How to store food reserves
Technical guide to long-term storage. Mylar bags, PET bottles, glass jars, oxygen absorbers. Methods validated by NASA, USDA and LDS Church studies.
The difference between 1 year and 30 years
A bag of rice in the pantry lasts 1-2 years. The same rice, in airtight packaging with oxygen absorbers, inside a plastic bucket in a cool, dark place, lasts 30+ years without losing nutritional value. The difference between the two scenarios is packaging technique — cheap, simple, easy to learn at home.
3 packaging methods
1. Mylar + O₂ absorbers
Professional standard. Aluminised polyester bags block light, oxygen and moisture. With oxygen absorbers: 30+ years. Cost: ~1 €/5 L bag + 0.15 €/absorber.
For rice, wheat, pulses, oats, powdered milk.
2. PET bottle
Cheap reuse. Washed and dried water or soft drink bottles. With O₂ absorber: 10-20 years. Cost: 0 € (reused).
For rice, wheat, beans, peas. Not for foods with fat (wholemeal flour).
3. Airtight glass jar
Portuguese tradition. Jars with rubber-sealed lids. With O₂ absorber: 5-15 years.
For sugar, salt, seeds, dried fruit. Risk of breakage is the biggest limitation.
Method 1: mylar bags + oxygen absorbers
What you need
- Mylar bags of 5-10 L, minimum thickness 5 mil (0.127 mm). Smaller bag: ~0.80 €. Larger bag: ~1.50 €. Sold in packs of 50-100 online (Amazon.es, AliExpress).
- Oxygen absorbers of 300-500 cc each. ~0.15-0.30 € each. Sold in packs of 100. They must arrive sealed — once opened, they activate.
- Iron or heat sealer.
- Flat board and metal ruler to seal in a straight line.
- Airtight food-grade plastic buckets of 12-25 L with screw-on lid. Leroy Merlin, Bricodepot: 5-10 €.
- Labels + permanent marker.
Step-by-step
- Check moisture. Foods must have <10% moisture. Commercial rice, pasta and pulses already are. If in doubt, spread on a tray and dry for 1 hour at 70°C in the oven.
- Fill the mylar bag. Leave 5-10 cm of margin to seal. Compress gently (shake the bag to settle the contents).
- Add absorbers. 1-2 absorbers of 300 cc per 5 L bag. For 10 L bags, use 2-3. Important: work quickly — do not leave the bag open to the air for more than 10 minutes after opening the absorber pack.
- Expel air and seal. Press the bag to remove air. Place the opening on a flat board. Heat the iron to medium-high temperature. Pass slowly over the opening, pressing with the ruler. It seals in 2-3 seconds.
- Check the seal. Once cool, pull gently to confirm it is firm. If there is a leak, reseal closer in.
- Label. Type of food + date of packaging + weight. In an emergency no one wants to guess what is inside.
- Place in bucket. 4-6 bags of 5 L fit in a 25 L bucket. A closed bucket protects against rodents and falls.
- Store. Cool place (<24°C), dark, dry, off the floor (pallet or shelf).
Visual sign that everything is fine
After 24 hours, the absorbers will have consumed the oxygen inside the bag. The bag becomes visibly "shrunk" against the contents (partial vacuum). If this does not happen, either you had a leak in the seal or the absorbers were dead.
Method 2: reused PET bottles
Advantages and limitations
- Advantage: zero cost (reuses packaging), transparent (you can see contents), stackable.
- Limitation: does not block light (requires dark storage), 10-20 year durability vs 30+ for mylar.
- Works well for: rice, wheat grain, beans, dried peas, lentils, oats.
- Avoid for: flours (compact down), oily dried fruit, any wholemeal food (turns rancid).
Step-by-step
- Wash thoroughly. Water bottles with hot water + bicarbonate of soda. Soft drink bottles need 2 washes (sugar residue). Milk bottles: do not use — fat impregnates the plastic.
- Dry completely. Critical. Any residual moisture = mould. Dry upside down for 24-48 hours, or use a hairdryer.
- Fill. A funnel helps. Tap the bottle on the worktop to settle the grains.
- Add O₂ absorber. 1 absorber of 300 cc per 1.5-2 L bottle.
- Tighten the cap. Firmly. The bottle's original cap works.
- Label and store. In a cardboard box (dark) or closed cupboard.
Method 3: airtight glass jars
When to use
- Coarse salt (traditional glass jars)
- Sugar
- Seeds for sprouting (must remain viable — glass keeps conditions stable)
- Short-term dried fruit (6-12 months)
- Spices
Special care
- Jars with a rubber seal (Le Parfait style) guarantee airtightness. A simple metal lid does not seal well.
- Do not fill to the top — leave 2 cm of air for the absorber.
- Dark place (light degrades). Line with paper or store in a cupboard.
- Risk of breakage: do not store at height, always low. Ideal: bottom shelf of the pantry.
Oxygen absorbers — technical explanation
Oxygen absorbers are small white sachets containing iron powder and salt. When exposed to air, the iron oxidises (rusts), consuming the oxygen in the sealed environment. Within a few hours, the atmosphere in the bag goes from 21% O₂ to <0.1% O₂.
How to choose capacity (cc)
- 1 cc = 1 ml of oxygen absorbed
- 1 L mylar bag: use 100-200 cc
- 5 L mylar bag: use 300-500 cc
- 10 L mylar bag: use 500-1000 cc
- 20 L bucket (with bags inside): additional 2000 cc
- 1.5 L PET bottle: 300 cc
Care when handling
- Absorbers begin to activate as soon as the pack is opened. Work quickly (15 min max) for all the day's bags.
- Leftovers go back into a mylar bag with their own absorber — preserves them.
- They are safe (food-grade, even if accidentally swallowed in small amounts), but do not eat them.
- Iron rusting heats up — they feel warm for a few hours. Normal.
- Do not confuse with silica gel: silica gel is different, it absorbs moisture not oxygen. It is not a substitute.
CRITICAL WARNING: botulism
NEVER store moist foods in oxygen-free packaging
Clostridium botulinum is an anaerobic bacterium (it grows in environments without oxygen) that occurs naturally in soil and in small amounts in almost all foods. Under normal conditions (with oxygen) it is dormant. When placed in an oxygen-free environment with moisture, it multiplies and produces the most dangerous toxin known to science.
Golden rule
- SAFE in mylar + absorbers: foods with <10% moisture. Rice, wheat, pulses, oats, pasta, sugar, salt, powdered milk.
- DANGEROUS in mylar + absorbers: any moist food — cooked rice, soup, fresh vegetables, raw or cooked meat, cheese, fresh fruit, home-canned foods without proper pressure canning.
Signs of contamination in a preserve
- Bulging lid, pops on opening
- Strange or sour smell
- Bubbles, foam or milky appearance
- Abnormal colour
If any of these signs — discard immediately without tasting. Botulinum toxin has no smell or taste. Just 0.1 µg can be fatal.
Safe preserves
- Commercial tins: safe (industrial high-pressure sterilisation).
- Homemade fruit/tomato preserves: water bath is sufficient (high acidity inhibits botulism).
- Homemade meat, fish or low-acid vegetable preserves: require pressure canning (special pressure cooker at 116°C+ for a defined time). A simple water bath is NOT sufficient.
Storage location
✓ Good locations
- Interior pantry (north wall)
- Basement (if dry, <24°C)
- Closed cupboard in a corridor
- Storage room without a window
- Under the bed (in flat boxes)
✗ Bad locations
- Loft/attic (very high temperatures in summer)
- Garage in the sun
- Kitchen (variable humidity)
- Bathroom
- Next to heating or boiler
- Directly on the floor (cold + damp)
Defence against rodents and insects
- Plastic buckets with screw-on lids (not press-on lids) — defend against rats.
- Mylar resists puncturing but does not withstand prolonged gnawing. Mylar inside bucket = double defence.
- Bay leaves in the reserves — natural weevil repellent.
- Quarterly inspection of the buckets. Signs of rodents: tooth marks, droppings (1-2 mm black).
- Traps and mousetraps nearby if there is suspicion — without poison (contaminates food).