Xanthan gum

One US cup of xanthan gum weighs between 76.8 and 144 grams (2.7 to 5.1 ounces), depending on how the cup is filled and which source measured it. That range is the answer; a single number would not be. Every figure behind it is below, with the method each source used.

Xanthan gum density varies enormously across brands, from about 77 g/cup on NOW Foods' label up to 144 g/cup on Bob's Red Mill and Anthony's labels, an 87 percent spread. NOW's label carries an unusually direct disclaimer — 'this product is sold by weight not volume' — reflecting the fact that this very fine polysaccharide powder measures inconsistently by volume regardless of brand or care taken.

Xanthan gum is a polysaccharide produced by fermenting sugar with the bacterium Xanthomonas campestris, then drying and milling the resulting gel to a fine powder. It was approved as a food additive in 1968 and carries the E number E415 in Europe. In the kitchen, it works as a thickener, emulsifier, and gluten mimic in gluten-free baking. A tiny amount goes a long way — a 1 percent concentration by weight in liquid produces a substantial viscosity increase, and typical gluten-free baking usage is roughly 1/4 teaspoon of xanthan per cup of gluten-free flour.

King Arthur has no xanthan gum entry in their Ingredient Weight Chart at all, so this catalog entry is based entirely on producer nutrition labels and one physical chemistry reference cited in molecular gastronomy sources.

The density spread across the four sources sampled forms three tiers. Bob's Red Mill and Anthony's converge exactly at 9 grams per tablespoon (144 g/cup), and since BRM dominates retail this pair likely represents what most home bakers actually encounter on the shelf. The molecular gastronomy reference sits at 2.5 grams per teaspoon (120 g/cup), plausibly reflecting a lightly-scooped rather than lightly-packed measurement. NOW Foods' current label lists just 0.8 grams per half teaspoon (77 g/cup), less than half the BRM/Anthony's figure. Nutricost, another major supplement brand, carries a similar volume-disclaimer note on their pouches.

The physical reason for the density variance is that xanthan gum is a very fine, low-bulk-density powder with an unusually strong tendency to trap and lose air depending on how it is handled. Particle size grading varies between manufacturers, and finer grades pack differently than coarser ones. Xanthan is also hygroscopic, so a bag stored in humid conditions weighs more per volume than the same bag stored dry.

On top of the between-brand variance, xanthan gum has severe within-sample measurement variance. A heaping teaspoon can weigh two to three times a leveled teaspoon of the same product from the same bag. Because the powder is so fine and clumpy, most home cooks measure it inconsistently even when trying to be careful.

Practical guidance: for typical gluten-free baking use, where the entire recipe calls for 1/4 to 1 teaspoon of xanthan, the density variance rarely matters at the outcome level — even a 100 percent measurement error on 1/4 teaspoon is only about half a gram in one direction or the other. Serious professional or scaled formulations should specify xanthan gum by weight in grams and use a scale accurate to 0.1 gram. The middle of the range around 120-144 g/cup is a defensible fallback for volume-only recipes, but bakers should not expect precise reproducibility between brands.

Common substitutes: guar gum works 1:1 by weight with xanthan in most baking applications and has similar density behavior. Psyllium husk powder can substitute at roughly 2:1 (twice the psyllium by weight) and is often preferred for gluten-free bread specifically.