The main causes of spoilage of canned products are of two types:
i) Microbial spoilage and
ii) Chemical and Physical spoilage.
The spoilage due to microorganisms is of more importance than other spoilage. Spoilage cans exhibit characteristics differences in appearance, taste and odour from normal cans.
1. Swell:
Generally , the ends of a normal and perfect can are flat or slightly concave. A swelled can is one whose ends are slightly bulged due to the formation of gas within the can as a result of decomposition caused by microbial or chemical activity. The end of the swell can remain convex and spring back to this position if pressed inward. The product of the swelled can is not fit for consumption as it may be poisonous because of the presence of bacteria.
2. Hydrogen Swell:
This is caused to the formation of hydrogen and is followed by internal corrosion of the can. The products of such cans are usually harmless for consumption as due to the foods containing organic acids such as fruit and other acid products which corrode the interior of the cans.
3. Springer:
The one end of the can becomes bulged and on pressing or pushing, the other end bulges in the places of preveious one and a can in this condition is known as “Springer”. Springer may be due to the initial stage of hydrogen sweel or by over filling the cans or by insufficient exhausting. Product is fit for consumption.
4. Flipper:
This is due to the mild positive pressure resulted inside the can due to overfilling or under exhausting. The can may be of normal appearance but the end if struck sharply against a solid or table top it becomes convex but it can be pushed back to its normal condition by a little pressure.
5. Flat Sour:
Non-acidic foods like vegetables are spoiled by development of microorganisms without production of gas resulting in flat sour due to presence of higher acidity than normal one. The product is unit for consumption.
6. Leaker:
When a can leaks any part of its contents it is called as “ a leaker”. This type of spoilage is caused due the following reasons:
i) Faulty seaming
ii) Excessive internal pressure due to microbial spoilage or corrosion.
iii) Mechanical damage during handling and
iv) Internal or External corrosion.
7. Breather:
If the pressure guage shows no vacuum inside a can it is called as “ Breather”. An air may pass in and out due to presence of small leak.
8. Bursting of Cans:
This may be due to action on tin plate. Tanning is coming in contact with tin plate and forms black compounds sometimes sulphur di-oxide is formed due to decomposition of proteins and combines with tinplate, resulting information of iron sulphide which is black in colour.
9. Discolouration of Products:
This occurs due to action of acids on tin plate. Tannin coming in contact, with tin plate form back compounds, some times gas of sulphur di-oxide is formed due to composition of proteins. SO2 combines with tinplate resulting information of iron sulphide which is black in colour.
Important Hints:
1. Use can of good quality tin plate.
2. Citric acid up to 0.5 should be added to syrup.
3. Use of canning fruits of low acidity. E.g. mango.
4. Seal the cans when hot (Temperature 165 0F).
5. Leave the proper head space( ¼ inches) before fixing the lid.
6. Cans should be stored under cool and dry conditions.
