Meat Science

OUTLINE OF CANNING OPERATION

Preparation of the raw material (meat)

• The handling of meat prior to heat treatment is very important.
• Meat should be handled hygienically and under strict temperature control so that contamination is avoided and the multiplication of microbes is prevented.
• The long-term storage of meat intended for canning should be preserved under a temperature of –12°C to –18°C.
• A variety of processes like grinding, trimming, cutting, washing, canning, mincing, dicing, addition of emulsifiers, binders and other supplements should be carried effectively and rapidly.
• Meat should be thawed in special thawing rooms or in chillers.
• The meat and its offal intended for pet food manufacture are not thawed but minced and diced in frozen state.
• Most canned meat products are salted because it does reduces the heat resistance of bacterial spores and thereby reduces the cooking time also.

Precooking / Blanching

• Products like meat is precooked whereas, vegetables and fruits are scalded or blanched in hot water at a temperature of 87°C to 95°C or exposed to steam.
• Blanching is done to
  • Remove the respiratory gases, which would reduce vacuum in the can.
  • Inhibit the enzymatic action, which can reduce quality and nutritive value of meat.
  • Cause shrinkage of the product.
  • To clean the product.

Filling of cans

• Filling of cans is the critical part of the canning operation, which can be done mechanically or by hand, which should be done carefully.
• There are two types of can filling.
  •  Hand filling
  • Mechanical filling (Machines)
• Hand filling is generally employed depending on the size or configuration of the product.
• Products, which are susceptible for damage during mechanical filling, are subjected for hand filling.
• Mechanical filling can be done by a wide variety of semi or fully automatic mechanical fillers.
• In mechanical filling mostly comminuted products and products which have fine particle size are filled in.
• The steps in canning operations are as following

Exhausting

• The exhaustion is done by removal of air from the can before it is sealed.
• Exhaustion is necessary because
  • Can sealed without previous exhausting may show such expansion of the contents during possessing as to force the seams and produce a ‘Leaker’
  • It produces a concavity of the ends of the tins. So that, any internal pressure may be readily detected and the can rejected.
  • It lowers the amount of oxygen in the can and prevents discoloration of the surface of the food and corrosion of the can.
  • In fruits packs, it reduces the chemical action between the food products and the container thus, largely eliminate “Hydrogen Swell”.
  • Although the production of a vacuum, probably has very little effect on microorganism. Experience has showed that, tin containing a vacuum keep better than those from which the air has not been exhausted.
• Exhaustion of a can may be carried out in three ways, such as
  • Heat exhausting
    • The contents of the can are filled cold, which is then passed through steam produce in a exhaust chamber and heated immediately before sealing.
    • The ends of the can are loosely attached to permit of the escape of the air, sealing being completed when the can leave the exhauster.
    • The effect is to release air or gas trapped in the product.
  • Vacuumizing or Mechanical Exhaust
    • The cold material is filled in to the can, and then closed in a vacuum-closing machine, the can being subjected to a high vacuum during the seaming operation.
  • Steam Injection
    • This method involves injecting a blast of steam into the headspace as lid of the can is being positioned.

Sealing or seaming of the container (closure)

• The sealing of can after evacuation is achieved by curling the edge of the lid over the can.
• The sealing material often a synthetic rubber compound must retain its resilience over a temperature range from below room temperature to above 130°C.
• Sealing is done by a double seamer and the sealing operation takes about one second.
• There are two seaming operations.
• First is seam operation and the other is the hermetic seal operation.

Thermal Processing / Sterilization

• After exhausting and closing the cans must be heated for an accurately predetermined time and temperature in an atmosphere of saturated steam in heated water or occasionally in an air steam mixture.
• Food to be canned is threatened on one hand by spoilage due to bacteria and on the other by damage of overheating.
• The canner, therefore, choose a middle course, the minimum heat employed in processing being controlled by the nature of food in the cam and types and number of bacteria likely to be present.
• During processing, heat penetrates to the center of the can by conduction and by convection currents.
• In the solid meat pack the diffusion of heat is brought about by conduction and the process is therefore slow.
• Solid loosely packed in a liquid will, therefore, heat more rapidly due to convection current than those, which are tightly packed.
• pH or the acidity of the food contents also has an important bearing on the temperature required for processing.
• Acid foods, which include the common fruits, are easily processed.
• The temperature must be sufficient to kill yeast, moulds and certain bacteria capable of growing in the acid medium.
• In non-acid foods, such as meat, the destruction of the bacterial spores is slow and these foods require temperature of 115°C with sufficient time (45 minutes).
• A serious problem associated with conduction heating is time. When small volume of product at the can center is sterilized, the peripheral portions are severely over cooked.
• To avoid this agitation during cooking and the presence of headspace not only minimizes the uneven treatment but effectively the temperature and time required for safe processing.
• Rotational end-over-end or axial movement of the retorts (cookers) achieves the agitation.
• Canning in smaller retorts is called batch method.
• The sealed cans usually not more than a few thousand per batch are manually loaded into the retort on trays or in metal baskets.
• The cooking takes place under steam pressure.

Cooling

• Prompt cooling after processing is important and it checks the action of heat on the food and prevents any change in texture and colour.
• In addition, a marked internal pressure exists in the can when it is removed from steam pressure retort and rapid reduction of this internal pressure is ensued by prompt cooling of the cans.
• Cooling is done either by placing the can under showers (Spray) of cold water or by immersing then in a cold-water tank.
• Cooling can also be done by pressure cooling in the retort when the processing is completed.
• The cans should be cooled to an average temperature of 37°C.
• At all times cooling water should be potable and bacteriologically clean.

Can washing

• Can which has been just cooled are dirty and greasy on the outside and are therefore passed through a detergent bath to facilitate subsequent handling, lacquering and labeling.
• This bath is usually composed of soap or sulphonated fatty alcohol.

Outside lacquering, labelling and storage 

• Commercial lacquer or enamel is a coloured varnish containing vegetable resins or synthetic resins.
• Tins after removal from the detergent bath are washed and lacquer may be applied to the outside of the tin to prevent external corrosion, particularly when the cans are estimated for moisture.