In this article, "Let's Talk Gluten Replacers" from Art of Gluten Free Baking, there is a terrific description of the process used to create xanthan gum that clarifies why xanthan gum does not contain any corn, wheat or soy.
So, let’s talk about xanthan gum. It’s what I use and what I feel works best in the baking I do. And, there is a lot of misinformation floating around about xanthan gum that I want to clear up. Clearly, you need to choose what’s best for you, but I really want folks to make a truly informed choice.
As described earlier, xanthan gum is made from the fermentation of the bacteria Xanthomonas campestris. What this means is that the bacteria is introduced to a sugar solution—which is most often made from wheat, corn, soy, or dairy. The bacteria is broken down during the fermentation process, creating a by-product—xanthan gum. The xanthan gum is then harvested and dried into a powder.
What is important to note about the process is that the xanthan gum is a product of the process that uses Xanthomonas campestris and the sugar medium. It is not, itself, either of these things. It is something new. What this means is that xanthan gum is no longer the sugar it’s grown on. This is one of the reasons why xanthan gum can be grown on something like wheat sugar and still be gluten-free. The other reason is that the growing medium is sugar. And the sugar is not the part of the food that people react to when they have a food allergy/intolerance/sensitivity—including celiac. The part of the food people react to is the protein (in wheat the protein we react to is the gluten). Since there is no protein in sugar, there is no gluten in wheat sugar.
According to the food scientists I’ve spoken to and the research I’ve done, this means is that no matter what sugar medium the xanthan gum is grown on, scientifically there is none of the protein associated with that growing medium in the sugar or the resulting xanthan gum. Therefore, if you avoid xanthan gum because you think it’s a corn product: it’s not. And, if you avoid xanthan gum because you’re allergic to thing that provides the sugar for the growing medium: you may not have to.
Of course, you could be sensitive to the xanthan gum itself (or to guar gum or to the seeds). But I think it’s important to be clear with yourself about what you’re sensitive to. If you avoid xanthan gum simply because of reading incorrect information about it, you might want to give it a chance.
Statement from Bob’s Red Mill about their xanthan gum:
“6/11/12 UPDATE: Regarding corn in xanthan gum: The microorganism that produces [Bob’s Red Mill] xanthan gum is actually fed a glucose solution that is derived from wheat starch. Gluten is found in the protein part of the wheat kernel and no gluten is contained in the solution of glucose. Additionally, after the bacteria eats the glucose, there is no wheat to be found in the outer coating that it produces, which is what makes up xanthan gum. The short answer here is, there is no corn used at all in the making of [Bob’s Red Mill] xanthan gum.”