Actually, gluten-free means that there's a very small proportion of gluten in relation to the product, not that 100% of it has been removed.
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"The current international Codex Alimentarius standard allows for 20 parts per million of gluten in so-called "gluten-free" foods" - http://en.wikipedia.org/wiki/Gluten-free_diet
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It's enough to prevent exacerbation of symptoms for those with gluten sensitivity, but it's not a complete removal.