What is Xanthan gum ?
Xanthan gum is a polysaccharide used as a food additive and rheology modifier (Davidson ch. 24). It is produced by a process involving fermentation of glucose or sucrose by the Xanthomonas campestris bacterium.

One of the most remarkable properties of xanthan gum is its capability of producing a large increase in the viscosity of a liquid by adding a very small quantity of gum, on the order of one percent. In most foods, it is used at 0.5% and can be used in lower concentrations. The viscosity of xanthan gum solutions decreases with higher shear rates; This is called pseudoplasticity. This means that a product subjected to shear, whether from mixing, shaking or even chewing, will thin out, but once the shear forces are removed, the food will thicken back up. A practical use would be in salad dressing: The xanthan gum makes it thick enough at rest in the bottle to keep the mixture fairly homogeneous, but the shear forces generated by shaking and pouring thins it so it can be easily poured. When it exits the bottle, the shear forces are removed and it thickens back up so it clings to the salad. Unlike other gums, it is very stable under a wide range of temperatures and pH.

In foods, xanthan gum is most often found in salad dressings and sauces. It helps to stabilize the colloidal oil and solid components against creaming by acting as an emulsifier. Also used in frozen foods and beverages, xanthan gum creates the pleasant texture in many ice creams. Toothpaste often contains xanthan gum, where it serves as a binder to keep the product uniform. Xanthan gum is also used in gluten-free baking. Since the gluten found in wheat must be omitted, xanthan gum is used to give the dough or batter a "stickiness" that would otherwise be achieved with the gluten. Xanthan gum also helps thicken commercial egg substitutes made from egg whites to replace the fat and emulsifiers found in yolks. It is also a preferred method of thickening liquids for those with swallowing disorders, since it does not change the color or flavor of foods or beverages.

In the oil industry, xanthan gum is used in large quantities, usually to thicken drilling fluids. These fluids serve to carry the solids cut by the drilling bit back to the surface. Xanthan gum provides great "low end" rheology. When the circulation stops, the solids still remain suspended in the drilling fluid. The widespread use of horizontal drilling and the demand for good control of drilled solids has led to the expanded use of xanthan gum. Xanthan gum has also been added to concrete poured underwater, in order to increase its viscosity and prevent washout.

In cosmetics xanthan gum is used to prepare water gels usually in conjunction with bentonite clays. Is also used in oil-in-water emulsions to help stabilise the oil droplets against coalescence. It has some skin hydrating properties.