Canning and Fish Packaging Technology

Unit 3 - Unit operations in canning

3.2.2.4.1.Head space in cans
In any food can, food and the filling medium do not occupy the complete space available inside the can. Some vacant space is available and this is known as head space. It is measured after the lid is cut open. Gross head space is distance between outer most point on the seam and the level of food inside the can. This includes countersink and thickness of the tin plate. When the sum of countersink and tin plate thickness is deducted, net head space is obtained.

Gross head space = Net head space + Countersink + tin plate thickness
Net head space= Gross head space - (Countersink + tin plate thickness)

As countersink and tin plate thickness are constants, it is customary for some processors to measure only gross head space rather net head space.

In food cans, for small sized cans gross head space should not be more than 5 to 7.5 mm and for large cans not more than 16 mm, for medium size cans it is 10 mm.