240 SWEETENED CoNDENSED Mik DEFEcTS 
The empty tin cans in many of the plants are kept under 
undesirable conditions. They are exposed to diverse channels 
of contamination during transportation to the factory and dur- 
ing storage in the factory. If these contaminated cans are sub- 
sequently filled with the condensed milk, contamination is un- 
avoidable and buttons are likely to follow. 
The tin cans should therefore be protected against avoidable 
contamination, or better vet, they should be sterilized before 
filling. 
A practical sterilizer of empty cans may be readily devised 
by permitting the cans to pass bottom-side-up over a series of 
gas flames, under a hood. This method is used successfully 
in some of the European condenseries and has for them solved, 
in a large measure, the prevention of buttons. The caps and 
filling machines obviously should receive such treatment as to 
prevent them from becoming sources of contamination. Barrels 
should be steamed till piping het and then paraffined, before 
filling. 
In factories with wooden floors where the filling and sealing 
is done, the danger of mold contamination is much greater than 
in the case of concrete floors. 
According to Thom and Ayres? the spores of the mold Asper- 
gillus repens, as well as of most other common molds, are killed 
in 30 minutes at. 140 degrees F. The preheating of the milk in 
the hot wells, which is done at 180 degrees to 200 degrees F., 
and again evaporation in the vacuum pan at 135 to 150 degrees 
F. are, therefore, sufficient to destroy any mold present in the 
original milk, so that the cause must be confined very largely 
to contamination after the finished product leaves the vac- 
uum pan. 
Low Temperature.—The growth of most molds is retarded, 
if not entirely inhibited at low temperatures. This also is the 
case with the button-forming mold Aspergillus repens. Rogers 
et al., state that this mold grows very poorly at temperatures 
of 68 degrees F. or below. ‘hey report that they have never 
1Thom and Ayres, Effect of Pasteurization on Mold Spores, Jour. Agr. 
Res., Vol. VI, 153-166, 1916. 
