Last reviewed: 8 May 2026
The fermentation-grown gum holding UK salad dressings and gluten-free loaves together
E415 is xanthan gum, a high-molecular-weight polysaccharide grown — not extracted from a plant. The bacterium Xanthomonas campestris is fed a sugar feedstock (usually glucose or sucrose, sometimes lactose) in a fermentation tank. The bacterium secretes the polymer as a slimy capsule around itself; the broth is then heat-killed, the polymer precipitated with alcohol, dried, and milled into the off-white powder food manufacturers buy by the sack.
Industrial production was developed by the US Department of Agriculture's Northern Regional Research Laboratory in the late 1950s and 1960s, and xanthan moved into commercial food use through the 1970s. It is one of the few food ingredients whose entire industrial supply is biotechnological rather than agricultural — there is no xanthan plant, no xanthan harvest, only stainless-steel fermenters.
Structurally, the polymer is a cellulose-like glucose backbone with trisaccharide side chains hanging off every other glucose unit. Those side chains carry charged groups (acetate and pyruvate), and that branched, charged geometry is what gives xanthan its unusual rheology — a property called pseudoplastic or shear-thinning behaviour. At rest the polymer chains tangle into a gel-like network; under shear (whisking, pouring, chewing) the network breaks down and the liquid flows freely; the moment the shear stops, the network re-forms. That is why a salad dressing thickened with xanthan clings to a leaf instead of pooling at the bottom of the bowl, but pours cleanly out of the bottle.
Xanthan is a workhorse because a tiny amount goes a long way and the resulting texture survives almost anything the manufacturing line throws at it.
Once you know to look, xanthan gum appears on roughly half the bottles, jars and pouches in a UK supermarket's chilled and ambient sections.
On UK labels it appears as "E415", "xanthan gum", "thickener: xanthan gum" or "stabiliser: xanthan gum" depending on the manufacturer's preference.
In wheat dough, gluten proteins form a stretchy network that traps the carbon dioxide produced by yeast or baking powder. That network is what gives bread its open crumb, cake its springiness and pastry its lift. Strip the wheat out and that network goes with it — gluten-free flours alone produce dense, crumbly, brick-like results.
Xanthan gum is the most common single substitute. At about 1 to 2% of the flour weight (a teaspoon per cup) it produces a polymer network elastic enough to hold gas bubbles through proving and baking, giving gluten-free loaves an actual crumb structure. UK gluten-free recipes and commercial mixes lean on it for exactly this reason.
Most UK gluten-free formulations combine xanthan with guar gum rather than using either alone. Guar binds water and gives bulk; xanthan supplies elasticity and acid stability. Together they imitate gluten's behaviour more convincingly than either does on its own. We covered the guar side in detail on the E412 (guar gum) guide.
This is the section IBS readers come looking for, because the two gums get lumped together and the picture is genuinely different.
Monash University's FODMAP database — the reference clinicians use — classifies xanthan gum as low-FODMAP at typical food serving sizes. It does ferment in the colon (every soluble fibre does to some degree), but the amounts present in a normal portion of dressing, sauce or gluten-free bread are small enough that most people on a low-FODMAP elimination diet tolerate it.
Guar gum (E412) is the opposite picture: Monash classifies guar as high-FODMAP at meaningful serving sizes, because it is a galactomannan that ferments rapidly to gas in the small intestine. Many readers cutting FODMAPs assume "all gums are out" and end up unnecessarily restricting themselves further than the diet requires.
The practical upshot: at food doses, xanthan and guar are not interchangeable from an IBS perspective. We are not in a position to give clinical advice — your GP or a registered dietitian is, and Monash's app is the reference they will steer you toward.
The IBS picture above describes food-form xanthan, where the dose is fractions of a gram. At supplement-level doses above roughly 15 g per day — typical of bulk fibre supplements that use xanthan as the active ingredient — bloating, flatulence and osmotic diarrhoea are the well-documented effects. Xanthan is a soluble fibre and behaves like one in bulk.
You do not reach those doses through ordinary food intake. To consume 15 g of xanthan in a day from food alone you would need roughly 5 kg of high-xanthan dressing, which is not a meaningful scenario.
One specific population sits outside the food-dose picture and deserves its own paragraph because the published facts are unambiguous.
In 2011 the US Food and Drug Administration issued a warning about SimplyThick, a xanthan-gum-based thickener marketed for thickening infant feeds in babies with swallowing difficulties. The FDA documented cases of necrotising enterocolitis (NEC) — a serious gut condition — in premature infants born before 37 weeks gestation who had received the thickener. The FDA recommended SimplyThick should not be given to infants born before 37 weeks, and the European Food Safety Authority echoed the concern in its 2017 re-evaluation of E415.
This is a specific carve-out for the preemie / NEC context, not a general food-supply concern. Healthy adults, older children and full-term infants consuming xanthan in normal foods are not in the same risk picture. If you are caring for a premature baby and using a thickener for feeding, that is a conversation for the neonatal team, not the ingredients label.
| Property | E415 Xanthan gum | E412 Guar gum |
|---|---|---|
| Source | Bacterial fermentation (Xanthomonas campestris) | Guar bean (Indian/Pakistani crop) |
| Structure | Branched cellulose backbone with trisaccharide side chains | Galactomannan (mannose backbone, galactose branches) |
| Cold-water solubility | Disperses cleanly with mixing | Hydrates very rapidly in cold water |
| Acid stability | Stable across pH 1 to 13 | Loses viscosity in acidic foods |
| FODMAP at food doses (Monash) | Low-FODMAP | High-FODMAP |
| Mouthfeel at high concentration | Neutral, gel-like | Slightly slimy |
| Cost per kg | More expensive | Cheaper |
| Typical UK use | Dressings, sauces, GF baking, ice cream | Plant milks, ice cream, GF baking, ready meals |
The two are often used together because their strengths are complementary — guar for bulk water-binding, xanthan for elasticity and survival in acidic or hot environments.
EFSA (UK and EU). The European Food Safety Authority assigns xanthan gum an Acceptable Daily Intake of "not specified", the regulatory shorthand for quantum satis — use at the level needed to do the technical job, no numerical cap. EFSA's 2017 re-evaluation reaffirmed this for general food use and flagged the premature-infant context separately.
FDA (United States). Xanthan gum is classified as Generally Recognised As Safe (GRAS) for food use, with the SimplyThick / preemie carve-out described above as an explicit exception.
UK food labelling. Must be declared on ingredient lists as "E415", "xanthan gum", "thickener: xanthan gum" or "stabiliser: xanthan gum".
If a product carries a registered vegan certification mark, the xanthan in it has been verified as plant-fed.
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