Naked Science Forum
General Science => General Science => Topic started by: neilep on 16/08/2006 21:03:45
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Dear Experts On Everything I Am Not (that about covers everything)
We've all seen those scenes when someone opens a tin of food after a hundred years or so !! (well..I have anyway)...
Now assuming the integrity of the tin is never compromised ......
.........is it realistic to accept that food in these tins will remain edible for a hundred years?..a thousand years....forever ?
If not...why not ?...and what happens to tinned food after a hunderd years or so ?
Open up my head with a head-opener and plant some facts in there will ya ?
Ta
Men are the same as women, just inside out !
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I was always told that the first thing to look for is if the tin is bulging, since that means there is some biological process inside, and thus bacterial growth.
Beyond that, tins 100 years old did not have any plastic lining, and so the inner later of metal will have dissolved into the food. Even in the absence of that, I can well imagine that the food itself will have undergone all sorts of changes that, even if it did not make the food dangerous, would probably make it unpalatable – the exact nature of those changes will depend upon what the food is.
George
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Depends on the food. certains types of food last for ages but 100 years is asking alot.
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THANKS GEORGE AND THANKS STEVEN.
I suppose I was thinking that perhaps there was more longevity than the use by date on a tin of food. Some of them are quite literally a few years ahead. I thought because they are hermetically sealed and in a vacuum that as long as the tin was void of cracks and flaws that the edibility factor would be much much longer than the use by dates.
Men are the same as women, just inside out !
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quote:
Originally posted by neilep
I suppose I was thinking that perhaps there was more longevity than the use by date on a tin of food. Some of them are quite literally a few years ahead. I thought because they are hermetically sealed and in a vacuum that as long as the tin was void of cracks and flaws that the edibility factor would be much much longer than the use by dates.
This will depend very much on the food, but personally I don't think the use by dates on tins should be regarded as absolute (in fact, they are rarely absolute on anything).
They are hermetically sealed, but they are not in a vacuum – you don't hear a small implosion when you first puncture a tin. I would guess that they are probably in a low oxygen environment, since the low level of oxygen would be low enough to inhibit the growth of aerobic bacteria, while high enough to remain toxic to anaerobic bacteria – the must worrying of which tends to be botulism (which thrives in anaerobic conditions, and used to be a problem with tinned fish, etc.).
George
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Well I have a bit of experience in this department, Not scientific, but1rst hand knowledge about shelf life so to speak! I have had food storage that has held the test of time to the 2o year mark and the food was still very good. Not A recomended way, but in times of trouble we reverted to our food storage as I had a 1 year supply of food for my family. Much of it was 20 + years old. You must maintain safe conditions heat cold damp etc add to or take away from life. There were a few exceptions. We were able to still open and eat apple butter that had been canned at home a bit over 20 years pryor with no ill effects and it was quite good. There were those things like homemade canned pickles however they did not fair so well.Most of the canned things were good. Watch out for the black errosion on the outside of the can. we found this to be a sure sign that the product inside was acidic and no longer safe!! These food items were carrots tomatoes, beans green and other, corn,hommony, and many other goodies. some of the jams had not made a good seal and over time were ruined. most were fie, the jams were home made in get ths 1968 and The canned stuff lasts a long time, but watch out for corrosion on the can!!Thru 1972. We were eating them through 2005. I stii have some plums and Jam I think, havent been out there to look in about 8 months. These supplies saved our bacon for a year when the hubby lost his job and would not go back to work! Jeesh I thought I was going to strangle him as we had all three kids andages 7 to 13. It was scarey, but thank goodness we had food storage!!I do not know what I would have done without it as I was working taking care of twelve children and my own 3. I was sewing on the side and making crafts for crafts fairs to make ends meet! Hubby was repairing an occassional typewriter when the opotunity arrived. I guess he was taking a break from responsibility and whatever. I never understood!! Still don't. Just be carefull and always remember your eyes and nose are your best friend, then your tongue!!! LOL!
Karen
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I am curious about food items/condiments in plastic? Does anyone know how long Ketchup or Mustard would last ? I know there is an expiration date...but is that an absolute?
"Lo" Loretta
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Mustard lasts a long time. for some reason ketchup not as long. unopened that is. Still lasts a long while. I keep all my food storage about 1 year and then begin using it and replacing it with new as I use it, so that there is fresh! in storage, that is how they recomend it at church!
Karen
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Karen...I remain truly amazed at the things you come out with !!..THANK YOU so much for your very interesting account.
Men are the same as women, just inside out !
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I think I read somewhere that honey lasts for a long time. Unsure, think I'll try and check up on it.
-Steven
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quote:
Originally posted by Mjhavok
I think I read somewhere that honey lasts for a long time. Unsure, think I'll try and check up on it.
-Steven
I think you're right there Steven...I think it must have something to do with the very high sugar content....
Men are the same as women, just inside out !
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quote:
Originally posted by neilep
I think you're right there Steven...I think it must have something to do with the very high sugar content....
Does this mean that if I have a very high sugar content, I too will last a very long time [:D]
George
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This (I mean the honey, the sugar content...) has little to do with the lifespan of canned goods. And it is in the field of food technology, a field I was only indriectly involved with.
The resistance to fermentation, mould formation and lots of other types of degradation is related to the amount of free water.
Sugar and salt are typically products with a high water-binding power, that's why they have been used for ages for the conservations of foodstuffs. They make sure that there is no water available for the growth of bacteria, fungi or whatever.
Canning foodstuffs is first reducing biological activity by a heath treatment (sterilization) followed by closing off all air (air does contain germs).
The main possible reasons for canned goods turning bad are
1)insufficient sterilization (which will cause the bulging tins due to the gas produced in the fermentation proces and
2)corrosion of the tin either from the inside (due to accidity of the foodstoff involved) or from the outside (mere rusting). This may allow air and germs to get into the product inside.
The plastic coated tins we currently have now offer increased resistance to corrosion.
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That seems to be pretty accurate according to what I have experienced with canned goods, and I am no expert! Just had opportunity so live like a popper for awhile!!!LOL Thanks Eric!
Karen