[Maverick88]

I haven't exercised it yet, but i have heard many times over the years that you can drop a peice of dry ice in to a container to dispell the oxygen in it before storage. Just make sure you don't seal the lid on what ever you are using until the dry ice has disapated because it will presurize the container and eventualy burst.

Pros and Cons to this method?

 

[Rifleman336]

Got a phsysicst or a chemist can tell you for give amount of dry ice how many square meters of gas in becomes when it melts. From what I've been told one puts a chunk of dry ice in and as it off gasses on has the lid of the container almost closed with a match or a candle just at the entrence. As the dry ice melts the oxygen will be purged and thus when the candle or match gets snuffed out buy the gasses coming out the little crack you aloud the gasses to come out you then can close the container with oxygen expelled.

Another trick is to get some "oxygen eaters" used for storage of food, it chemical eats the oxygen in a give container to preserve it's contents.


Yet another trick is to use a candle in the container, one lights the candle and then closes the lid and then the candle burns up the oxygen to very low levels than it should cause rusting of any metal inside the container.


Rifleman 336

 

[trainedtosave]

Got a phsysicst or a chemical can tell you for give amount of dry ice how many square meters of gas in becomes when it melts. From what I've been told one puts a chunk of dry ice in and as it off gasses on has the lid of the container almost closed with a match or a candle just at the entrence. As the dry ice melts the oxygen will be purged and thus when the candle or match gets snuffed out buy the gasses coming out the little crack you aloud the gasses to come out you then can close the container with oxygen expelled.

Another trick is to get some "oxygen eaters" used for storage of food, it chemical eats the oxygen in a give container to preserve it's contents.


Yet another trick is to use a candle in the container, one lights the candle and then closes the lid and then the candle burns up the oxygen to very low levels than it should cause rusting of any metal inside the container.


Rifleman 336

Ok, just so happens I am a chemistry major. The gas dispels oxygen because carbon dioxide is heavier than oxygen (higher molecular weight) I won't go into technicalities because I am not sure how much you know about chemistry. 44 grams of dry ice will become a gas, at very roughly 0.022 m^3, or 220 cubic centimeters. It is a bit of math, but you can find the volume of whatever container you are using, let's take a 5 gallon bucket.
Measure the height of the cylinder, the radius( measure halfway across the bottom at the widest point of the circle). The volume is the height x the radius squared x 3.14( or you can just google it. Fill the container and guestimate how much volume of air is left.

I rambled a bit, but hopefully this info was useful.


Almost forgot, for a solid 28grams=1 oz

 

[Lowdown3]

Basically since oxygen absorbers and mylar liners have become more commonly available- late 90's, most people have moved away from some of the dinosauric methods.

Dry ice flush still will not serve as a LONG TERM oxygen barrier. You can't use it with mylar, so you still have no protection against oxidation long term.

Mylar and oxygen absorbers is SAFER to use, more readily available and produces a better product.

The dinosaurs went extinct for a reason

 

[Levant]

I used to use dry ice to expel oxygen when packing wheat in buckets. The problem is, assuming you do everything else right, any movement of the bucket after the dry ice is dissolved will expel CO2 and allow atmosphere, at approximately 21% oxygen, back in.

An oxygen absorber, on the other hand, works after the container is sealed so no oxygen can get in afterward. by removing the oxygen, you're left with 99% nitrogen - which is exactly (well, 100% nitrogen is more exactly) what the best dry packing systems use to displace the oxygen with.

 

[lowflyer]

Dry ice/CO2 for storage

O2 absorbers are the best way to go but if you don't have/can't get them CO2 can be used.

I have used dry ice once to preserve grain in food grade buckets that I get free from grocery store bakeries.

I was experimenting so I tended to use chunks that were too big and, consequently, kept off-gassing for a lot longer than necessary.

I thought the D.I. had evaporated and stacked up the buckets only to come back about an hour later and find them rolloing around like a bunch of misshapen basketballs -- the seals on these buckets are top notch, BTW, and hold the gas in very well. I use a dead blow 1# hammer to reseat the lids thoroughly.

A new method I just tried is to use a CO2 tank from a kid's paintball gun, attach the tank-to-gun adapter and use its threaded fitting to control the rate of flow and act as a shutoff for the gas. It cost $4.00 at ****s Sporting Goods to fill the tank and it should do a truckload of buckets.

You release the gas slowly, controlling it by how far you screw the adapter on to the tank, and shut it off by unscrewing it till the auto-valve shuts off the flow. It only takes a 5-10 second shot, AT A LOW RATE, to fill a bucket -- CAREFUL or you'll blow grain all over the room!

Test the gas level with a lit match which should go out when lowered below the bucket rim. carefully place the lid on the bucket, hammer it down to seal, and label it to show contents, date, and confirm it had CO2 in it.

Don't wave the lid around and do this in a room with still air to keep from allowing room air to get back into the bucket.

 

[MikeK]

Any form of gas flushing still leaves quite a bit of O2 behind. As much as 5% in some cases. Where an O2 absorber gets it down to what, .2%, or something like that?

Some bugs don't need much O2 to survive and can even survive a generation or two in the .2% from an O2 absorber. Imagine how many generations could survive in 3-5%.

Also, the intense cold of dry ice is a good way to get frozen condensation in with the foods, which will thaw and become moisture later on.

The storage food industry stopped using gas flushing as soon as something better was available. They use O2 absorbers now.

 

[lowflyer]

Mike,

That's good information and since O2 absorbers are so cheap and readily available it makes sense to use them.

I'll probably go back and put them in all my buckets before all's said and done.

 

[bsteve]

Ok, just so happens I am a chemistry major. The gas dispels oxygen because carbon dioxide is heavier than oxygen (higher molecular weight) I won't go into technicalities because I am not sure how much you know about chemistry. 44 grams of dry ice will become a gas, at very roughly 0.022 m^3, or 220 cubic centimeters. It is a bit of math, but you can find the volume of whatever container you are using, let's take a 5 gallon bucket.
Measure the height of the cylinder, the radius( measure halfway across the bottom at the widest point of the circle). The volume is the height x the radius squared x 3.14( or you can just google it. Fill the container and guestimate how much volume of air is left.

I rambled a bit, but hopefully this info was useful.


Almost forgot, for a solid 28grams=1 oz

Dude, you are giving us chemists a bad name. You really want to figure out the volume of a 5 gallon bucket by multiplying its height by radius squared by pi? And you did not answer the question pose.

5 galon bucket is about 19 L, or roughly the 0.022 m3 (the aprx volume of 1 mole of gas at STP), which trainedtosave mentioned. 44 grams (i.e., 1 mole) of CO2, will just about fill up that bucket. Given that you need a bit more in order to flush it, given that CO2 (44 g/mol) flushes air (~29 g/mol) rather well if the dry ice is on the bottom and the escape is at the top, that some space is taken up by the foodstuff, and that you'll need the dry ice to generate about 2 or 3 times the volume of gas to flush all of the air out well, I'd say that:

(1) use 2 to 5 oz, of dry ice per 5 gal bucket (less then 2 wont flush air out, more than 5 will be wasteful); and

(2) you must let the escaping gasses out of the container through a hole as tiny (say 1/16") as possible.

As soon as the gasses stop escaping, just plug up the pinprick hole. Burping the lid will introduce too much air into the container.


PS: Assignment for trainedtosave: just how many cubic cm are there in 0.022 m^3? : Extra credit: How much O2, in percent of total volume, will there be if Maverick drops 5 oz of CO2, into 5 gallon bucket filled with rice? Assume kB = 1.38×10^-23 J/K, 1/16 inch effusion orifice, first order sublimation of CO2 with half life of 1 hour, each rice grain is a sphere with a 2 mm diameter, and cubic closest packing.

 

[Carne Frio]

" Almost forgot, for a solid 28grams=1 oz. "

Yeah, I remember that one from my college days.