown Evaporated Milk (Gaseous Fermentation). 
General Description.‘The ends of the cans bulge out very 
noticeably, frequently so much so that the seams of the cans 
burst open. ‘This 1s due to gaseous fermentation causing high 
pressure in the cans. ‘The pressure is often so great that upon 
opening the cans, most of the contents are blown out with tre- 
mendous force. [n some cases of blown evaporated milk, the 
contents have an acid odor, pleasant and aromatic. In most 
instances, however, they give off very foul odors and suggesting 
hydrogen sulfide, not unlike aggravated cases of Limburger 
cheese. ‘These odors are exceedingly penetrating and difficult to 
remove from anything they come in contact with. 
Causes and Prevention.—The bacteria causing gaseous fer- 
mentations in evaporated milk usually belong to the anaerobic 
group of butyric acid species and in most cases, though not al- 
ways, the putrefactive types prevail, such as Bacillus putrificus, 
Plectridtum novum and Plectridium foetidum, especially the lat- 
ter, because of its extraordinary power of resistance to heat. 
Plectridium foetidum is an obligatory anaerobe and it absolutely 
refuses to grow under aerobic conditions. It is an actively motile, 
medium-sized organism with flagella and spores. At one end it 
has an Indian club-like enlargement, in which appears the spore. 
The bacillus resembles a kettle-drum stick similar to B. tetani. 
Under strictly anaerobic conditions, and incubated at 90 degrees 
F., it ferments milk in four davs. ‘The milk first curdles, then 
gradually the curd dissolves (digests) completely, leaving a clear 
yellow lquid, similar in appearance to butter oil. The fermenta- 
tion is accompanied by the evolution 
fa penetrating foul odor. 
This organism survives exposure for 15 minutes to 245 degrees 
FP. Its thermal death point lies between 245 and 250 degrees F.t 
Plectridium foetidum, as well as most of the other species of 
anaerobic, spore-bearing butyric acid bacilli and bacteria, is 
present abundantly im cultivated soil, in field crops and even on 
the kernels of the grain. Since this tvpe of evaporated milk 
defect is characteristic, especially, of the product manufactured 
during the late summer and early fall months, it is very probable 
that the dust incident to the harvesting of the field crops, fur- 
1 Hunziker, A Study of Gaseous Fermentation in Evaporated Milk. 
