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Author Topic: Is it dangerous to store food in an opened tin?  (Read 23997 times)

Offline Tyron

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Is it dangerous to store food in an opened tin?
« on: 19/01/2011 17:30:03 »
Tyron  asked the Naked Scientists:
   
Hi,

Would leaving food in an opened tin can, make it go off or become poisonous quicker than transferring it to a glass bowl?  
 
many thanks, from a big fan of you guys!
 
Tyron Crowe
South Africa

What do you think?
« Last Edit: 19/01/2011 17:30:03 by _system »


 

Offline CliffordK

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Is it dangerous to store food in an opened tin?
« Reply #1 on: 19/01/2011 20:09:00 »
The inside of a can is sterile.
The outside of it is not, but that effect would be minimal.

The can should also be reasonably resistant to whatever is inside of it, although things like tomatoes will eventually eat through the can, but storing them a few days in a refrigerator is no worse than 6 months in the store.

Iron is good for your diet.  I don't believe that tin is toxic.  Thus, the can itself shouldn't be bad for you.  I suppose recycled metal could have other alloys in it, but the can should be safe.

Anyway, in most cases I wouldn't see any reason to transfer the contents out of a can, especially if you can close it tightly.
 

Offline RD

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Is it dangerous to store food in an opened tin?
« Reply #2 on: 19/01/2011 22:56:41 »
The tin coating oxidises rapidly when the can is opened to the air:
 the exposed part of interior of the tin coated can goes black. This black material comes off easily and could taint the food.

Quote
Don't store food in an opened tin can, or re-use empty cans to cook or store food. This is because when a can has been opened and the food is open to the air, the tin from the can might transfer more quickly to the can's contents.
http://www.eatwell.gov.uk/keepingfoodsafe/storing/
« Last Edit: 10/03/2011 17:36:31 by RD »
 

Offline CliffordK

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Is it dangerous to store food in an opened tin?
« Reply #3 on: 20/01/2011 02:29:59 »
From the link above:
This advice doesn't apply to foods sold in cans that have resealable lids, such as golden syrup and cocoa, because these types of food donít react with the can.

So...  my next question was whether tin was good for you...  or bad for you.  One of my multi-vitamins actually contained a small amount of tin.

There is some debate of the necessity of tin, but here is a review of a rat study and autopsy studies.

Rat studies have shown that tin-deficient diets resulted in poor growth, reduced feeding efficiency, hearing loss, and bilateral (male pattern) hair loss.  Tipton and Shafer examined tin in human tissue after accidental deaths.  They noted that tin was found in the aorta, brain, heart, kidney, liver, muscle, ovary, spleen, pancreas, testes, stomach, and uterus, but none was found in the thyroid of any victim, while the prostate, which usually shows no other trace element, had tin.

It also discusses that tin cans have changed over time.  Most now are lacquered inside.

Daily dietary intake
of tin from various food sources is in the 1 - 3 mg range, which is less than 1/10th of the daily intake obtained
years ago before lacquering tin cans, switching to aluminum cans, or, in the more distant past, when tin cups
or tin pans were still in use.  Since bronze contains copper and tin, the use of tin has been established well
past the Bronze Age, several thousand years ago.

Mutagenic studies on metallic tin and its compounds have been negative. Long-term animal carcinogenic studies have shown fewer malignant tumours in animals exposed to tin than in controls. Human volunteers developed mild signs of toxicity with tin, given in fruit juices, at a concentration of 1400 mg per litre. The WHO 1973 permissible limit for tin in tinned food is 250 micrograms per kg. The adult daily intake of tin was about 17 mg per day in 1940, but it has now decreased to about 3.5 mg, due to improvements in technique of tinning with enamel overcoat and crimped lids to minimize exposure to tin and lead solder. This level is well below the level of 5-7 mg per kg body weight shown to give rise to toxic symptoms. Tin deficiency has not been described in man. Amounts in excess of 130 mg per day have been shown to accumulate in liver and kidneys. Many of the organotin compounds are toxic; the most toxic being trimethyltin and triethyltin, which are well absorbed from the gastrointestinal tract. Most of the other alkyl and aryltin compounds are poorly absorbed from the gastrointestinal tract, and are therefore less toxic when given orally than when given parenterally. The main results of toxicity are skin and eye irritation;

So, trimethyltin and triethyltin are bad...
Otherwise it has very low toxicity, and is poorly absorbed.

Modern tin cans are lacquered, and are better than old ones (how old is the British recommendation?)

Acidic foods might dissolve the tin worse than non-acidic foods.

These notes didn't discuss oxidizing and the stability of the lacquer.
 

Offline graham.d

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Is it dangerous to store food in an opened tin?
« Reply #4 on: 20/01/2011 09:12:42 »
Tins of stuff have a coating inside nowadays. I thought it was some sort of plastic though Clifford refers to it as Lacquer. In any case this prevents any reactions with chemicals in the food.
 

Offline RD

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Is it dangerous to store food in an opened tin?
« Reply #5 on: 10/03/2011 17:34:32 »
A combination of acid contents and oxygen from the air have reacted with the tin in this half-used can of grapefruit.



The grey-black material falls off readily, (into the food contents).
http://www.thenakedscientists.com/forum/index.php?topic=36718.msg340639#msg340639
« Last Edit: 10/03/2011 17:43:28 by RD »
 

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Is it dangerous to store food in an opened tin?
« Reply #5 on: 10/03/2011 17:34:32 »

 

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