Naked Science Forum
General Science => General Science => Topic started by: dentstudent on 11/07/2007 14:06:19
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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?
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Vinegar is made from alcohol so maybe that has something to do with it.
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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).
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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?
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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.
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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.
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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!
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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.
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Ok changing it slightly ,how does smoking something like fish or meat preserve it.
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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?
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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...
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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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The old ones are the best ones! Especially if preserved by the pickling process.
Appropriately enough, this thread seems to have kept well over the ten years since it was last active! Nevertheless, it's an interesting topic and perhaps deserves a re-visit?
We've not really explained why perishables are, well, "perishable", and this lies at the heart of why food "goes off".
Food spoilage is the consequence of chemical reactions and microbial activity. When leaves fall to the ground in the garden, fungi and bacteria pounce and begin to attack the tissue to liberate nutrients, which they use themselves and also redistribute to other elements in the food-chain, including the very plants that made the leaves in the first place.
The same processes happen in the average home larder; fungal spores drifting around in the air land on food and begin to grow a fungal mycelium (a network of fungal threads that grow and ramify through the food). The fungus actively secretes digestive acids, lipid-degrading components and enzymes into the food. These break down cells and reduce their constituents to chemical "rubble" that is carted off by the fungus for recycling. Bacteria arriving in the same way also share in the banquet, helping themselves to the the spoils of the fungal efforts and sometimes contributing nasty heat-resistant toxins that can make you ill if you eat them.
Pickling things in vinegar does several things: one, it excludes an air supply and restricts further access to the food by microbes. Second, the low pH (acidic environment) and high salt content in the vinegar suppress the growth of the majority of microbes, and particularly the ones that cause food to rot or produce harmful toxins. Third, the acid in the vinegar denatures enzymes, including those present in the foodstuff itself, that cause cells and tissues to break down. These includes enzymes like lysozymes. These are released when an apple is "bruised", turning the flesh brown as it breaks itself down. By inhibiting these enzymes you prevent this from happening.
So as you are packing and unpacking your preserves this Christmas, consider that you have chemistry, and the natural antimicrobial effect of acids and salt, to thank for the fine flavour of your pickled onions!
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and high salt content in the vinegar
The salt content of vinegar is practically nil.
Pickle recipes like this one
https://www.sarsons.co.uk/recipes/pickled-onions
include salt, but the amount is too small to act as a preservative- it's just a flavour.
Incidentally, since it's nearly Xmas, I'm reminded of another way to "pickle" fruit.
https://en.wikipedia.org/wiki/Rumtopf
The alcohol and sugar preserve the fruit, mainly by displacing the water that any bacteria or fungi would need.