Xanthan gum
A bacterial fermentation gum used in very small quantities to thicken and hold gas — and the ingredient most often wrongly described as replacing gluten.
Also called xanthan (INTERNATIONAL); E415 (TRADE)
Xanthan gum is a polysaccharide produced by bacterial fermentation, used at fractions of a percent of the flour weight. Its molecule is rigid and rod-like, which makes its solutions strongly shear-thinning: stiff when left alone, thin while being worked, stiff again the moment you stop. In a gluten-free batter that behaviour is useful, because the mixture stays workable under the beater and sets up immediately afterwards to hold gas.
What it does is raise viscosity and thereby help retain gas. What it does not do is replace gluten, and the difference matters. It contributes no protein, no extensibility in the way a gluten network is extensible, nothing to browning and nothing to flavour. A loaf built on xanthan alone is a loaf missing everything gluten did except one function.
More is emphatically not better. Increasing xanthan has been measured to REDUCE the specific volume of gluten-free bread, because the batter becomes elastic enough to resist expanding. In one controlled formulation, removing xanthan entirely produced a softer, less gummy crumb with finer cells than the version containing it.
Composition and specification
What too much does
Increasing xanthan gum decreases the specific volume of gluten-free bread, through increased dough elasticity and reduced extensibility. In one measured formulation, removing it lowered crumb hardness from 58.9 N to 46.3 N and gumminess from 35.3 N to 27.8 N, and raised cell count from 11 to 12 cells per square centimetre.
Figures come from one formulation under controlled conditions. BakeHQ relies on the direction — that more is not better — and not on the numbers, and recommends no quantity.
RecordedM. Parsamajd, M. Fazaeli, M. Majdinasab and M.-T. Golmakani, Food Science & Nutrition, R. Torres-Pérez, E. Martínez-García, M. M. Siguero-Tudela, P. García-Segovia, J. Martínez-Monzó and M. Igual, Foods
What changes if it is left out
In a gluten-free bread, gas retention drops and the loaf goes dense — it will still rise and will lose that rise. In a gluten-free cake or cookie, often very little happens, because the batter viscosity and the egg were already doing the work.
Follows from the gas-retention model. The product-dependence is the point: 'do I need xanthan’ has different answers in bread and in cake.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Why the advice about it is usually wrong
Two claims circulate almost universally and neither survives the measured work. The first is that xanthan replaces gluten; it addresses one of gluten’s four jobs and leaves the other three unaddressed. The second is that if a gluten-free bake is dense, it needs more xanthan; the measured effect of adding more is to reduce volume, because an over-elastic batter resists expansion.
The honest position is narrower and more useful: xanthan supplies viscosity, viscosity buys gas retention, and there is a window beyond which additional viscosity costs more than it buys.
Related
What it does
Gas retention
Raises viscosity so gas cells survive proving and the early bake. This is the one job it does, and calling it a gluten replacement overstates it by three.
Binding
Viscosity holds particles to one another as well as holding gas. The two functions are distinct — a binder need not retain gas and a gas-retainer need not bind — but a hydrocolloid at useful levels does both.
The science behind it
Its rigid rod-like molecule is what produces the shear-thinning behaviour that makes it useful and the elasticity that makes too much of it harmful.
Can stand in for
Wheat flour— for gas retention only, and for none of gluten’s other three jobs
The substitution everyone means when they say xanthan replaces gluten, stated at its true scope. It supplies viscosity and therefore gas retention. It contributes no extensibility of the kind a gluten network has, no protein structure, nothing to browning and nothing to flavour. More of it reduces loaf volume rather than increasing it.
Compared in
One side of the comparison readers most often assume is a straight swap.
A rank-one comparison in the observed demand.
Competes for water
Hydration
A hydrocolloid holds water in a viscous phase. That is the point of using it, and it is also why gluten-free formulations take more total liquid than wheat ones: some of the water is committed to the gum rather than free to wet the starch.