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  • Dimitrios Douros

    The Cross-Contamination Myth-Buster!

    Dimitrios Douros

    Reviewed and edited by a celiac disease expert.

      Journal of Gluten Sensitivity Autumn 2014 Issue

    Caption: Photo: CC--Rex Hammock

    Celiac.com 08/22/2016 - The issue of cross-contamination keeps coming up in articles, conferences, blogs and every other venue in which celiacs discuss ways of living with our disease. For all the talk there has been precious little, if any, thoughtful analysis, so I felt it was time for one. Some will appreciate this analysis—others will not. For reference, I don't work for the food industry in any way, shape or form, so I'm not presenting arguments to help anyone make money. I just think that the way gluten permeates our food culture, we celiacs have become overly cautious and worried about where the next molecule of gluten may be hiding, ready to attack us, and as a result walk around in constant fear, significantly degrading our overall quality of our life and doing more harm to our health through stress than a rare, chance episode of cross-contamination might actually do.

    Using the FDA's 20ppm limit as the definition of gluten-free, and some simple, first grade arithmetic, I want to look at the cross-contamination issue and see what's worth worrying about and what's not.

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    Because cross-contamination is a situational, process-related issue, it is best to separate the issue into categories that relate to the situation: a) at home, B) in food production lines shared with gluten products, c) at the prepared food counter in the local grocery store, d) in restaurants.

    What's E.coli Got to do With It?
    Cross-contamination at home is mostly an issue for someone just starting out on a gluten-free life and for those 'blended' families that have some individuals on a gluten-free diet and the rest of the family not.

    There have been many posts over the years with this sentiment: "I just got diagnosed with celiac disease, I have started on the gluten-free diet and other celiacs are telling me to get rid of most of my cooking utensils, especially wooden spoons, plastic spoons, basting syringes as well as brushes I use with oil and butter."

    The concern behind this statement is that porous wood and scratches in plastic spoons and syringes or the hairs of a brush can harbor gluten particles that can contaminate our food. A reasonable sounding argument on the face of it, but one that has absolutely no merit when examined in the light of science and reason!

    E.coli found in beef and salmonella found in chicken are living nasty organisms that multiply and spread and can cause health problems from mild GI upset to death in some cases. And yet there has never been a case of someone throwing away their kitchen utensils after cooking chicken or beef. The utensils—wood, plastic or otherwise—get washed and re-used. If we trust proper washing to get rid of nasty, living, growing organisms that can kill us, there is no reason to doubt that the same proper washing can get rid of some particles of gluten—a non-living, non-growing, non-spreading food ingredient.

    Playing the devil's advocate, let's assume that our washing left behind a thin layer of wheat flour on a wooden spoon—certainly an amount so small that cannot be seen, else it would have been wiped away. How much flour is that? The flour from one fifth of a grain of wheat is enough to completely cover the spoon. One fifth of a grain of wheat is 16mg of wheat; of which no more than 3mg is gluten. So let's assume we use that wooden spoon to prepare pasta in a 1-quart pot and all the flour on the spoon dissolves into the water with the pasta. That's 3mg of gluten in 1,000grams of water (1-quart = 1,000g of water). That works out to around 3ppm gluten in the pot. That is well below the 20ppm definition of gluten-free in the new FDA regulations; it is actually below any level today's best science can even measure! What's more, since we assumed that ALL the flour on the spoon dissolved into the water, the spatula is from now on, forever gluten-free, just as un-contaminated as a brand new spatula from the store!

    Moral of the story: either the washing will remove the gluten from the utensils, or the gluten left over will be below the 20ppm limit in the first food cooked with that utensil and leave the spoon completely uncontaminated ever after. So if you want to use gluten as an excuse to get some new cooking utensils, that's OK, but there is certainly no cross-contamination reason to do so. If you are really concerned, take all your utensils, put them in a pot of boiling water for 10 minutes and you're done! After all, that's how hospitals used to sterilize syringes before throw-away ones became the norm.

    Additionally this argument would indicate that a family that cooks both gluten-free and non-gluten-free could use one set of utensils as long as they get washed after every use. To feel more comfortable, one could use two sets of utensils, one for gluten-free the other for the rest.

    That's False Advertising—I'm Suing You!
    Cross-contamination concerns for foods from shared lines come up as we read food labels that say: "Prepared on a production line that also processes wheat and tree nuts."

    A couple of things to start the discussion: Making customers sick is a bad business plan, the only thing worse is having customers sue for severe illness or death. For these reasons food companies that use allergens in their products - wheat, milk, soy, nuts, shellfish, etc., take the precaution of cleaning their production lines between runs of different products to avoid the very cross-contamination that could sicken or kill their customers. However, in our extremely litigious society, even when a company knows its production line is clean and free of cross-contaminants, it is safer to simply slap the label: "Prepared on a production line that also processes wheat and tree nuts" on the product and completely avoid any nuisance lawsuit.

    Of course this leaves all of us celiacs scratching our heads trying to decide whether it's OK to consume such a product or not. Opinions vary; for my part, I note the label, keep it in mind, but operate on the basis that the company does have a standard process for cleaning their equipment between product runs.

    With that assumption, the only chance of cross-contamination is in the first few batches of the product to go through the line, batches that most, if not all, manufacturers test and discard if found to be cross-contaminated. Even if such a 'spot' contaminated batch made it through to the market the analysis would follow along the same lines as all other cases in this article. The amount of wheat flour (and therefore gluten) that is left on the processing line must be too small to even be seen, otherwise it would have been wiped away. That small amount spread over several 'units' of the product could only result in a few ppm gluten for each 'unit' of the product. Certainly not a cross-contamination concern.

    There's Gluten in Salmon! Really?
    Cross-contamination at the grocery store; primarily a problem in any of the many grocery stores that prepare foods on premises, like sushi and salads or getting fresh-sliced cold-cuts at a deli.

    Pick up a tray of salmon or tuna sushi - nigiri, sashimi, maki—and the ingredient list includes wheat, but the person that prepared it says they don't use wheat. Pick up a salad that obviously has no wheat in it and yet the label lists wheat as a potential allergen. What is going on?

    The most probable culprit in all such cases is the packet of condiments 'on the side'. Sushi almost always includes a sealed soy sauce packet or two for people to use if they want. As we celiacs know most soy sauce contains wheat so, the label on the entire sushi container—which includes the soy sauce packets—lists wheat because of the soy sauce. Skip the soy sauce and enjoy your gluten-free sushi! Same argument with a salad—if wheat is listed as an ingredient but there is no obvious wheat in the salad (croutons, bread, etc.) then the wheat listed is most probably in the dressing offered on the side—skip the dressing.

    Getting fresh cold-cuts at a deli to make sandwiches with your favorite gluten-free bread can raise the question of cross-contamination at the slicer from cured meat products that may contain gluten. First, any reputable deli wipes down their slicer between orders. To add a level of safety, explain the cross-contamination concern and ask the person preparing the order to set aside the first 5 slices—they will always oblige. Any residual gluten will stick to the first few slices and the rest will be fine.

    A Gluten Fog: Your Local Pizzeria—Not That Scary!
    We're all getting used to pizza places that have become enlightened enough to add gluten-free pizza options to their menu. They prepare gluten-free dough and cook the pizza in a dedicated corner of their oven or on baking sheets reserved for gluten-free pizzas. Giving them the benefit of the doubt that they spread out the toppings with no cross-contamination—which is easily checked by a few questions—this leaves one more cross-contamination concern. In 'high end' pizza places that roll their own dough for the regular (wheat) pizzas there's flour dust in the air. It would seem to be a valid cross-contamination concern, but the numbers are again, against it—unless the flour dust in the kitchen is so thick you can't see from one end of the kitchen to the other—not likely because flour dust that thick is a fire hazard!

    So the analysis again reveals a non-issue: the amount of flour dust that lands on a 10" pizza is less than one wheat grain's worth. That's 65mg of wheat, worst case that is 10mg of gluten which translates to less than 10ppm for the entire 10" pizza, again well below the 20ppm definition of gluten-free in the new FDA regulations! So if you're feeling GI distress after eating your favorite gluten-free pizza at your favorite pizzeria, it's probably the pepperoni!

    Salads at a restaurant are the next big concern because of the increasing tendency to see croutons or pita wedges as part of the salad. Of course you ask for your salad without the gluten item. And wouldn't you know it when the salad comes you see a big pita wedge right on top! Of course you ask that they take it back and bring you one without pita. And you wonder—did they make a new one or just serve you the old one after taking the pita off? Or maybe it's a business lunch with an important client and you don't want to make a fuss and don't even ask for a new salad. This is where my analysis goes a bit too far for some. I will remove the pita or pick around the croutons and eat the salad without a worry about getting 'glutened'. In my scientific brain the case is quite simple and clear: the thing we miss the most about gluten is its sticky property—it's a glue that sticks things together, and makes it possible to have light, airy, crusty baguettes to die for! Well, that same great property is what gives me the confidence to eat that salad. During baking, the gluten is completely bound up in that pita or in the croutons—it is not going to come loose just to contaminate me. It has not been laying in wait for the opportunity to be put on a celiac's plate and launch an attack on my villi—it's just not going to happen, nature does not work that way.

    So, worry a little less and enjoy a lot more! I leave you with this empirical fact: There was a report back in the late '90s about a 10-year research program that went around the world interviewing people that were in their 90's to try and find a common thread to their longevity. Every factor was considered, food, smoking, physical activity level, genetics, drinking—everything. Once all the data was analyzed there was one and only one, crystal clear, common factor among all these people: they knew how to let go of worry, stress, loss, pain. Regardless of what life threw at them, they moved past it to the other side and kept on going. Don't let unfounded, irrational fear of gluten rob you of your life—move past it!

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    Speaking as someone that consistently got sick until I burned out and re-seasoned the cast iron skillet I had used for chicken fried steak and gravy, as someone that was sick for days from a half crouton I found at the bottom of my salad (gee, thanks, Chili's) I call bunk on the Mythbuster.


    I think it´s irresponsible and unhelpful to encourage people to be less diligent in watching out for gluten or to give the people trying to live a gluten free life one more thing to have to defend. And, I´m amazed that Celiac.com provides space for this dreck.

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    I understand your point - that worrying about hidden gluten is harmful to health - and I was with you until you got to the pizza and salad section. I am always very clear in restaurants about my need to avoid wheat. Sometimes I have to explain to the server that things like flour tortillas contain wheat! (It's always a surprise to learn just how little others know about what is in food.) Sometimes servers believe that just removing croutons makes the salad gluten free. Not so! I have been very ill after eating a salad with a few crouton crumbs in it. It's nearly impossible to remove the croutons and get all the crumbs, too. I've likewise been ill from eating gluten free pizza that has been prepared too close to the glutenous crusts.

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    It is 100% IRRESPONSIBLE, DANGEROUS, and DAMAGING to the Celiac community to tell them that cross contamination isn't a big deal, that it's okay to pick croutons off a salad, that all manufacturers have high quality cleaning practices and test their products.


    We all have different sensitivity levels when it comes to outward symptoms. However, I know many many Celiacs who react to less than 20ppm. Shared utensils, flour in the air, croutons in salads – all of these things have made many of us sick. This guy doesn't seem to be that sensitive. He is not a myth buster. He is writing about his sensitivity in the gluten free world. He does not represent us as a whole and should not be publishing an article like this claiming that he does.


    Some Celiacs out there will read this article and trust it because they want it to be true. They want life to be easier. And then they will go to a restaurant and tell their friends and the waiter that cross contamination isn't a big deal. And that hurts all of us. That creates more people who will tell me that I'm crazy or overreacting, when in reality I'm right and desperately trying not to get sick. This article and its assumptions are insulting to the Celiac community.


    My full response:


    I agree with Jessica, Heather and Jeff! This is frightening and leads to more misinformation because every person has their own response to gluten. EVERY time we have trusted a pizza place, and most other restaurants that offer "gluten-free" meals, it has not turned out well. It's usually a week's worth of absolute misery that interferes with life for MUCH TOO LONG. This is a dangerous article for those who are extremely gluten sensitive. And we have been navigating this path for many years. It must be nice to "relax" and not have to worry about cross-contamination.

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    I agree with all the ones that have said that this article by this author is irresponsible in his suggestions, etc. I too am extremely sensitive to cross-contamination. I will not pick off the croutons or the bread that was put on top of my food on my plate accidentally. I have been hospitalized and have had several operations for removal of parts of intestine and 1/2 colon and other surgeries and complications until I was diagnosed. Since being diagnosed I have not been in the hospital since and that has been over 6 years now! I have had times where I know I have had cross-contamination as I have been extremely sick for a few days. Celiac is a disease and not something to take lightly as this author suggests. And give me a break - since when do we believe the recommendations by the food and drug administration when it comes to what is "acceptable" in our foods? They are now saying that companies do not need to label that a food is GMO. I recommend that you still have a good time eating out and be as careful as possible. If they deliver that salad with croutons just apologize and tell them it is not a food fad diet but a requirement. They always understand. At least they have with me. And ask for the dressing on the side - most people do that now anyway and then you can just pull out your own and put it on. Or enjoy the natural taste of the vegetables for a change. Ask for lemon to squeeze on the salad. It really is good once you get used to it. Jeff - I agree with you but curious as to why you gave this article a 5 star rating? Bottom line as others have suggested: you know your body so go with that.

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    Science matters. Hysteria, self diagnosis, pseudoscience and confirmation biases simply make things worse.


    Too many people suffer from OCD-like worries when it comes to cross contamination. My daughter had IgA above 100 and a biopsy that showed flat villi 4 years ago. We relied on science on how to safely avoid gluten for her and she is thriving now with no signs of gluten contamination. We eat out regularly and follow common sense. We tell the server that she has celiac disease and make sure that the cook knows. We request that all utensils and the cooking surface are cleaned. We request aluminum foil to be placed on grilling surfaces (she prefers to have no char on her steaks anyway) and never order fried food unless a dedicated gluten free fryer is used.


    There is no denying that people slamming this article have had horrendously bad symptoms. However, just like food poisoning, it is impossible to prove the root cause without having a sample of the food to test. Connecting the dots is a form of confirmation bias ("I have celiac, I ate at a gluten-free place, I have symptoms therefore they cross contaminated my food"). There are dozens of causes that create symptoms similar to celiac. One of them is extreme stress.


    Trust science. Scientists are on your side. Science and the scientific method brings solutions, not problems. The scientific community of professionals cross check and challenge studies and reports. It's the media that twists information to get eyeballs and clicks to get more ad revenue.

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    The PPM math is off. 1 MG = 1 thousandth , 1 PPM = 1 Millionth.


    So your 3 MG of gluten per 1,000 grams of water is actually 3000 PPM!

    1,000g of water =1,000,000 mg. Therefore 3mg of gluten per litre of water is actually 3ppm as claimed in the article

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    For all the shrieking in the comments, this is sensible advice for garden variety celiacs. If you are hyper sensitive, you already know it and can just ignore the advice. Presumably if you have actually been diagnosed as having celiac disease, you are being seen by a doctor fairly regularly. If something prepared in a facility that also processes wheat or a salad bereft of it's pita makes you sick, don't eat it. But don't go trying to scare the bejeezus out of people who aren't that sensitive.

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    I actually am a microbiologist, and this is just the sort of "science" article written by a non-scientist that drives me mad - because it is NOT scientific, and the author is completely wrong in several of their assumptions.


    For example - correlating a living organism (E.coli) with a molecule that triggers an immune response is utterly ridiculous. The E.coli, unlike gluten, on your cooking gear can be killed or removed. Washing, being left in a dry environment for a long period of time or cooking can easily kill E.coli. Also, the infectious dose needed to contract an E.coli infection is very large (it takes at least 100,000 organisms to cause a GI infection, often more) where as autoimmune responses are *very* sensitive, and there are many people with celiac disease who react to LESS than 20 ppm gluten.


    If you want an accurate, science-based analysis of something, stick with science journals that are well documented and referenced so you can actually trace back their claims to the actual data, rather than a list of unfounded assumptions.

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    Each person with celiac disease or gluten sensitivity should make their own decisions about how to handle their diet based on their own situation. This author's approach may not work for everyone, and it is not Celiac.com's position that it will. The whole point of this article is not to let "unfounded, irrational fear of gluten rob you of your life," and this is something that each person affected by this disease ought to try to do, albeit in their own way--one that fits their own situation. There has never been a "one size fits all" diet for those with celiac disease.

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    In retirement from a fortune 500 company, I suddenly found myself diagnosed with celiac disease. I believe in giving back to deserving causes. Celiac disease is now close to my heart.

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