In an effort to avoid hosting a game of bear-bag pin~ata, and also as an excuse to learn something about chemistry, I'm curious about the odor barrier properties of PET soda bottles as an alternative to Opsak or the lighter plastic bags I've seen discussed in this forum. I've been reading about the properties of various plastics and PET seems to have even lower gas permeability than the plastic used in odor-proof bags such as Opsak. I've also been surprised that different plastics seem to have different permeability to different gasses: for example PET is very good at blocking CO2 (important for soda) but is not necessarily as good at blocking O2. I know that odor transmission is all about molecules but don't know which molecules are the important players in food smell and how they stack up against the various types of plastic.
My last two trips were short and I didn't cook. Almost all of my food consisted of peanuts, steel-cut oats, and sport drink mix, all of which could have been stored in soda bottles. My half-baked concept is that if all of the food is in bottles, and if some level of negative pressure could be applied inside the bottle before sealing (such as a squeeze before twisting the cap closed) then there will be very little molecular flow through the plastic and almost all of it will be directed inward. My engineer mind says that this should equate to little or no odor transmission.
Storing cooking utensils in a soda bottle might be problematic, so this concept is primarily aimed at no-cook trips.
Are there any chemists out there who would like to weigh in?
This not an attempt to justify ignoring bear canister or hanging advice: both of those primary food defense measures should benefit from even imperfect odor reduction.
I guess the idea was to eat early and away from camp and wipe the container (and yourself) down (somehow). You'll never get the smell completely off of yourself or your clothing but that's an issue independent of food storage.
Well, PET is probably one of the best plastics to use for just pure odor containment. It is great with the many fragrances out on the market. Fragrances are generally stored in glass, but, depending on the fragrance, is also stored in PET bottles. PET is also good with hydrogen permeability, but I don't know how that translates to odors. The best is aluminum, or metal. A lot of times when you buy an aluminized bag, like a mylar balloon or a squeeze drink container, the material is a 3 layer lamination with aluminum being the middle layer and PET or nylon being the outer layer. Of course, mylar is PET, so there is that. If you took a PET bottle and then sprayed an aluminum layer on it, and then sprayed a PU layer on top to protect the aluminum, you will get the least amount of any gas permeating through.
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I agree with finalyme. Eliminating odors is an exercise in futility. You will be handling food while handling those bottles and so the bottles will smell like food. If there was a way, such as you proposed, to eliminate odors the drug cartels would have optimized it already. Drug dogs still work and bears have a much better sense of smell than drug dogs.
I believe the important compounds you want to suppress are VOC's. Volatile Organic Compounds.
I had an interesting experience with a sniffer dog coming back from an international trip. Waiting for my luggage we watched a lady with a beagle wander around for quite a while checking out bags. After quite a while the dog got to my carry-on bag and took an interest. The Agriculture Agent looked inside and found the peel from the banana I'd finished over eight hours ago in the departure lounge just before boarding. I had gotten rushed and wrapped it in a napkin when I didn't see a trash can handy and had forgotten all about it. That peel wouldn't have lasted an hour in my office trash can but its smell was completely overwhelmed by the complex bouquet from a planeload of tourists in coach.
The sniffer dogs are impressive but they generally are allowed to get pretty close. I didn't get the sense that the dog who busted me smelled that banana before it got right up on it. Maybe it did and was just very disciplined but since people were heading out as soon as their bags arrived I'd think that if it had sensed something from a distance the procedure would have involved a more direct interception.
They say that a bear's smell is much better than a dog's and the background environment in the wild is probably much less complicated than what a compliance animal deals with but there's still got to be a finite detection range that is dependent on barrier effectiveness.
Since their noses probably evolved to detect animals rather than sealed ramen noodle packages I suspect that any bear from a wide area can detect a sleeping hiker from a long way away. That suggests that an active campsite will probably get Cheech-and-Chong-at-the-border level scrutiny and no amount of wrapping should probably considered reliable. I wonder, though, just how far a soda bottle full of peanuts and oatmeal would have to be from a bear's path to be detected without the hiker's presence as a clue. Tens of feet? Hundreds? Are they also cuing on something else, such as an unnaturally-shaped canister or a bag dangling in the breeze to arouse curiosity and intense sniffing? It's too bad there's not a reliable measurement system but if there were I guess the border folks would use that instead of dogs.
I'm planning for a few Grand Canyon trips where the main problems are squirrels, mice, and ravens. The recommended system is Opsak bags inside wire mesh bags. I'm not sure how important the odor part of the equation is: the ground critters probably just explore everything in the area but there must be a reason that odor protection is recommended. I'll be camping at-large off-corridor. Since I'm not planning on cooking I'm thinking seriously about using soda or even water bottles instead of Opsak bags inside a wire mesh bag.
I did an experiment in the back yard, where we have a lot of squirrels and other small and medium animals active. I placed five small piles of shelled peanuts in a wooded, fenced section of the yard next to a creek that the dog can't get to. One pile was just poured on the ground. One was in a thin produce bag tied with a loose NOLS-cookery-style slip knot. One was in a normal Ziplock sandwich bag. One was in a flimsy disposable water bottle. The last was in a PET bottle that once held club soda. I placed a log partly over the bags and bottles just to keep them from blowing away, but not so much that a small animal couldn't bat them around. I also took a picture so that any disturbance would be evident.
Not surprisingly, the first two piles were gone the next morning. The Ziplock fell on the second night. After one week, the two plastic bottles are holding up, and are showing no sign of interest by any of the local creatures. Maybe I should try something stinkier.
Can anyone think of any reason, other than compressibility, why bottles wouldn't work as well or better than Opsaks for granular or powdered foods? Has anyone here done a controlled test of Opsaks?
Loc: Gateway to Columbia Gorge
BPL published a study some years back testing OP sacks using drug-sniffing dogs. The dogs found the OP sacks with drugs every time. Their conclusion was that OP sacks are useless. This contradicts the findings of a test I'd done the year before, using dog food and a dog not trained for scenting.
My own experiment with OP sacks and my dog, using dog food (big motivator for him!) came out as follows: dog food in single freezer bag--even I could smell it. Dog food in doubled freezer bags, I couldn't smell, but the dog went right to it. Dog food in freezer bag inside OP sack, dog ignored. My conclusion was that an OP sack would at least keep the dog from getting into his food when my back was turned. However, bears and most other wild animals have a far more sensitive sense of smell than do dogs!
Also, once you've taken food in and out of the OP sack a time or two, your hands will have transferred scent to the outside of the bag, no matter how careful you are. This will happen with your plastic container, too.
In any case, you need to follow whatever food storage rules are in effect in the jurisdiction in which you're hiking, in this case Grand Canyon NP. Rangers tend to write tickets for those not following the rules.
In the meantime, it sounds as though you have some very happy squirrels!
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey
If you're going to the grand canyon just take your bag of used toilet paper (pack it out, don't bury it) and your container of food (whether bag or hard plastic) and put them both in one larger bag. That should keep the critters away. The secret is to seal both very tightly!