I was wondering if you could comment on one aspect of Sky Watcher’s method of filling buckets and removing oxygen. She suggests putting the dry ice in the bottom of the bucket. I have always heard that you should put the mylar bag in the bucket, then fill the mylar bag with grain. Once the bucket is filled, then place a chunk of dry ice on the top of the grain and let it sublimate. Once it is the size of a nickel then you seal the bag and then seal the lid.
Since CO2  is heavier than air, the CO2 will sink to the bottom of the bucket while it is sublimating. I assume it has no problems sinking through the dense grain. I am not certain this is true.
Could you comment or confirm this approach. Sky Watcher’s outline was very informative, but I want to make sure of this one aspect of the process. If you follow the dry ice the size of a nickel, there won’t be any concerns about exploding buckets. Thanks, – Tom T.
JWR Replies: I agree that the best method is to put the dry on top of your grain, where you can keep an eye on it. That is the only way to pack with dry ice safely. If you were to leave too much of it un-sublimated, then you would run the risk of inadvertently creating a CO2 bomb, if you snap the lid on prematurely.
You are also correct that since CO2 is heavier than air, there is no need to put the dry ice in the bottom of the bucket, even if you are packaging flour. The CO2 will make its way to the bottom of the bucket quickly.