How Safe Is Your Food? Investigating the effectiveness of odor-proof bags

[Ryan Jordan]

Companion forum thread to:

How Safe Is Your Food? Investigating the effectiveness of odor-proof bags

[HkNewman]

Interesting, though the cover photo is reminiscent of American high school locker sweeps since the late 1970's (kind of had a surprise opening up BPL this AM). By the time I slather blueberry preserves and peanut on a bagel for Lunch #1, I figure these smells coat the outer part of any baggie regardless. Still a very good study but wonder what the lifespan of a ziploc vs. odor-proof bag is if washed after every trip. Got my odor-proofs with my Ursack, occasionally wash and reuse it, whereas with ziplocs they are tossed (unless green-minded girlfriend insists on washing and reusing them.. yeah, she wasn't even a hippy chick either). Think most toss Ziplocs, so further study is likely pointless.

[Herbert Sitz]

I tend to agree with Rob E. I no longer have premium membership to read the BPL article, but it seems to me there is a big difference between testing at close range and at more of a distance.

I know I can reliably and quickly distinguish between a faint odor and absence of odor at very close range. As distance increases that ability disappears. I see no reason why this would be different with dogs or bears. And I'm pretty sure that as distance is added the ability to discern odor from an OPSAK would fail more quickly than ability to discern odor from a ziploc.

I csn personally confirm that there is a big difference between the amount of odor that escapes a regular ziploc and what escapes an OPSAK. I can't smell odor from OPSAK even at close range, although of course I'm not surprised that a dog or bear could. But increase distance of dog or bear from ziploc and OPSAK to 10 yards, 100 yards, a quarter mile, or longer, and I suspect at some distance the animal will be able to smell contents of the ziploc but not be able to smell contents of OPSAK. Of course that's much harder to reliably and easily test.

I say all of this with belief that bears have powers of smell greater than any dog. I believe there are studies that show that, although for now I'm satisfied with this from Wikipedia: ". . . the Silvertip Grizzly found in parts of North America, ha a sense of smell seven times stronger than that of the bloodhound. . .". Wikipedia entry on Olfaction

[Will Tatman]

Well done article, I appreciate the thoroughness.

As someone who uses OpSaks exclusively for food protection, I will now have to do some further thinking about food selection and packaging. As a vegan, I don't interact much with Cheese or Salami, which I assume might hold the titles for 'stinkiest trail foods' But I do hike with Peanut Butter, a top contender. I tend to just throw a jar straight into an Opsak along with my day-to-day meals (themselves in a gallon bag per day), and one extra ziplock full of trash. At the end of the day, I seal up the opsak, wrap it in a wind jacket, and use it as a pillow. Same method I used on the GET last year with no issues. So, not terribly comforting to read this article, but until I know more about how proximity, layering, and food selection factor in, not enough to deter me from continuing to use OpSaks instead of hanging or canisters (at least in the desert/mountain SW).

[John Nausieda]

There are ways to beef up the sealing of an Opsak by using this product at Amazon.
http://www.amazon.com/gp/product/B0007D6KEU/ref=oh_details_o08_s01_i00?ie=UTF8&psc=1

Also wondering if Nylofume bags were mentioned or could be studied in the future.

[Stephen Barber]

@ Rob and Herbert:

Since you didn't read the article, let me summarize it: There was no real or statistical difference in the dog's ability to locate drugs enclosed in either a ziplock or OP bag.

If there is no difference at close range, enclosed in a locker, indicating that about the same quantity of scented molecules are escaping each type of bag, I don't see how you can expect a difference at a distance when the food is enclosed within a bear bag or pack?

[Billy Ray]

If an 'odor-proof' bag just slows down the emissions of smells, then it may do you some good. Reduced emissions my reduce the distance at which bears can pick up a trace of things inside. In other words, a bear may need to be, say, closer than 100 yards to pick up the smell of something in any plastic bag. Whereas a bear a half a mile away may pick up the scent of food outside of a bag. So it could make a difference as to whether a bear comes to your camp or not.

In addition, it seems to me the above study did not determine if the Op Sack could reduce odor emissions to a lower level than that of a regular zip lock. It may be that it does, but both were over the threshold of what was required for the dogs to pick up the scent in such a small area as was used.

That's my 2 cents.

Using the above logic it may be a good idea to line your bear canister with a plastic bag.

Bill

[Andrew Zajac]

I think this study was great and shows that the most important aspect of avoiding negative interactions with wildlife is your behavior. I also really appreciated the inclusion of some statistics. Speaking from the perspective of finishing a masters thesis in ecology, statistics can get nit picky to a ridiculous level. This is usually (from my perspective) to no appreciable gain in understanding or interpretation of the data, so I won't nitpick methods. However, there are accepted ways of reporting these statistics that allow the reader to know what tests were performed and what the results are. These can be found with a quick google search and their inclusion would be much appreciated.

[David Wood]

I've carried a small ziplock bag of curry spices for livening up meals in the past – trouble is everything in the pack smells of curry by the end of a weekend (it should be obvious I'm not talking about bear country here).

However, placing the spices in an small OP sack completely removed the problem.

Interestingly though – I could just smell the spices through the OP sack if I sniffed at it up close.

I've also used them when carrying out empty cans of fish we'd eaten on really long hikes (multi-week) where we could resupply at huts regularly but only dump rubbish occasionally and hadn't good access to detergent based cleaning. The smell of three day old cans of fish cannot be disguised easily in a pack. The OP sacks solved that.

Just pointing out that (as Ari mentioned above) it's not that they have no effect at all, just that it's not 100% as they claim. There are uses for them, and maybe they even reduce the chances of a bear catching the scent – but that's likely to remain conjecture.

[Heather Branch]

I debated whether to renew my BPL membership. This article alone makes me glad I did! I will continue to use my Backpacker's Cache bear barrel [with liner bags and twist locks], despite its weight. I am glad to see I am not the only one who found the OPSak closures terrible. It would be smart if they improved the closures. What I do is put essential food in my bear barrel, put the barrel well away from my site at night, and start out with overflow I could survive without [e.g. coffee and my extra night freeze dried food package] in an OPSack hung in a very light cloth bag at bear bag height etc dimensions or as close as possible. Coffee is pretty essential for many of us, I know, but I always put caffeine pills in the barrel as backup:)

[Mary D]

I did a similar experiment a few years ago, using dry dog food with zippered freezer bags (Ziploc brand) and with OP sacks (Loksak brand), and my Labrador/Golden Retriever cross dog (service dog reject). I was concerned because after I packed my dog's kibble into single-serving freezer bags, I could smell the food through the bag, and my nose isn't very sensitive. My results contradict this study.

I tried two layers of freezer bag. That worked for me, but when I left it on the floor, my dog immediately pounced on it and tried to chew into the bags.

I then put a single freezer bag with dog food inside an OP Sack and left it on the floor. My dog walked right by it several times without noticing the smell.

I ran this trial several times, with pretty much the same results. The only difference was that my dog became conditioned to associate a plastic bag on the floor with food, so after a couple of replications he started sniffing the OP sack before moving on. He still did not detect the food inside.

Admittedly, my dog, although of a hunting breed, has never been specifically trained to follow scents, but his food, for him, was an extremely powerful motivator. To motivate him more, I ran the tests just before dinnertime (which caused a lot of barking). Since he didn't smell his food inside the OP Sacks, I had to assume that the OP sacks are at least somewhat effective. The single freezer bag plus OP sack was definitely far more effective than doubled freezer bags.

It may be that those "controlled substances" have a more powerful smell than dry dog food. Or it may be that my dog has a lousy sense of smell. But at least with the OP sacks, I didn't have to worry about my dog getting into his or my food!

Since bears reportedly have a much stronger sense of smell than do dogs, both this study and my one dog study may be moot. However, I have read several anecdotal reports from reliable persons of a bear walking right by a hanging OP sack without investigating it (in most cases the OP sack was inside an Ursack). Maybe the bear wasn't hungry? Or had a head cold?

I will continue to use odor-proof sacks, although I would never rely on them alone, only as a supplement to my Ursack or canister. Nor would I use them to store food inside my tent. But I have demonstrated to my own satisfaction that OP sacks keep my dog out of the food!

PS: I fully agree with others above about the OP sack seals; they're horrible! I plan to try the Nylafume bags, although my dog won't be with me this summer.

I'd love to see the results of a similar trial using mice or other rodents. I had one get in my car one time while I was on a 3-day backpack trip; it ate most of an apple I left on the front seat. It also evidently investigated an OP sack in the back of the car that contained food for a subsequent trip. There were mouse droppings nearby, but no evidence the sack had been chewed. I never figured out how the mouse got in my car, but another backpacker reported the same thing happening at the same trailhead a week before.

[Herbert Sitz]

Stephen — The test is what I assumed it was. That test does not indicate that the "same quantity of scented molecules are escaping each type of bag". It indicates, or is at least consistent with, there being enough molecules escaping each type of bag for both to be easily detectable by the animal, even for them to seem roughly equally strong at small distances. As distance increases, however, if one bag is allowing fewer molecules to escape then it could become undetectable sooner than the other.

I'm not saying I know this is the correct explanation for the test's results. I'm saying that the above explanation is consistent with (1) common sense, (2) my own experience that OPSAKs let out less odor than ziplocs, and (3) the BPL test.

To claim that there is no difference between OPSAKS and ziplocs is inconsistent with my own experience (there's a clear difference for me and other people), so it's hard for me to believe that there is "no difference" between them for dogs and bears. I'm not saying the test was wrong; I'm just suggesting that the conclusions people are drawing from it are stronger than the results of the test warrant. That is, there is another explanation for why there seems to be no statistical difference b/w OPSAKs and ziplocs for dogs at close range, and that explanation squares better with my own experience (and with common sense that as you make a barrier stronger (e.g, double bag vs. single bag ziplocs), fewer items will cross it).

[Rob E]

Stephen, the difference between the ziplocks and the odour proof bag has to do with absolute detection levels and dilution. Close enough the scent density coming from both bags is higher than the absolute detection level of the dog, but further away when you have dilution and spreading, it might become significant enough to drop below the absolute detection level.

I will use a rough analogy, so bear with me (pun intended): If I can hear both a whisper and an airhorn from 1 foot away, should I expect to be able to hear both 500 feet away? Up close sound volumes from both sources are above the absolute detection level of my ears, but further away the drop in energy manifests itself as an inability to hear the whisper.

[Cayenne Redmonk]

Once the dogs knew there was something to find, they worked hard for their reward.

At first the dogs were playful, but once conditioned to realize they were in the room until they found the drugs….

Dogs are highly conditioned to please their worker.

How many false positives were there in a locker room with no drugs given the same conditioned dogs ?

[Bruce Warren]

I expected that result. I bought a pack of those bags 6 years ago. After working at Dow Chemical for a while, I was under the opinion that no thin plastic polymer will block the passage of aromatic hydrocarbons for long. Only metal does. I did a raccoon test on my porch using the aluminum coated anti-static bags sold for storing circuit boards. See them at uline.com, they are much cheaper and come in lots of sizes. They also totally block moisture and do a good job on blocking oxygen. I have stored crackers in an antistatic bag for two years and they were not stale.

I carefully put cat food inside the anti-static bag and made sure nothing touched the outside. I zipped it up good and laid the bag on the porch. Oscar the Raccoon had been eating the cat food from the bowl for a few weeks. With no food in the bowl that night, I checked the next morning. I saw muddy paw prints on the anti-static bag, but he did not chew on it at all. That told me that no bear will smell it either. But one caveat, after using an aluminum coated bag a few times the aluminum coating will get scrapes or maybe tiny holes. I wrinkled a bag all over for a few minutes and dragged it over my gravel driveway a few feet. Repeating the same Oscar test, he ripped open the bag and ate all the food. There were no holes when I did a water test. So put your anti-static bag inside another bigger one when you use it; making two layers, treat it gently and it will last a long time with no odor leaks

[Jay Wilkerson]

Excellent read and very informative! Wonder if freezer bags make a difference?

[Mitchell Rossman]

Very good study!

As a Ph.D. Chemist, I find this problem to be very interesting.

However, if you did develop a truly odor-proof bag, you might get a visit from your local DEA agent.

[Walter Carrington]

Many thanks for doing this careful study.

I have asthma and am very sensitive to some chemicals used for cleaning. I've put my clothes in nylofume, hunter's scent proof bags and black plastic garbage and contractor bags to prevent my clothes from picking up these odors when traveling. The nylofume and hunter's scent proof bags are much better than other plastic bags at keeping out chemical odors — the odor detector was my [human] nose. So odor proof bags reduce the odors passing through. On the other hand, it is impossible for a hiker to be as careful as the experimenters to avoid contaminating the outside of the bag.

But I doubt that this makes much difference for food bags versus bears. I think most of our guesses on how well various tactics work is based on our experience of human abilities. Dogs or bears have abilities that are difficult for humans to really comprehend.

[Bob Gross]

Many years ago, before we had bear canisters in Yosemite, we had to hang our backpacker food at night. Still, the black bears knew where to look, and they climbed the trees to pursue the Mountain House prey. We were looking for a way to mask the food odor, so we started using moth balls. We would place a moth ball in the top of each food bag that was hung in the tree. For a while, it looked like that was going to work. Then some black bear stumbled onto the food anyway, and it got a good whiff of the moth balls. So then it associated food smell with the smell of moth balls, so the moth balls became more of an odor attractant than a mask. The entire experiment was a failure.

–B.G.–

[Kirk Nichols]

Reynolds Oven baking bags are Mylar. I have human nose tested them and no one (human friends) could detect the freshly ground coffee inside though they could smell the grounds through six layers of zip-lock bags. Are the dogs available for another round of testing? The food bags in the image are inside an electric bear fence that runs on one "D" cell.

[Stephen Barber]

Rob and Herbert: You're right, I'm wrong on specific molecules dispersion rates. The test doesn't measure absolute rates.

However, the fact that both bags remain detectable by a critter that has only 1/7th the sensitivity of a bear (according to some reports) strongly suggests to me that the difference in real life is minimal. Smells do seem to penetrate the ziplock more quickly than the OpSak, but both are penetrated and dispersed.

This is the first time I've seen OpSak vs ziplock bags actually tested in a controlled situation. Anecdotes are interesting and suggestive for more(controlled) experiments. This test bears (again the pun!) more weight to me than a ton of anecdotes, to the end that, given the permeability of the OpSak bag, its poor seal and its expense, I will not be buying or using anymore until further testing shows the OpSak or its improved offspring to actually block odors. The OpSak's minimal usefulness in blocking odors is not something I care to rely on.

Neither I nor my dogs have ever noticed any difference between ziplocks and OpSaks re smells.

YMMV.

The anecdote regarding metal covered plastic bags is interesting – there's a good line to follow up with testing and development.

[Ike Jutkowitz]

Lots of great discussion points!

Some general comments: Remember that this study is an experimental model. It is left up to the individual reader to determine how applicable he or she feels the results are to their intended use of the product. Using this model, we were not able to demonstrate any differences between the odor-proof bags and ziplocs. This doesn't mean that there aren't any. As discussed in the article, the dogs work at close range and are trained to signal on even minute amounts of the substances in question.

On the other hand, I have yet to see any strong scientific evidence to suggest that the bags do work any better than ziplocs. Without that proof, and with reasonable evidence to the contrary, why should I blindly believe the theory?

In the end, I believe that our conclusion was appropriate and not overstated. The bags are not 100% odor-proof as advertised. Not only did the dogs find them, but even long after the bags had been removed, dogs would repeatedly signal on the open lockers that had previously held study bags. Scent had been transmitted to the immediate environment.

Specific responses:
@Kyle- thank you for the kind words. I agree that proximity is a limitation of the study. However, the dogs' range is much longer than you think. The handlers like to talk about scent cones. Picture a 3 dimensional structure, heaviest at the source, and radiating outward in a cone-like pattern. The dogs are not actually searching for the object locker by locker as we would do, but instead run laps until they intersect the scent cone. It is very obvious when this happens as their behavior suddenly changes and they practically fall over themselves in their hurry to reverse direction and follow the cone. Study bags contained as little as 5 grams of scent, and as described earlier, this was vacuum sealed in freezer (foodsaver) bags, then wrapped in heavy canvas, then sealed in the study bag. So we are already talking about a trace quantity of scent that is doubly wrapped. Despite this, we saw the dogs hit scent cones from 10-15 feet away. Then they'd run straight to the appropriate locker. How big would the scent cone be when we are talking about 3-5 pounds of food, a stinky odor source approximately 320x larger than what we used and carried by the wind? I'm guessing it would be a pretty large cone.

@Luke and Jay- see my first post in this thread and the details above. Vacuum sealed freezer bags did not prevent odor transmission.

@John- we did not assess the nylafume bags, but may yet do so in an upcoming larger scale study. However, after this pilot study, my enthusiasm for doing so is low. I went into this first study not knowing what we would find (to the officers' credit, they never doubted the dogs for a second). Now that I've seen the dogs at work, I have little hope that a pack liner with a giant hole in the top would have any chance. We are hoping to look at some heat sealable mylar bags, but I will include a couple other odor-proof options if we can do so without making the project too cumbersome for the dogs and handlers.

@Rob, Bill, Stephen, and Herbert- Interesting discussion. We used the timed trials in our model to hopefully pick up on subtle differences between ziplocks and odor-proof bags, and were unable to detect a difference. To definitively answer your question, I think a large scale in situ study is probably needed.

@Redmonk- No false positives. When they knew, they knew, and they would bark and hit the lockers until acknowledged.

@Kirk- heat sealed mylar will be evaluated hopefully next month.

I appreciate all the comments and feedback even if, in the interest of space, I have not responded personally. Thanks again.

[JP]

–

[Richard Colfack]

Excellent article. No longer will I waste good money on OPSAKs. I've always been unimpressed with their durability and despise the crappy closure (not too mention their ridiculously high cost for a Ziploc bag) but I always put up with this thinking it helped keep bears from slaughtering me in the tent.

[Roleigh Martin]

Bruce, thanks for the posting about anti-static bags.

I looked at UsPlastic.com web site for choices. The anti-static bag choices are here:

http://www.usplastic.com/catalog/item.aspx?itemid=24643&catid=883

Postscript: I see there are two types of anti-static bags, those that are poly-based and those that are aluminum based. Uline has the aluminum based ones here:
http://www.uline.com/BL_57/No-Print-Static-Shielding-Bags-Reclosable

I wonder how these anti-static bags compare with biohazard specimen bags.

http://www.usplastic.com/catalog/item.aspx?itemid=75825&catid=883

The Nyloflume bags look interesting but I see (a) that you should always use two of them, per recommendation, and secondly, they do not have a ziplock. A good ordering place is here though:

http://www.quantumtermite.com/termite-products-and-paperwork/nylofume-bags-20
http://www.carnivalfumes.com/nylofume_bags.pdf

In all 3 alternative bag choices. It would be nice to know which of the 4 (the 4th being OP bags) work best. 4 and 5 if you distinguish between the two types of anti-static bags.

[Author]

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