I just finished this for submittal to Alaska Magazine, thought I'd share it here too.
Its too long for one post so I broke it into two parts.
I’ve been doing a good bit of research over the last 3 months about storing dry food for my “just in case” cache. I needed to be absolutely sure since my family’s life will be at stake if we ever need it. I’m very glad I did too; otherwise I would have destroyed most of my cache if I’d simply followed what I’d found with a cursory Google search. Storing outside in a shed in Alaska (or other cold climates) is different.
Alaska is particularly vulnerable to interruptions in food delivery from the lower 48, we’re remote and prone to earthquakes, tsunamis, volcanoes, and severe winter storms. Not to mention potential civil disruptions.
Almost all of our food delivery goes through just a few fragile sea ports, mainly Anchorage. In an earthquake bad enough to damage the ports the airport runways will be probably damaged too so air freight is not really an option either, and in any case the sheer food tonnage required couldn’t be done.
FEMA recommends a minimum of 72 hours of food, water, and medicine on hand per person. Other government sources (post-Katrina) recommend 30 days storage per person.
This is also applicable for food storage in remote cabins or people who live way out in the bush.
Food needs to be stored dry in an air & moisture tight container in a dark cool environment. The container also needs to be rodent proof.
The most important factors are; storage temperature, oxygen, water content of the food & the air trapped with it, and finally light – in about that order.
Containers: Regular plastic sacks or food grade HDPE 5/6 gallon buckets are only good for short term storage (<2-3 years) as oxygen will seep through the plastic.
Your best bang for your buck is O2 blocking aluminized food grade mylar bags of at least 5 mil thickness, (7+ mils is recommended). These look like big thick versions of the silver anti-static bags that computer parts come in. Get the ones that need to be heat sealed (you can do it with a clothes iron) ziplock versions don’t seal perfectly.
These bags are not rodent/puncture proof by any means so they’ll need to be protected by placing them inside another container. 5/6 gallon plastic buckets are ideal but rubbermaid type containers will do in a pinch.
#10 (1 gallon) cans are best but they’re relatively expensive vs volume and you need specialized equipment to seal them.
Large glass canning jars could be an alternative, but they’re fragile and they’re transparent (bad), you’d need to make sure the rubber seals would stay good for 10+ years. Personally, I wouldn’t use them.
I guess metal paint cans could also work, but they’ll need to have a enamel lining and your food should be double protected from touching the metal by being inside a plastic bag. I don’t know how well these would seal either. I’ve never heard of anybody ever using metal paint cans.
Temperature: For every ~11 F below 70 degrees the storage life is doubled:
Temp F -- Years
37.6 -- 40
48.4 -- 30
59.2 -- 20
70.0 -- 10
80.8 -- 5
91.6 -- 2.5
So, in this example something with a 10 year standard shelf life stored at 59.2 degrees will last 20 years, something with a 2 year shelf life will last 4 years, etc. Conversely, if stored above 70 they will go bad that much quicker.
Store your food as cool as possible but do not allow it to freeze unless you take strong measures to remove 97% of the container moisture, more on that later.
Oxygen: Air is about 21% oxygen and 78% nitrogen; the remaining 1% is other gasses. Food will oxidize all by itself in its container, eventually using up all the available oxygen – but by that time your food has gone bad (or rancid if it contains any oils/fats).
In addition bulk wheat/flour, rice, beans, etc will almost invariably have insects eggs in it, if not the insects themselves - they’ll eventually die when all the available oxygen has bound to the food but by then they’ll have badly damaged your food, and who wants to eat dead bugs and old bug poop!
Finally, make sure that you buy “washed” wheat/beans/rice/etc to cut down on the numbers of the little buggers to start with; it’ll also prevent dirt and other potential contaminants.
So, at packing time you need to remove as much of the O2 as you can, quickly. There are two techniques used in conjunction that give the best results:
- Purge the container with dry ice (or nitrogen) at packing time. Carbon dioxide is heavier than air and will displace the oxy/nitro atmosphere as it sublimates and fills up the container from the bottom. 4 ounces is enough to displace all the air inside a bucket but we’re looking to purge the air from inside the nooks and crannies of your food and this requires a bit of a flow so we’ll be putting in 6 ounces. Make sure you wear gloves when handling the dry ice; you can easily freeze your skin.
- No matter what you do there’ll still be a little oxygen in the container and inside the food itself that’ll leach out over time so you’ll need to soak this up too. The easiest means to do that is to toss in a middling sized hand warmer inside the container when you seal it.
You can spend more and buy “oxygen absorbers” online, but hand warmers are cheap, readily available, have the same ingredients (plus more salt as a catalyst), are non-toxic, and have a LOT of extra capacity that will remain and continue to scavenge micro O2 leaks over the years.
Get the warmers that have their own water included. Don’t worry about them getting too hot, if you’ve done the dry ice treatment right there won’t be enough oxy in the container to let it get very hot. I you’re feeling paranoid you can wrap the warmer in a paper towel. *
When the bag is sealed after the purging and O2 absorbing you’ll see that the bag will collapse itself hard to the food. This is happening for two reasons: First, you’re binding oxygen to the iron in the hand warmer and lowering the gas pressure inside your bag. Secondly, the food inside the container is actually absorbing the carbon dioxide and is also lowering pressure inside your bag; this does not change the food in any way. Both of these effects result in pulling a partial vacuum in your bag, it also serves as a visual confirmation that you got a good seal.
Anything with fats or oils (including brown rice and nuts) is especially vulnerable to oxidation and hydrolysis , O2 & water removal is critical to long term storage. Look up “Rancidification” if you’re curious.