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Offline dentstudent

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« on: 11/07/2007 14:06:19 »
What is it about vinegar that preserves whatever you put into it? Is it just the absence of oxygen? But then, olive oil would do the same. Vinegar is acidic, so why doesn't it just eat away whatever you put in?


 

Offline DoctorBeaver

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« Reply #1 on: 11/07/2007 14:36:50 »
Vinegar is made from alcohol so maybe that has something to do with it.
 

another_someone

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« Reply #2 on: 11/07/2007 15:29:42 »
What is it about vinegar that preserves whatever you put into it? Is it just the absence of oxygen? But then, olive oil would do the same. Vinegar is acidic, so why doesn't it just eat away whatever you put in?

Not all acids are the same - after all, vitamin C is an acid, and so are amino acids.

Vinegar is very good at dissolving the shells from birds eggs (i.e. it will easily dissolve calcium carbonate - and hence is also good at removing limescale).
 

Offline dentstudent

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« Reply #3 on: 11/07/2007 15:35:16 »
Aren't all acids inherently corrosive? But then, I guess alkalis are too? Doc says that vinegar is an alcohol, so what then is the preservative in alcohol, or rather how does it do it?
 

another_someone

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« Reply #4 on: 11/07/2007 19:34:10 »
Aren't all acids inherently corrosive? But then, I guess alkalis are too?

Corrosive against what?

Nor is the corrosive nature of acids themselves necessarily a cause for it to kill an organism.  Bear in mind that our stomachs contain hydrochloric (which is considerably more corrosive, in general terms, than the acetic acid of vinegar), yet not only do we survive this acid, but there are bacteria that thrive in such acidic environments.  What is true is that any organism is adapted to a particular environment, and organisms that are adapted to acidic environments will usually not be happy in anything else, but an organism that is not adapted to an acidic environment will not normally survive a highly acidic environment.  Since most of the outside environment is not very acidic, nor very alkali, so most organisms that live in the outside world are not well adapted to strongly acidic or strongly alkali environments.

As for the corrosive nature of acids, although some acids have milder than others, but even within that spectrum, some acids will attack some materials but not others, while a different acid might do the converse.

Maybe one of the chemists would like to come along and give a clearer explanation of that (I know some of the reasons this might be, but I don't claim to have the overall picture as to what all the variables are).

I would move this over to the chemistry section, but then maybe the biologists would miss out on the other bits that are more pertinent to the original question.

Doc says that vinegar is an alcohol, so what then is the preservative in alcohol, or rather how does it do it?

No - what he said was that vinegar is made from alcohol - which is not the same thing.
 

Offline Soul Surfer

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« Reply #5 on: 14/07/2007 23:52:09 »
most preservatives just tend to inhibit or kill the bacteria that would otherwise cause the object to decay.  The acids used are relatively weak ones that do not destroy the structure of the material very quickly.  Alcohol and formaldehyde are also used to preserve organic samples but are not really suitable for things that are to be eaten.  Oils can be used to exclude air  but the most common preservative is just to heat the item to kill all the bacteria and then seal it in a container like canning or bottling.
 

Offline that mad man

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« Reply #6 on: 15/07/2007 19:42:10 »
Aren't all acids inherently corrosive? But then, I guess alkalis are too? Doc says that vinegar is an alcohol, so what then is the preservative in alcohol, or rather how does it do it?


Proper vinegar is traditionally brewed from malt, the alcohol brew then gets converted into Vinegar and is no longer alcoholic. You can get "chip shop" vinegar which is just acetic acid and some colouring and as its not "brewed" its acceptable to Muslims.


The worst thing that can happen in home brewing of wine or beer is that the brew can get infected by a fruit fly, "Drosophila". They are attracted to the smell of the brew and once infected it turns it to vinegar.

Ok if you want some nice wine vinegar with taste!

 

Online Bored chemist

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« Reply #7 on: 15/07/2007 20:00:34 »
It's not the fly that turns the wine to vinegar, it's the bacteria they carry.
http://www.vinegarman.com/zoo_vinegar_bacteria1.shtml

There are a few organic acids used as preservatives. Vinegar is the best known but benzoic acid and sorbic acid get used too. Part of their action relies on them being acids but there is some other specific effect on (at least some) bacteria because they work better than mineral acids. Since vinegar is 95% water and the small ammount of acetic acid it contains isn't a strong acid anyway it isn't very corrosive.
Alcohol also acts as a preservative, at least in part because life is generally adapted to work well in water and replacing some of the water by something else (like alcohol) upsets all the chemistry on which the life depends. In effect pickling something in alcohol is drying it.
 

Offline ukmicky

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« Reply #8 on: 15/07/2007 21:34:16 »
Ok changing it slightly ,how does smoking something like fish or meat preserve it.
 

Offline that mad man

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« Reply #9 on: 16/07/2007 00:16:26 »
It's not the fly that turns the wine to vinegar, it's the bacteria they carry.


That's why I mentioned infected.  ;)

Not sure how they do it commercially, maybe add a bacteria culture at some stage?
 

Offline lightarrow

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« Reply #10 on: 16/07/2007 08:36:14 »
Ok changing it slightly ,how does smoking something like fish or meat preserve it.
Because that smoke contains high concentrations of toxic substances for bacteria, produced by the incomplete combustion. So, if you think that smoking cigarettes can disinfect your lungs, you're right. Unfortunately, those same substances are also carcinogenic for us...
 

paul.fr

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« Reply #11 on: 16/07/2007 22:30:11 »
Ok changing it slightly ,how does smoking something like fish or meat preserve it.

Smoking meat (such as ham), is when it is hung in a smokehouse and allowed to absorb smoke from smoldering fires. serving to dry cure the pork and slow the development of rancidity.
In the dry cure technique, ham is rubbed with the dry curing mixture (salt and sodium nitrate) and allowed to stand until the meat is permeated. Salt will only penetrate the meat in the form of liquid brine. Dry salt forms brine when it comes in contact with the natural juice of the ham
 

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« Reply #11 on: 16/07/2007 22:30:11 »

 

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