LPT 321: Meat Science (1+1)

CANS - TYPES OF CANS

• As a food containers, the metal can possesses certain virtues possessed by no other type of containers for heat processed foods, viz.,
  • It has a high conductivity, which is of importance during processing.
  • It cannot be easily broken.
  • Being opaque, any possible deleterious effects of light on the foodstuffs are avoided. 
• Although, the term ‘can’ is applied to modern containers, this is somewhat of a misnomer, as they are constructed of mild steel with a thin coating of pure tin.
• The actual amount of tin being only about 1.5 % of can’s weight. It is important that the tin used should not contain more than 1% of lead.
• Coating of steel plate is necessary to prevent corrosion for steel is an unstable compound and in some foodstuffs, such as fish or fruit. The tin plate is protected by a fish or fruit lacquers.
• Unsightly staining of surface of certain foodstuffs known as sulphiding may also occur and is avoided by use of a phenolic meat lacquer or a sulphur resistant lacquer.
• An alternative method of avoiding sulphiding is now being extensively employed for meat pack and consist of chemical treatment of the inside of the can to form an invisible protecting film a solution used being a strong alkali bath containing phosphate and chromates.
• The design of cans and the techniques of can manufacture are being constantly researched on and developments are constant in this industry.
• Two of the most important advances achieved by these research activities is the great reduction of metal in the cans and the replacement of soldering, which involved use of lead by electrical welding.

Types of Can

• Three types of cans are mainly in vogue currently  and they are the three piece food can, two piece drawn and wall ironed can and drawn and redrawn can.

Three Piece Food Can

• Tinplated steel, coated with lacquer, so as to prevent contact between the tinplate and the food to be canned, and dried in ovens for 15- 20 minutees is cut into strips of specific   lengths and widths as per the size of the cans desired.
• Such individual strips are then rolled into cylinders and the two edges of the cylinder drawn with an overlap, which is electrically welded.
• At this stage the cylinders are further given a coating  of lacquer on the seams and dried in ovens
• A lip is next formed on each end of the of the cylinder.
• Seperate ends (lids and bases) are made in a different area and the rims of these ends are curled and a  sealing compund is injected into the curl.
• The base is next joined to the cylinder body, the sealing compound forming an airtight seal.
• The cans, with the seperate lids are ready for use.

Two Piece Drawn and Wall Ironed Can

• These cans consists of two pieces of tinplate, the body and base being formed from one piece of metal and the lid from another.
• The body and base are shaped from a thick piece of tinplate which is drawn up, ironed and ridged for strength and then given a coat of lacquer.

Drawn and Redrawn Can

• Drawn and redrawn cans are manufactured from two pieces of tinplate , the body being made from a disc shaped piece lacquered on both sides and drawn up to form a shallow cup and then drawn and redrawn to form a deep cup.