A Beginners Guide to Desiccants

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Packets of SeedsThe concept of using desiccants has always been a bit confusing to me.  Conceptually, I knew what they were, namely little packets of gel  that are packaged with electronic gizmos, new shoes, pill bottles and even clothing purchased over the internet.  I also knew that  many articles, books and websites with information about long term food storage also talked about desiccants.

But what are they?  How are they used?  And are they really necessary?  It seems that depending upon who you consult, they are absolutely 100% necessary or a waste of time and money.  Talk about being confused.  Still, about three months ago I started saving all of those little packets thinking that at some point, I would try to figure out what to do with them and why.

What is a Desiccant?

Starting with its most basic definition, a desiccant is is a substance that absorbs water. It is most commonly used to remove humidity that would normally degrade or even destroy products sensitive to moisture.

Okay. Now I get it.  As an oxygen absorber is to air, a desiccant is to moisture. That means, if I understand correctly, items that may be subject to mold and mildew if left unprotected in a damp area will be safe from those nasties if stored with a little desiccant packet on board.

There are many types of desiccants.  Wikipedia has a fairly lengthy list of desiccants but instead of burdening myself with figuring them out on my own, I asked my friend Ron Brown to share his knowledge of desiccants as well as the results of his experiments using various types of this magical stuff.

silicagel 2

Here is some of what he shared with me.

Some Common and Not So Common Desiccants

silicagel 1Silica Gel:  Silica gel is one of the more common desiccants.  Crafty types use it to dry flowers and in other projects.  As with other desiccants, as water evaporates from the flowers, it’s soaked up by the gel, thus drying them out for posterity.  Packets of silica gel are also found packaged with pills, over the counter remedies and vitamins.  What many people do not know is that these can be reused if you dry them out using low heat in the oven.

Salt:  Salt is a desiccant. If it cakes in the shaker and won’t come out, that means it’s soaked up moisture from the air and the little grains of salt have glued themselves together. To prevent caking, calcium silicate is added to table salt.

Rice:  Rice is added to salt shakers to keep the salt flowing freely. So if salt is a desiccant, maybe rice is an even stronger desiccant.

Calcium Chloride:  Ron indicates that he totally ruined a pair of leather shoes once, spreading calcium chloride with a shovel off the back of a flat-bed truck (to minimize the blowing dust) back in his college-student, summer-job, road-construction days.

Cement and plaster of Paris:  Both cement and plaster of Paris are “calcined” at high temperature and will gradually harden if left setting around the in the garage. They absorb moisture from the air. They are desiccants.

Powdered Non-Dairy Creamer:  A bowl of powdered non-dairy creamer will gradually harden if left on the table unused.  Yes, scary as this sounds, non-dairy creamer is a desiccant.

Plasterboard or Wallboard:  Ever heard of a Kearney fallout meter?  When building a Kearny fallout meter to detect radiation – a topic for another day – you must have a desiccant in the cell to keep the atmosphere as dry as possible. Kearny himself recommended a piece of wallboard or plasterboard that has been broken into half-inch cubes and dried in the oven.

So Which Desiccant is Right For You?

Now here is where things get interesting. Ron ran some experiments testing various types of desiccants and was kind enough to share the results and a tip for making your own desiccant packets below – in his words.

So which desiccant is best?

To answer that question, I took one cup each of silica gel, salt, rice, calcium chloride, plaster of Paris, and non-dairy creamer, poured them in separate bowls, then lined the bowls up on a table in the cellar. Relative humidity was in the 65-75% range. I weighed them in the beginning, gross and tare, and at the end of 40 days.


And the winner is . . .  Calcium chloride!

The net start weight of the calcium chloride – CaCl2 – was 224 grams. The net finished weight was 349 grams. So one cup of calcium chloride picked up 125 grams of water in 40 days, a gain of 56%. (It also doubled in volume.)

CaCl2 - after

The non-dairy creamer was first runner-up. One cup of non-dairy creamer picked up 20 grams of water, an increase of 16%.

None of the others (including the store-bought silica gel) picked up enough moisture in 40 days to measure. The silica gel had a net start weight of 225 grams and an end weight of 225 grams. That’s for 40 days. No doubt a year would tell a different story.

Even so, calcium chloride was the clear winner. Please note that a hard, half-inch thick crust had formed over the surface of the calcium chloride. The crust was almost like concrete, really quite difficult to chip away without breaking the dish.

So where can you buy calcium chloride? One place is in with the canning supplies, sold by Ball as “Pickle Crisp Granules” (5.5 oz. for $6). It makes the pickles crunchy and is used in commercial dills (Claussen, for example).

CaCl2 1

It’s cheaper to buy Morton Safe-T-Power ice melter in plastic cans, 9 lbs. for $5. People use it on their outside steps and sidewalks in winter to melt ice. If you buy pallets of calcium chloride in 50-lb. bags, you can get it for $12 a bag. Tractor-trailer loads are even less.

I put “packets” of desiccant in with my vegetable seeds.

packet type 1

I make the packets from coffee filters (Mr. Coffee-type), cutting, folding, and stapling as necessary. Don’t forget that calcium chloride can potentially double in volume from its original (dry) size. So don’t stuff the packets. More is not better.

Were I to use larger containers – 5-gallon buckets, say, or 30-gallon trash cans – for storing grains, flour, and the like, then I would not use fragile coffee-filter packets. I would use old vitamin bottles or mayonnaise jars (of whatever size seemed appropriate for the task at hand) with many small holes punched in the lid. Jars LABELED with what’s inside, thank you!

packet type 2

But whatever desiccant you choose and however you use it, it is crucial to the success of your storage program. Crucial, critical, important, essential, indispensable, all that stuff.

The Final Word

Clearly, we need a desiccant to put in with the vegetable seeds we’re storing for next year.  It also seems to me that it might not be a bad idea to include a desiccant in with the grain we hope to store for decades.  After all, who wants to go through the time and expense of storing grains for the long term only to have it get smelly, damp and moldy and further, making you sick when you eat it.

I would like to thank Ron for his help in educating me and also for generously sharing his experiment and as well as his method for creating DIY desiccant packets using coffee filters and a bit Calcium chloride or non-dairy coffee creamer.  Seems to me that the next task at hand is to ask him to show us how – in pictures – to build a Kearny fallout meter.

I would also like to put in a plug for Ron, who is the author of  Lanterns, Lamps & Candles.  This e-book on CD is a comprehensive handbook of non-electric lighting.  I have no financial interest in the product (no commissions or anything), just a huge fan of both the CD and Ron!

Enjoy your next adventure through common sense and thoughtful preparation!


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Bargain Bin: Thinking of making up your own packets of desiccants?  Here are some of the product that will get you started.

Ball Pickle Crisp 5.5 oz. Jar: You can make up a large batch of desiccant packets with this tub of “pickle crisp” and some coffee filters such as the Brew Rite #4 Cone Coffee Filters.

DampRid Hi-Capacity Moisture Absorber, 4-Pound TubThis is Calcium Chloride. This stuff has been used by boaters for years and is a popular item.  Seems to me that a 4 pound tube, used to make desiccant packets, would like forever.

Dry-Packs 3gm Cotton Silica Gel Packet, Pack of 20:  These premade packets of silica gel can absorb 40-percent of its weight in water vapor.   There are also these larger packets Dry-Packs 1-Ounce Moisture Absorbing Silica Gel.

20 – 300cc Oxygen Absorbers for Dried Dehydrated Food and Emergency Long Term Food StorageEven if you choose to take a pass on desiccants, oxygen absorbers are a must for preserving bulk foods and grains for ling term storage.

Zwipes Microfiber Cleaning Cloths, 36-Pack:  Thought I might remind you that microfiber cleaning cloths aka magic rags are my absolute favorite for cleaning. Although machine washable and dryable, sometimes I simply hand wash the cloth I am currently using and let it hang to dry.  I use the an napkins when eating and as a bib when I want to protect my clothes from messy spills.  I love these things – I just wish they would wear out so I could get some new ones in different colors.

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Want to try something different?  How about some Freeze Dried Banana Dices?

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A Beginners Guide to Desiccants — 17 Comments

  1. Thanks to Gaye & Ron for such a great article! I knew basically what desiccants were and what they were used for, but had never gone the extra step to what I needed to do with them.

  2. Great simple explanation of desiccants. Proper protection from moisture is important. To that end, combining our moisture barrier bags with a desiccant is one of the most efficient ways to protect your goods. No matter how effective a moisture barrier bag may be, there is always a possibility that a minute amount of moisture may seep in. The use of desiccants is a smart preventive measure for added protection.

  3. Gaye,
    Wow the timing for this article is awesome. We were just discussing this the other day, Thanks again for all you do, and thanks for info on this subject as well.

    • @Billy – I do not have personal experience with kitty litter but I did find this on Wikipedia:

      “Silica gel is also used as cat litter by itself or in combination with more traditional materials, such as clays including bentonite. It is trackless and virtually odorless. Purchasing silica in the form of cat litter can be an easy and cost effective way for retail consumers to purchase silica gel for use in other applications, such as maintaining the desired relative humidity in humidors, keeping tools or other materials rust-free in damp environments or long-term storage, and preserving dried food.”

      So I would say yes.

      — Gaye

  4. Desiccants adsorb water, not absorb water. This mechanism occurs on the surface of the materials, so you really did not need an entire cup when less material could have achieved the equivalent in surface area. Moreover, you did not account and report for the desorption of water in your cellar over the 40 days.

    • Dude, the adsorbtion occurs on a molecular level.. That means that the water molecules sit on the surface of the dessicant MOLECULES, not the surface of the pieces visible to the human eye. For the casual observer who isn’t using an electron microscope it would appear to be absorbed. For goodness sakes has anyone ever taken chemistry ?

  5. Thank you! Great article! So I should use coffee creamer inside coffee filters to save seeds? I am just learning all this stuff. Late getting on board prepping and trying to catch up with the world. thanks!

  6. Hi I realize this is an old article, but as a reference I thought I would mention this:

    DampRid is effective, but every time I’ve used it, in any application, it pulls and pools water. In other words, you have to leave it in a dish or etc. because very quickly you will have a dish full of water which needs to be poured off.

    So, while I find this to be a great product for very humid places like under the sink or in a closet, where I can check the container frequently and empty the water, I think this would be a terrible product for uses such as storing clothing or other goods, where you wouldn’t be able to easily or regularly check and empty out any collected liquid water.

  7. “Silica gel is a partially dehydrated form of polymeric colloidal silicic acid. Silica gel has an amorphous micro-porous structure with a distribution of pore opening sizes of roughly 3-60 angstroms. These interconnected pores form a vast surface area that will attract and hold water by adsorption and capillary condensation, allowing silica gel to adsorb up to 40% of its weight in water. Silica gel is extremely efficient at temperatures below 77°F (25°C) (see Figures 1 and 2), but will lose some of its adsorbing capacity as temperatures begin to rise, much like clay (Figure 3). Much of silica gel’s popularity is due to its non-corrosive, nontoxic nature and its having received US government approval for use in food and drug packaging.”

    Salt will be an excellent electrolyte for any free water and accelerate corrosion and galvanic activity…..

  8. And yet another application for sodium chloride: I would like to add it to my handcrafted potpourri to keep the botanicals crisp. In this application would it be best freely sprinkled into the potpourri mixture. Any guess at what rate?

  9. Boom! Had Ball calcium chloride in the pantry. Made some squares of cloth out of some old sheets about 12″ X 12″. Placed the cloth in a bowl. Emptied a container of calcium chloride onto the cloth. Bundled the cloth up and secured with a zip tie. 3 desiccants in 5 minutes. Placed each desiccant on top of an old plastic lid. Thanks!

    When using a calcium chloride desiccant do not allow it to touch any metal. Calcium chloride is very corrosive! Ask any farmer with water weighted tractor tires where calcium chloride is used as a anti freeze…many a rim has been rusted clean through by calcium chloride.

    Melissa, I don’t know the rate but I run a guest house and make sachets using a technique above. I’m thinking that a sachet made with come calcium chloride and potpourri might be useful in a entry way closet where damp cloths might be hung or perhaps a bathroom or kitchen under the sink to freshen and remove excess moisture. Just remember the corrosive nature of this compound.

    • Perhaps in some specialized applications but not within the context of what we are describing in this article. Definitely not when it comes to food storage, as an example.

  10. This article doesn’t seem to factor in the water already present in the tested materials.

    For example, the rice was very likely not manufactured in a facility that was very stringent with moisture controls. It was dehydrated to a level suitable for safe long-term storage, and nothing more. Further, while shipping and selling to you, it was likely not in a watertight package. And prior to using it for this experiment, had said packaging been opened or accessed for other uses, thus exposing it to moist open-air?

    As far as we can tell, there was already plenty of water in the materials not specifically prepared and packaged for the absorption of water from the air. The results of this test then? Quite inconclusive.

    I can tell you that if you were to take a cup of rice and heat it (much like it was suggested for the silica gel packets) in the oven or even microwave, the rice will come out quite a bit drier than when you put it in. While I don’t have a scale accurate enough to measure the weight, I would invite someone else to do so.

    I typically take about two cups of rice, microwave it for about two minutes (it will get VERY hot, don’t use a plastic dish or it may melt) stir it, and repeat for a total of about eight minutes. The first time I mix it, it sticks to the dish because it’s cooking in the moisture that’s already present. By the second stirring, it will start to release from the dish, shrink, and grow a more opaque white. By the third and final mixing, it’s extremely hot and releasing steam. Even at this point, there is still some water being released. To test this, place the hot rice in a sealed plastic baggie (you might want to wrap it in a paper towel so the bag doesn’t melt), and watch how quickly and thoroughly it fogs up.

    I would very much love to see a test that accounts for this factor, as it is in my opinions, one of the very biggest factors to water absorption – prior water content.


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