I just had to pull the Joe Pastry train off to the side tracks for a moment to extoll the virtues of a truly amazing ingredient: xanthan gum. Oh sure, people demonize it, but usually without bothering to find out what it really is or does. The fact that it sounds “science-y” is enough to elicit derision or even contempt from a certain stripe of organic bandwagoneer. Yes, there is the very rare individual that’s allergic to it. But people are allergic to all kinds of things, are they not?
Xanthan gum was invented in the heyday of corn sugar fermentation research, the 1960′s. At the time, folks in the USDA labs were looking for a thickener that was more versatile and efficient than corn starch and easier to produce than guar gum. One day, they allowed a culture of a bacterium by the name of Xanthomonas campestris to feed on a solution of corn-derived glucose. What resulted was a slimy, colorless substance that turned out to be one of the most broadly useful food ingredients currently known to man. For it turns out that in the process of digesting the glucose, the bacteria rearranged the individual sugars into longer-chain sugars (polysaccharides) with truly amazing properties.
What are those properties? For one, thickening. Applied in proportions of as little as a quarter percent, xanthan gum can increase the viscosity of a fluid that pours like water into one that pours like motor oil, making it highly useful for things like salad dressings. But that’s not all it can do. It can stop the formation of ice crystals in ice creams, replace the fatty mouthfeel in low-fat dairy products, and act as a stand-in for gluten in gluten-free baked goods.
But for me the most amazing property of xanthan gum is its pseudoplasticity, which is to say its ability to take on different consistencies according to how much force is applied to it. This phenomenon — also called shear thinning — is most commonly witnessed in ketchup bottles, whereas the ketchup is thick when it’s sitting still, thins out when its shaken and poured, then thickens again when it comes to rest. Of course liquids like sauces aren’t the only applications for this sort of behavior. Shear forces are also applied in the course of chewing. That makes xanthan gum highly desirable in a thing like a cheesecake, which you want to hold its shape on the plate and on the fork, but which you want to lose thickness rapidly once it’s in the mouth.
As an extra-geeky side note, I should add that shear thinning is frequently confused with thixotropy, which is a similar phenomenon, but which takes place over a lengthier period of time. Shear thinning happens fast, almost instantaneously. Just so we’re clear on that.