60 BULLETIN 1370, U. S. DEPARTMENT OF AGRICULTURE 
taking care not to place the cases of hot cans in large stacks, where 
temperature and circulation of air are unfavorable for rapid cooling. 
Whenever it is necessary to pile them in large stacks, they should be 
“stripped;”’ that is, narrow strips of wood are placed across the 
stacks at intervals of every three or four rows of cases, thus permitting 
air to circulate through the stack to accelerate the cooling. 
CANS AND CANNING EQUIPMENT 
By C. F. Watton, Jr., Bureau of Chemistry, U. S. Department of Agriculiure 
Friction-top cans are generally preferred for small-scale canning, 
because they can be readily closed by hand. Only one serious diffi- 
culty exists in connection with hand canning—that of always obtain- 
ing perfect closure of large and small friction-top cans. Ordinarily, 
if the sirup is consumed fairly soon after it has been canned, there is 
no serious trouble from fermentation. The canning operation, 
however, even if it has not been properly done, is likely to give 
sirup makers a sense of security. Unless the closure with friction 
tops is perfect, air is drawn into the can as a result of the partial 
vacuum caused by the cooling of the hot sirup. The sirup thus 
becomes infected with microorganisms present in the air. Although 
fermentation usually takes place more slowly in cans than in barrels, 
and in only comparatively few cans, in time the contents of such cans 
become unmarketable. A much higher percentage of perfect closures 
is obtained with the small friction-top than is possible with the large 
friction-top cans. These statements refer exclusively to closure of 
friction tops by hand. Mechanical devices for inserting the tops now 
on the market give satisfactory results; and, as certain market 
territories prefer them, the small friction-top cans are still used by 
some of the larger packers. 
The sanitary can and the solder-top can are the most satisfactory 
types for larger canning plants, which have special machinery for 
filine and closing the cans. Soldering small friction-top cans by 
hand immediately after closing, while the sirup is still hot, gives a 
perfect closure, but is troublesome and seldom done. Soldering by 
means of a mechanical device can be done on a large scale, however, 
so that solder-top cans are sometimes preferred by the larger sirup 
canners. 
The most popular can for large-scale operations is the sanitary 
can, used exclusively by many of the largest sirup packers for all 
situps. As a mechanical closmg machine is required to close this 
can, however, it is not suitable for use on a small scale. 
In canning sirup on a scale corresponding to that recommended 
for a central canning plant (p. 66), a sirup-fillinge machine automatic- 
ally fills the cans with a weighed quantity of sirup. The filled cans 
are carried on a belt conveyor to the closing machine, where they are 
automatically closed. A mechanical conveyor then carries them 
through a washing machine, consisting essentially of a box of rec- 
tangular cross section containing running water, where sirup adhering 
to the outside of the can is washed off. The cans pass directly from 
the washing machine to the top of a gravity roller conveyor, over 
\which they roll for a short distance to the labeling machine. After 
being labeled, the cans are packed in cases and stacked in such a 
manner as will permit rapid cooling. 
