Vacuum Packing

[PEEDIE]

I've seen some posts on the forum about vacuum packing rations and why some can be stored at room temperature. This is a complicated issue and has some safety implications.

1) Air lets some bacteria grow and this makes food go off quickly. The bacteria that spoil meat, Pseudomonas, need oxygen.
2) Removing air reduces the rate of spoilage of food.
3) Removing oxygen allows anaerobic bacteria to grow. These are bacteria that don't like oxygen.
4) Clostridium botulinum is an anaerobe. It causes botulism.
5) Botulinum toxin is a neurotoxin - it is what is used in botox (BOtulinum TOXin)
6) The type E botulinum toxin is the most toxic naturally occuring material to humans on the planet
7) Vacuum packing can provide an environment that could allow Clostridium botulinum to grow in the right temperature conditions.
8) This could be lethal
9) Ration packs sold commercially have been "terminally sterilised" by heating at at least 121 C for a period that would give a minimum of a 1 in a million chance that in the most extreme case there might be one spore of Clostridium botulinum that would survive.
10) Clostridium botulinum is an organism that is found in soil - like its cousin Clostridium perfringens. This one causes gangrene - and also produces toxins that give spectacular food poisoning.

This sounds all scarey - and it should. Botulinum toxin will paralyse you and you suffocate to death as your diaphram can no longer contract as the nerve impulses no longer make the muscle contract.

This does not mean that you cannot vaccum pack rations, but there are some recommendations I would make.

A) For materials with meat in them, vacuum pack them, but then sterilise the packs in a pressure cooker. This will make them the equivalent of commercial vac-pack rations.
B) the vacuum only holds if the pack remains intact
C) Commercial rations come in laminate packs. These laminates have a polyethylene inner layer and a mylar outer layer. Mylar is a nylon and it's funtion is to protect the soft polyethylene underneath.
D) You will also come across triple laminate packs. These have polyethylene, aluminium, mylar as layers. Polyethylene acts as the sealing material. Aluminium eliminates oxygen and light. Mylar protects the layers beneath it.
E) These typoe of packs were developed for the NASA space programmes, and eventually adopted by the US military. They are lighter, and if you happen to land on one of them you bones don't break - unlike the traditional canned (c-rations).

I'm a microbiologist and a food scientist - just incase your wondering

 

[Toddy]

Does botulism not have a characteristic smell of excrement though?

I'm not naysaying your advice in the least, just that most of us forage and we eat the stuff just as it comes...today I had everything from brambles to bittercress, from reedmace pollen to wild strawberries...and half a dozen other plants that I munched as I weeded the garden, and I washed none of them, and tbh my hands were filthy.
The old phrase about eating a peck of dirt, and all that

How does our immune system manage with the constant low dosage of background bacteria and suchlike ?

I'm an archaeologist, we're supposed to have regular vaccinations against lockjaw, but my reaction to the vaccination was so severe that the Doctor said it was a waste of time.
Does our lifestyle build up and protect us against botulism too ?

cheers,
Toddy

 

[cranmere]

When we eat botulinum spores or bugs fresh our digestive systems deal with it. The problem is that in anaerobic conditions it can grow and produce a toxin and it's that toxin that causes the problems. Our digestive system doesn't break that down. In large quantities yes, it smells, but you only need a tiny amount to kill you. It's worth knowing that honey often has a few spores in it, and babies' digestive systems are not sufficiently strong to destroy the spores which is why it's recommended that you don't give tiny babies raw honey.

Yes, low level exposure in food etc will certainly give you good resistance to a lot of them. There are some exceptions, for example norovirus doesn't produce a strong immune reaction and you need a very small amount of the virus to cause problems. We rarely have any problems when eating out but I've encountered people who are hygiene fanatics and they tend to get upset stomachs very easily.

The immunity you get from either vaccines or the diseases can fade with time but the rate at which it fades is individual and quite variable. If you have a tetanus vaccination while you still have good immunity you will get the sort of reaction you experienced. It probably means that you develop good immunity that doesn't fade as fast as usual.

 

[Teepee]

Pertinent info Peedie, thanks for posting. I'm just starting to pack my diy dried rations in my new vacuum sealer for a 3 weeks walk and the dried meat and veg needs to stay fresh for a month. I'm wondering how moisture levels affect the growth of botulinum?

Raising the vacuum packed meals to 120 c will probably make the polyethylene bag fail which concerns me. Are you suggestting that not vacuum packing would be a better course of action?

 

[Teepee]

Further reading/research on this has suggested from a few sources that Botulinum won't multiply at under 37 DegF and also needs moist food to grow on. My foods are so dry, they snap and crumble

For my personal use of vacuum packing purely dried foods, keeping the packing conditions very clean, using moisture absorbing silica gel packets and storing the meals in the bottom of the fridge til they go in the pack for a maximum of 2 weeks, I believe the risk is negated for practical purposes.

 

[HillBill]

If you put oxygen absorbers and moisture absorbers in to dry foods they should be good.

 

[Teepee]

http://multimedia.food.gov.uk/multimedia/pdfs/publication/vacpacguide.pdf