Oxygen Absorbers and Desiccants: Which One, How Much, and in What Container

An oxygen absorber is iron powder that rusts and eats the oxygen in a sealed container; it protects dry food from rancidity and kills insect eggs. A desiccant is silica gel or clay that holds water vapor; it protects against rust, mold, caking and dead seeds. One removes oxygen, the other removes moisture, and they are not swapped for each other.

The Home Storage Center rule is 300 cc for a gallon of dense dry food (rice, wheat, beans) in a Mylar pouch, PETE bottle or #10 can, and Utah State's is 50 cc per quart and three 500 cc packets per 5-gallon pail. Rounded up to the packets sold, that is 100 cc for a quart jar or 2-liter bottle, 300 cc per gallon and 1500 cc for a 5-gallon liner. Light foods like pasta, oats and freeze-dried need about twice the cc for the same container: 500 cc for a gallon bag, 2000 cc for a 5-gallon liner. More is never a problem.

No, not in the same container: the desiccant pulls the moisture the absorber needs to work, so one starves the other. One packet per job. Dry food sealed once and left alone gets the absorber; a jar you open often, seeds, medications and anything that rusts get the desiccant; sugar and salt get neither.

Sugar, brown sugar, salt and honey (the absorber bricks sugar and does nothing for the rest), anything over about 10 percent moisture such as leathery dried fruit or jerky (botulism risk in low oxygen), and seeds you mean to plant. Oily foods like nuts and brown rice can take one but the oil still goes rancid within about a year.

About 31 g of silica gel per cubic foot of empty space, the military packaging rule. A .50 cal can is about a quarter of a cubic foot, so 10 g is enough and a 40 to 50 g pack just lasts longer between checks; a .30 cal can needs about 5 g. Dry the beads at 200 to 250°F for one to two hours when the indicator changes and put them back.

Minutes in open air: Utah State says use them within 15 minutes, the makers say seal within 30. Leftovers go straight into the smallest glass jar that fits, lid tight, and keep about six months that way. Unopened in the maker's vacuum bag they last six months to a year; a puffy bag means they are spent.

A fresh packet is loose pink or gray powder; a spent one has turned brown and clumped, and a working one feels slightly warm. The real test is the container: a Mylar bag pulls in tight around the food and a jar lid pops down within 24 to 48 hours. If it is still loose on day two, the absorber was dead or the seal leaks.

Not on its own. HDPE lets oxygen through over months, and BYU could not hold a sealed bucket of wheat under 1 percent oxygen. Line the bucket with a foil Mylar bag, put the absorber in the bag and heat seal it; the bucket then does the job it is good at, keeping rodents, light and knocks off the bag.

Plastic formulated and tested so nothing harmful leaches into food, which is a regulatory standard, not a recycling number. HDPE buckets marked food grade with a gasket lid, PETE bottles that held food, and glass are the containers extension services name. A bucket that held paint or chemicals is not food grade whatever its code.

Spread the beads on a sheet pan and hold them at 200 to 250°F for one to two hours, or until indicating beads turn back to orange; never above 325°F or the gel is damaged. Tyvek packets melt at 250°F, so cut them open or stay at 200. Clay regenerates the same way; calcium chloride cannot be regenerated.

Use the orange kind. Blue indicating silica gel is dyed with cobalt chloride, a sensitizer, and the makers say not to use it in contact with food or drugs. Plain white silica gel and orange indicating gel are the food-contact grades.

Dry, low-fat food at about 10 percent moisture or under: white rice, wheat, dry beans, lentils, split peas, rolled oats, pasta, potato flakes, nonfat dry milk, white flour, and freeze-dried or snap-dry dehydrated food you pack yourself. With the right absorber, kept cool and dark, the grains and beans run 25 to 30 years on the Home Storage Center list. Oily food (brown rice, nuts, whole wheat flour) gains months, not decades, and sugar and salt want a dry container with no absorber at all.

5 mil foil laminate is the standard for food. 7 mil adds puncture resistance, 8 mil holds up better to packing and handling, 10 and 12 mil are for sharp or dense loads like pasta and rough handling, and 14 mil and up is industrial grade, more than a pantry needs. Thickness is about handling; the foil layer is what blocks oxygen, so metallized balloon film is out at any thickness.

A clothes iron or a hair straightener on a flat board, or an impulse sealer. Fill, tamp, drop the absorber in last, then make one smooth, continuous seal across the top with no wrinkles or food in the seam; two passes closes any gap the first one left. Leave an inch above the seal so the bag can be cut open and resealed later. The bag should pull in tight within a day or two; a bag still soft on day two gets a new absorber and a new seal.

For a new long-term pantry, in this order: white rice, dry beans, rolled oats, pasta, wheat, then bulk freeze-dried vegetables or meals. They give calories, protein and decades of shelf life with the least fuss, and every one of them takes the standard absorber in a Mylar bag, a jar, a PETE bottle or a bucket liner.

No. A vacuum sealer leaves oxygen behind and plastic bags let more back in over a year or two, so extension services call vacuum sealing a short-term method, not preservation. The Home Storage Center says absorbers remove oxygen more effectively. For moist food, vacuum sealing also raises the botulism risk, so it goes in the freezer or the fridge.