2

The title says it all. Context: food preservation

  • 4
    Not practical in a home application, so I'm not putting it in an answer; but Irradiation & UV treatment are methods used in commercial preparations. en.wikipedia.org/wiki/Food_irradiation en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation – renesis Nov 18 '15 at 21:15
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    UV-C lamps are available to the general public, both as designated germicidal lamps and as part of EPROM erasers (a gadget electronics techs and enthusiasts use). Two problems: The UV-C actually needs to reach the microbes, so you could only use it on liquids that you could expose to it in very thin layers (probably why the main application is sterilizing juices and equipment surfaces) - and it is really, really harmful to your eyes (the gadget mentioned has a closed chamber and a safety interlock)! – rackandboneman Nov 18 '15 at 22:51
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    Is this just an abstract question or are there particular foods you're actually trying to preserve? – Cascabel Nov 19 '15 at 7:53
7

As Lars Friedrich already wrote, curing with salt is a way to kill bacteria. A high sugar content and the removal of water in general alters the water activity.1
Some chemicals are toxic to bacteria (and to some extend also toxic to humans) like borax (which is used to preserve caviar; I'm not sure if it only inhibits the growth of bacteria) or ethanol (drinking alcohol). Sulfites are used - not exclusively - in wine making and on dried fruit.
You can alter the pH. I doubt the food will be edible as-it-is.
Last but not least you can irradiate the food to sterilize it. Irradiation is also commonly used to sterilize (disposable?) medical equipment.

Please note that freezing does not kill any bacteria.

Side note: There are some other bacteria that survive even in such adverse environments but they are not common as foodborne pathogens. If you really want to be sure that the food is sterile without cooking, you have pressure-sterilize, "poison" it or irradiate it.
You can also preserve food even with bacteria and fungi: A sourdough has an almost indefinitely shelf-live. It basically only consists of flour, water and a mix of many different bacteria and yeasts. Cultured milk also has a very long shelf life.
For further reading: The FAT TOM rule describes the six favorable conditions required for the growth of foodborne pathogens.


1 Caveat: (Botulinum) spores survive in honey. Do they count as bacteria?

  • While everything you say is true, most of it is an answer to a different question. This was about killing bacteria, and you are talking about preventing them from multiplying long-term. Culturing and FAT TOM are not really applicable, and I am not sure that pH counts - if it does, it will be at a different range than the range typically used for preservation. – rumtscho Nov 18 '15 at 22:35
  • @rumtscho: Regarding the acid I rather had balsamic vinegar in mind. I'll edit the "preserving food" out since pure vinegar itself doesn't really count as food. Does drying food only inhibit growth of bacteria but not killing these? – Ching Chong Nov 18 '15 at 23:04
  • The last three paragraph were actually meant as side notes. – Ching Chong Nov 18 '15 at 23:11
  • Thanks for editing, I removed the dv. It's a somewhat blurry case. Usually, giving more relevant information is great, especially when it seems that the OP does not know it. But many people don't even realize that killing bacteria and preventing new growth are two different concerns, and I felt that the old version of your post promoted this misunderstanding. It will be even better if we make a different question listing all preservation methods, where your "side notes" can go, and keep this one about the actual reduction of existing bacterial load. – rumtscho Nov 19 '15 at 0:21
  • Your answer helps a lot @ChingChong. Sugar and salt and the removal of water made me think: would drying food somehow be in the same category (i.e.: removal of water)? – nlambert Nov 19 '15 at 15:15
4

The most common method to kill bacteria without heat is curing with salt. The removal of the water and the addition of salt leads to an osmotic pressure that draws the water out of the bacteria.

  • This is essentially how beef jerky is made: add salt, remove water. – user21524 Nov 19 '15 at 1:28
4

The term is "cold sterilization"; most methods will indeed be out of reach of home users. Some of the methods used in industry seem to be just sieving the bacteria out (microfiltration), pressurizing everything to 50000 psi, or obviously chemicals that remain in the food as preservatives or that self-decompose into relatively inert compounds in storage (Dimethyldicarbonate). Some compounds in common seasonings (Turmeric, Onions/Garlic, Chilies) are claimed to have an effect that lowers bacterial growth (but does not completely inhibit it).

  • Interesting side note: Benzoic compounds, usually considered synthetic preservatives, naturally occur in some dark fruit. – rackandboneman Nov 18 '15 at 22:42
1

Classic sour pickles actually contain a very small amount of salt -- just enough to discourage most bacteria and encourage the growth of Lactobacillus acidophilus. LBA's byproducts then kill off whatever else was trying to compete with it.

Vinegar pickles likewise are a hostile environment for most organisms.

(Folks not too much younger than me can remember when stores had barrels of pickles and you'd just grab the ones you wanted with a pair of tongs. No refrigeration needed.)

Other folks have covered other traditional ways of preserving food -- drying, smoking, etc. A properly cured ham can hang on a hook for years and still be edible, though you may need to trim off the moldy outer surface.

While we're speaking of mold: cheese is another food protected by curing, using various cultures. And again, if you don't mind trimming off the rind, many hard cheeses can pretty much look after themselves.

So can butter, actually -- it may go rancid due to chemical breakdown if not kept cool, but other than that it doesn't need to be refrigerated. Ditto most oils. Ditto most fruit; it may get moldy or start to ferment due to harmless organisms, but otherwise can look after itself longer than most Americans think it can.

1

Certain viruses can be used:

In the Federal Register of August 18, 2006, FDA announced that it had approved the use of a bacteriophage preparation made from six individually purified phages to be used on RTE meat and poultry products as an antimicrobial agent against Listeria monocytogenes.

1

In Home-settings; our family do as the following -

For meat => Use Lemons or limes
- Just simply slice the lemons and squeeze it over the meat in a bowl.
- Leave it for 15 minutes or more (can also refrigerated for overnight if you wish to prepare for another day)

For vegetable => Use salt
- In a bowl of water, add some amount of salt
- Then, add vegetable (after cut)
- Leave it for 15 minutes or more

I hope that's what you are looking for. Thanks.

0

Hydrogen peroxide (H2O2) is used to treat liquids such as milk and stored water. Only a couple of drops of 3-7% aqueous solution of H2O2 in 1L of liquid is enough to disinfect. Fresh milk could last 2 weeks easily when treated.

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