8 THE BOOK OF FRUIT BOTTLING 
exact degree of heat required to destroy the germs varies 
considerably according to the object which is being 
sterilised; in fact, some fruits and some vegetables, 
require three or four successive sterilisations (by which 
first one bacteriological family and then another are 
destroyed) to bring about the required conditions. 
The hot air and steam by which the bottles in the 
steriliser or other vessel are now surrounded causes the 
water or Juice zmside the bottles to get hot and expand 
until it reaches the air-tight capsule or cover. The 
requisite temperature is sustained for some time at an 
equal height until the process is complete (this can be 
determined to a nicety by the fixed thermometer), and 
the bottles are either lifted out and put intoa cool place, 
or else cold water is turned into the machine whilst the 
bottles are in it (the hot water having been previously 
drawn off), With the decreasing temperature a vacuum 
is created, and unless the caps or tops are imperfect or 
imperfectly adjusted, and so admit the air, the contents 
of the jar, as before stated, will keep for any length of 
time, because germs donot incubate in a vacuum. This, 
then, is the theory carried out by the process of sterilisa- 
tion. If sufficiently complete—and, as before stated, the 
requisite temperatures for the different fruits and 
vegetables have been proved, and these temperatures 
are registered by a thermometer—the vacuum is attained 
and the germs made sterile. It may chance, however, 
that the rubber bands or the caps are not placed on the 
bottles quite evenly, or if the cap is screwed that the 
screw ring is not quite perfect, then, if from one cause or 
another air is admitted, as a certain consequence the 
vacuum is destroyed, the germs come into life, and 
immediately begin to cause decay and decomposition or 
fermentation. If this is not at once noted, and the 
batch of bottled fruit re-sterilised and re-capped, it will 
all go bad, and very bad too, especially in the case of 
