246 SWEETENED CONDENSED Mik DEFECTS 
though the factory observes the most rigid attention to scrupu- 
lous sanitation and cleanliness. Most of these microbes are 
harmless and their growth is inhibited by the preservative action 
of the cane sugar. If, however, a poor quality of sucrose is used, 
which may contain traces of invert sugar, or acid, etc., many of 
these common species of micro-organisms, harmless in normal 
condensed milk, find an opportunity to develop and cause gase- 
ous fermentation. The presence of invert sugar makes unneces- 
sary the action of invertase in order to start fermentation; thus, 
microbes which do not secrete invertase and are otherwise harm- 
less, may become detrimental in the presence of invert sugar, 
added to the milk in the form of a poor quality of cane sugar. 
In a similar way the use in condensed milk of commercial glu- 
cose, as a substitute of a part of the cane sugar, and in order to 
reduce the cost of manufacture, is bound to cause disastrous 
results. Nothing but the best refined, granulated sucrose should 
be used, the best is the cheapest. 
Dangerous Effect of High Acid in Milk.—Acids have the 
power of inverting sucrose. The inversion by acid is especially 
active in the presence of heat. The milk in the vacuum pan is 
condensing at 130 to 150 degrees F. These temperatures are 
most favorable to inversion of a portion of the sucrose in the 
presence of acid. The higher the acid content of the milk, the 
more active is the inversion. Since invert sugar is the very 
ingredient necessary to cause bacterial action in the finished 
product, it is essential that the acidity of the milk to be con- 
densed, should be held down to the minimum in order to avoid 
trouble from this source. 
Contamination with Butyric Acid Bacteria.—Frequently the 
troublesome microbe is not a yeast, but helongs to a species of 
bacteria highly resistant to heat, and which fail to be destroyed 
by heating the milk to the boiling point. In this case, the con- 
tamination usually originates on the farm. Organisms of this 
kind, which infest the milk on the farm in this connection, 
largely belong to the butyric acid group. The most prominent 
among them are Granulobacillus saccharo-butyricus mobilis or 
Bacillus saccharobutyricus, Bacillus esterificans, Bacillus dimor- 
phobutyricus. The putrefactive forms of butyric acid organisms, 
