VACUUM IN THE CAN
Prior to application of the packer's end, a vacuum is applied to the headspace.
(Headspace is the nonfilled portion of a container that allows for product expansion. A
vacuum is the result of a process whereby air and/or free gases are removed from the
container.) Vacuum is applied for numerous reasons, but primarily to prevent bacterial
growth. Other important reasons for a vacuum are to prevent oxidation or rancidity of
the product, preserve vitamins, and to provide space for expansion of gases during
retorting. A vacuum can be drawn on the can by vacuum closing machines, preheating
the product, using an exhaust box, or by injecting steam into the headspace of the can.
The can style varies with the product it is to hold. The ends are differentiated as
manufacturer's end (put on during fabrication) and packer's end (put on by the
contractor after the can is filled, normally with embossing, showing can code
information). Can styles have been given names according to the characteristics of the
can. See Figure 1-4. Some of the different kinds of can styles are:
a. Sanitary (Open Top). These are round in the cross section and have
double-seamed ends. A sanitary can is always sterilized after it has been packed and
sealed. This is the most common style of can in use today.
b. Extruded (Drawn). Cans that are round, oval, or oblong in cross section are
extruded cans. These have a one-piece, drawn body, have only one double-seamed
end, and have either a crimped-on or a soldered-on end. The lid may be scored for
opening with a key or finger pullring. Some items packed in extruded cans are
sardines, anchovies, herring, jellies, desserts, and military rations.
c. Square, Rectangular, or Oval. Some cans are square or rectangular in
cross section and have double-seamed or soldered-on ends. These cans are
commonly used for luncheon meat, hams, loaf-type items, and survival packets. The
oval cans are also known as pear-shaped cans.
d. Hole and Cap or Vent Filler. These cans are square, round, or rectangular
in cross section. They have double-seamed or soldered-on ends, and are used to
package evaporated milk and anhydrous milk fat. The final closure is a soldered cap or
a vent hole filled with solder.
e. Beaded Cans. These have indented grooves around the circumference of
the can body that are parallel with the double seam. Beading increases resistance to
paneling by up to 150 percent. It is used mainly on larger cans that tend to have