Hello Mr. Rawles,
I have a question concerning silica gel desiccant measurements. I have found that buying the desiccant in bulk from flower shops more economical for me, but need assistance with putting together an accurate measurement for 5 or 6 gallon food buckets. On the Alan T. Hagan [Food Storage FAQ] site, he say’s to use coffee filters to make the packets which is a good source and on other vendor sites it say’s that 1500 to 2000 cc’s is to be used for the 5 or 6 gallon bucket’s, my problem is how to measure those amount’s and the others for that matter (300, 500, 750, 1000 cc’s seem to be the usual amounts). I have a kitchen measuring cup and some conversion tables off the net but the amount that is poured seem’s over measured (measured in ml BTW, ml=cc) because it seems quite large (the homemade packets). Any clarification/ help is greatly appreciated. – Derrick
JWR Replies: You are correct that a cubic centimeter is the same volume as a milliliter (mL or ml). 1 cup volume is about 240 to 250 mls. So the 1,500 to 2,000 cc figure does seem very high. At first glance, I think that they might have been off by a factor of 10 when they made their calculations. Typically, what is used for a sealed 5 or 6 gallon bucket of storage rice or wheat is a two ounce (56 gram) packet of silica gel, or perhaps two packets if you live in a damp climate. But let me provide a thoroughly defined answer, since a gram is a unit of weight and a milliliter is a unit of volume. Dry silica gel weighs 680 grams per liter. When it is saturated, it weighs considerably more. But as the basis for our calculations, you can assume that the weight of dry silica gel is .68 of the weight of an equivalent volume of water. Hence:, for Water: 1 cc = 1 ml = 1 gram. (Well, to be absolutely scientifically precise, 1 milliliter equals 1.000028 cc and 1 cc equals 0.999972 ml., but we aren’t splitting atoms here), and for Silica gel: 1 cc = 1 ml = .68 gram. So, 100 grams (about 3.5 ounces) of dry silica gel would occupy a volume of 68 mls, or just over 1/4 of a cup, and 400 grams of dry silica gel would measure just over one cup.
You should always dry your silica gel before using it. This can be accomplished by placing the packets in a home dehydrator (such as the Excalibur brand–highly recommended) for 10 hours, or on a cookie sheet in a kitchen oven set to 150 to 180 degrees for 12 hours. (Make sure that the paper is not close to the heating element.) When dry, (down to around 2% moisture) 1000 grams of silica gel will occupy a volume of about 680 mls or 2-1/4 cups. So the 1,500cc (ml) figure that they mentioned would equate to more than five cups of silica gel! Whoa! We had better move that decimal place over a notch! A half cup (120 ml) of dry silica gel is plenty for a five or 6 gallon bucket.
OBTW, I don’t recommend adding any desiccant to buckets of dried beans. (Although you should add an 02 absorbing packet.) If beans get too dry, it actually shortens their useful shelf life. If they get too dry, then soaking them–even for many days–will not plump them up properly, and they will not be palatable. If you are faced with the “hard bean” problem, you can resort to either using a pressure cooker, or grinding the beans, to salvage them.
The bottom line to all this number crunching is the good news: With the aforementioned exception of beans, there is no such thing as “too much” silica gel in a dried food storage bucket. If you inadvertently use two or three times too much, there is no harm done. But it would be a needless expense unless you can get it in bulk at very low cost or find someone giving it away. As you mentioned, florist shops are a good source. Another source is piano shops. Most of the pianos that are imported from Japan come with a large bag of silica gel. (Usually 600 to 800 grams.) One of those bags is the perfect size to protect the contents of a typical home gun vault.(Be sure to re-dry it once a year, or once per quarter if you live in a damp climate.) If you make some phone calls, these big bags are often available free for the asking–or next to it–if you pick them up at your local piano store.
For those not inclined toward scrounging, commercially-made silica gel packets are available from a variety of Internet vendors such as Ready Made Resources and Nitro-Pak. Both of those vendors also sell oxygen absorbing packets, which are crucial to ensure that insect larvae won’t survive in your food storage buckets.