Using Dry Ice To Preserve Your Food
Even though oxygen absorbers are easier, I prefer using dry ice to store my foods because it is so much cheaper and as a fumigant it actively kills bugs as well. All one needs is a bucket with a lid that will make an airtight seal and a little dry ice. Dry ice is a solid and looks much like regular ice - except that it's -110 degrees F. below zero (-78.5C). You have to use a lot of caution when handling this product as it will burn your skin if it makes contact.
Actually, dry ice can be a lot of fun. Put a cube in a glass of water and kids will watch the thick cloud that boils off. It will compete with your TV, at least for a while. When I was a kid back in the 50's we used to put dry ice in our home made root beer to make it fizzy.
Dry ice is frozen carbon dioxide. Carbon dioxide is a harmless enough gas as long as it doesn't dissipate all the oxygen in the air you are breathing. Unless you are doing this in an airtight closet, there shouldn't be anything to worry about. But be aware that under unusual circumstances carbon dioxide can kill you. I got an E-mail once from a lady reading this page who said a friend "died while using dry ice during a Halloween haunted house program." Apparently, he was under a card table covered with a blanket, using water and dry ice to make a thick cloud. "It didn't take an airtight closet to kill him," she said. Counter this with the news story of the woman who put a whole tub of dry ice under her husband's bed trying to 'do him in.' When she was arrested for attempted murder she said, "I don't understand, it worked on Matlock!"
We breath in air containing oxygen and breath out air containing carbon dioxide. There's carbon dioxide in our houses all the time simply because we are breathing. I've heard people say you have to do this outside or the fumes will get you. That's the reason I'm making such a big deal out of this. Just use common sense.
Carbon dioxide, in it's frozen form, is highly compressed compared to it's gaseous state. A pound of it contains enough carbon dioxide gas to make 8.3 cubic feet of carbon dioxide gas. A six gallon bucket contains 1.46 cubic feet of space. Fill the bucket full of beans or wheat and you have about 0.48 cubic feet of air left in the container surrounding your food. So, if you use twice as much dry ice as you actually need to displace the air in the bucket, you will need about .06 lbs, or right at one ounce of dry ice. Heck, be generous and put in two ounces of dry ice if you like. The smallest amount of dry ice I can purchase is 5 lbs. which costs me $5.00. At even 2 ounces per bucket, that's enough dry ice to take care of preserving 40 buckets of food, more than I have ever done at one time. At two ounces per bucket, this is enough dry ice to push the air out of a six gallon bucket four times. You want a little bit of overkill or redundancy here as it's always better to overdo this than under-do it and end up with oxygen left in the container. Realize also that this is a purging operation. Even really good purges generally only get out 90% of the air. As air is about 21% oxygen, this would still leave 2% oxygen in your container. You aren't going to get it all out, just most of it.
Where To Get Dry Ice. I get all my dry ice from a welding supply shop. It's also often available at ice cream places and chemical supply houses. When you get your dry ice you need to bring your own container to put it in. There is one thing you really need to watch for if you are going to be using dry ice to preserve your foods. You must prevent water vapor from freezing on the outside of the dry ice. This moisture would later melt off the dry ice in the bottom of your bucket and increase the water content of your dried foods. As you don't often have a lot of room to play with as far as water content is concerned, it is important to ensure you don't add any moisture to your product with your dry ice. The dry ice you buy from the store should be water free, and that's the way you want to keep it.
Dry ice is always giving off carbon dioxide gas, so it's relatively easy to keep the water moisture from it. Just be sure you don't put it into a container that breaths, like a paper bag or cardboard box. I use a Tupperware container which has it's own lid. This container is just right because it's lid is tight enough to keep water vapor from the ambient air out, but loose enough to permit the carbon dioxide gas to escape as it sublimates. By the time you get it home, there will be a thick layer of frost on the outside of the container - exactly where you want it, on the outside - not the inside. The inside will be moisture free because of the continually escaping carbon dioxide gas.
There was one time I purchased dry ice which had a bunch of water crystals mixed in with it. You can tell this because there is a white powder mixed in with the dry ice cubes. Ice is just a tiny bit whiter than the light blue dry ice. You can put a teaspoon or two of this powder in a bowl, wrap plastic wrap around the top, and wait for it to turn into a gas. If it's indeed water, when it melts you will get a little liquid in the bottom of your bowl. If it was 100% dry ice, the bowl will be dry.
You can use dry ice with powders, such as flour, powdered milk, eggs, cheese and things like this. But you need to be a little careful because if you pack it too tightly the expanding carbon dioxide gas will push whatever it is you are packing, up and out the top of the container. I always put the dry ice on the bottom of the container before I add the product. You could put the dry ice on the top of the food when powders are being stored, but this would do nothing to get the oxygen out that is mixed in with the powder. At home I use dry ice to preserve all my seeds. This includes all the grains and legumes. As long as it is a food which air can freely circulate around, dry ice works great. Dry ice will work fine with all the pastas as well.
Before you ever buy it, plan on having your packing operation complete 5-6 hours after you've purchased the dry ice. Otherwise, it may 'sublimate' away on you until it's gone whether you are finished packing your buckets or not.
So, how do you do it?
Materials Needed: A food scale, a measuring cup, dry ice, the food you are planning on preserving, and storage containers.
The process: Zero your food scale with the measuring cup sitting on top of it. Open the container with your dry ice in it and take out about 1/3 cup and measure it. Depending on how your dry ice cubes are shaped, you should have about 2 ounces. (Remember, if you want to be stingy, one ounce will do the trick, that's 28.5 grams.)
Two ounces of dry ice in the bottom of a plastic bucket.
Pour this into the bottom of the bucket in a neat little pile and place a paper towel over the top. Why the paper towel? It keeps the dry ice away from the food, not that it's that important. Now place your product inside the bucket, filling the bucket up to within a 1/2 inch of the top. Set the lid lightly on top and wait. Recently, I have been sealing the lid all the way around except for one small side.
Leave at least part of the lid unsealed until the dry ice has dissipated.
You DO NOT want to seal the lid completely as the carbon dioxide and air must have a place to escape. If the lid makes an airtight seal, the expanding carbon dioxide inside the bucket will continue to increase in pressure until something gives - either the lid will pop off or the bucket will split. Either way you are going to have food all over the place. How do you know when all the dry ice is gone and it's safe to seal the lid? Simply pick up the bucket and feel the bottom. If it is still icy cold there's still dry ice in the bottom. You may need to be a little patient here. My experience has been that it takes 1 to 2 hours for all the dry ice to change into a gas. I've had others E-mail me saying they had to wait around for 5-6 hours! So you may wish to plan in a cerain amount of time for this in case it takes a while. You want to seal the lid just as soon as this has happened, however, because if you don't, air will start circulating back into the container.
After 15 or 20 minutes, I start checking my buckets, and then recheck them every ten minutes or so. After you seal your buckets, it's always a good idea to keep an eye on the lids for the next hour or so. The lids will start bulging up if you sealed them a bit prematurely. If this happens, use a bucket lid remover to crack open the lid on one side to let the excess gas escape, then seal the lid back down. I'm not sure why, as my logical brain tells me it should be otherwise, but over the next several days there will usually be a small vacuum created inside the bucket and the side will pop in a little bit. Don't concern yourself with this. Your bucket will store just fine.
Amaranth Rose, with an advanced degree in Biology and a person who understands these things answered the perplexing question why the buckets preserved with dry ice develop a partial vacuum after a few days. She says, "I've used dry ice and liquid carbon dioxide in electron microscopy work. Liquid carbon dioxide is used to dehydrate samples, as it is miscible in water in all proportions. I suspect the CO2 left in the atmosphere of the bucket is dissolving into the very small percentage of water in the food. It can also slip in between starch molecules and lipids, effectively dissolving into them. This will have the effect of reducing the pressure and volume of CO2 in the exclusion volume of the bucket, until an equilibrium is reached between the pressure of the CO2 in the bucket and the concentration of CO2 in the food stored in the bucket. This would account for the denting of your buckets. Be aware that this is not a chemical reaction and won't affect the food in any way." Mystery solved.