34 BULLETIN 1265, U. S. DEPARTMENT OF AGRICULTURE 
touched upon in the present experimental work. The relation of 
scalding to the keeping quality of the canned foods is one of these. 
RELATION OF SCALDING TO KEEPING QUALITY. 
The impression prevails with many that scalding has a direct, 
favorable bearing upon the keeping quality of canned foods, and 
that the process in itself has great value from a bacteriological 
standpoint. The matter warrants the most careful consideration, 
and it is proposed to investigate this point. 
To favorably affect the keeping quality of foods, and justify any 
modification in the severity of processing operations, scalding must 
do certain things: (1) Facilitate heat penetration, and (2) bring 
about an actual destruction of the microorganisms which cause 
spoilage or reduce their resistance to heat. 
That preliminary scalding assists in cleansing the food materials, 
and may wash away many of the bacteria with which they are con- 
taminated, is too well known to require discussion, but this reduc- 
tion in contamination does not mean that the processing tempera- 
tures or time periods can be reduced. 
It is conceivable that occasionally raw material might be cleansed 
of all spore-formed bacteria by scalding in boiling water, and thus 
the subsequent processing might be reduced in severity, but there 
is no way at present of knowing when this condition has been at- 
tained ; and for the sake of safety in food preservation, the reduction 
of the processing temperature and time periods must be looked 
upon as a matter too risky to be considered seriously. 
A fact commonly overlooked is that the water of the scalding bath 
may actually contaminate the raw materials being treated in it by 
transmitting to them the spores of microorganisms derived from 
material previously scalded in the same water. This may occur 
especially when the same water is used repeatedly. To what extent 
contamination of this kind takes place in actual practice is unknown, 
but the possibilities of its occurrence decrease more and more as 
sanitary measures are observed. It presents another reason, however, 
why in the scalding process clean fresh water must be used. 
The influence which scalding as a preliminary canning operation 
has upon the destruction of microorganisms calls for careful con- 
sideration. 
That a brief treatment in boiling water is of great value in de- 
stroying the vegetative forms of many bacteria and other micro- 
organisms is unquestioned. But it is not so much with these that 
the real problems of food preservation are concerned. Were it not 
for the fact that many of the bacteria responsible for spoilage in 
canned foods form spores which are very resistant to heat, the 
preservation of foods would be relatively simple. Processing opera- 
tions must be directed, therefore, to the destruction of these highly 
resistant forms. 
No attempt has been made to bring together all the literature 
bearing upon this particular phase of the subject, and reference will 
be made to the reports of but a few investigators. Globig (29) re- 
ported studies on a potato bacillus killed in streaming steam at 100° 
C., only after 5 to 6J hours' exposure. Christen (23) described an 
