It seems to be the 'in' thing now days among the Internet crowd to throw a desiccant packet or two into their food storage container before putting on the lid. Here at Walton Feed we don't do this, now let me tell you why.
Desiccant packs won't even start to get this job done. Let me explain: First, let's do the math. For the bean/grain seeds I've checked, the specific gravity is between 1.0 and 1.2. As water has a specific gravity of 1.0 we can use the weight of the seeds themselves to determine how much water is in the seeds at a given moisture content.
Let's use a 6 gallon bucket of wheat with a 15% moisture content for our example. The wheat weighs 45 lbs. To figure how much water by weight is in this sized sample, multiply the weight of the wheat by it's water content. So let's figure it: 45 lbs X 15%=6.75 lbs of water. But we only want to remove 1/3 of this water, (6.75 X 0.33=2.23 pounds of water) or about 2 1/4 lbs water as we don't want to take out all of the water, but rather only bring it down to a 10% moisture level. As one cup of water weighs 1/2 lb, that 2 1/4 lbs of water has a volume measurement of 4.5 cups water (just a bit over 1 Liter). Good, dry desiccant can absorb 40% it's weight in moisture. To absorb this much water you'd need at least 6 lbs of desiccant.
Now, there's no way that a small moisture absorber packet, or several for that matter, are going to remove that much water.
Suzanne Ashworth in her book, Seed to Seed, explains the right way of how to do this using desiccant. "...Color indicating silica gel is an excellent "desiccant" (moisture absorbing material) for drying seeds... The [silica gel] beads are deep blue when completely dry, but gradually change to light pink as moisture is absorbed... The drying process requires a glass jar with an airtight lid... Determine the total weight of the seeds and packets, and then measure out an equal weight of dark blue silica gel. Place both the packets [of seeds] and silica gel into the jar and screw the lid on tightly. The silica gel will immediately start absorbing moisture from the seeds...
"Both large and small seeds reach optimum moisture levels for storage after seven or eight days in the container... Open the container and separate the packets of seeds from the silica gel then repackage the seeds in airtight containers."
Ms. Ashworth suggests using equal parts of seeds and desiccant. This is not practical considering the large amounts of food we are storing at one time. So, what do you do? You don't want to put your food in the oven as this will destroy the storageability of your food. I only know one other way - you have to air dry them. Farmers have big fans that pull outside air into their storage bins and circulate it up through the seeds. The fan goes on when the humidity conditions are low, and is turned off as the humidity rises either because of wet weather or dropping temperatures. Even this isn't really practical for the average person as he doesn't have the equipment. The easiest thing to do is make sure the food you get is already at 10% moisture or less, then pack it up for long term storage before it has a chance to sit around in moist conditions and gain moisture. If you live in a dry climate like we do here in the Intermountain West - Don't Worry!
Let me repeat Geri Guidetti's seed dryness test you can do at home. "...ten percent is good. Don't fret about needing instruments to measure this. Longer seeds should snap smartly, cleanly in half when bent if they are this dry. Wheat and corn seeds should shatter and powder when hit with the head of a hammer (That's the Geri Guidetti Dry Seed Test--you won't find it in a book. It is very reliable, though.) Beans, peas and other large seeds will shatter....Geri Guidetti, Non-hybrid Gardening Forum moderator
Alan T. Hagan in his food storage FAQs also has a way of determining moisture content. Don't confuse his method of checking for seed moisture as an accpetable method for drying your seeds for long term storage, however.
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Revised: 29 Nov 99