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Is it vegan? · L-cysteine (E920)

Last reviewed August 17, 2026

Is L-cysteine vegan?

Sometimes. L-cysteine is an amino acid dough conditioner. Much of it is extracted from animal keratin such as feathers or hair, but fermentation-derived and synthetic versions are vegan, so it depends on the source.

L-cysteine softens dough and often starts as animal keratin, from feathers or hair. Fermentation-made and synthetic versions are vegan, so it genuinely depends.

Where it hides

  • Commercial bread rolls and bagels
  • Some pizza and pastry dough
  • Pretzels and other bakery goods

What it is

L-cysteine is an amino acid used in small amounts to relax dough and speed up baking, listed as E920. The chemistry is the same whatever the origin, and that origin is the whole question. A large share of commercial L-cysteine is extracted from animal keratin, historically duck and chicken feathers and human hair, while a growing amount is made by bacterial fermentation of plant sugars or produced synthetically, both of which are vegan.

Why it depends

Because the label just says L-cysteine or E920, you cannot tell the source from the packet. Some bakeries and brands now specify a plant-based or fermentation-derived version, and the honest answer is that it varies by manufacturer. If it matters to you, this is one to ask about rather than assume.

How it is made

L-cysteine is a sulphur-containing amino acid used in tiny amounts, typically 20 to 30 parts per million of flour, as a reducing agent that snips the disulphide bonds in gluten. That relaxes dough so industrial lines can sheet and shape it fast without tearing, cutting mixing and proving time. It is not there for flavour or nutrition. It is a processing tool for high-volume baking, which is why small bakeries generally have no use for it.

Historically, and still for a meaningful share of supply, it is produced by dissolving keratin-rich waste in hot hydrochloric acid: duck and chicken feathers, hog bristle, and human hair collected from barber shops. A 2011 survey of ingredient suppliers by the Vegetarian Resource Group put animal-derived sources at roughly 90 percent of the market at that time, with fermentation and synthetic routes making up the rest at two to three times the cost. No regulator or trade body has published an updated breakdown since, so treat that split as the best documented figure rather than as current fact; fermentation capacity has grown considerably in the years since.

How to tell

It appears in commercial sandwich bread, burger and hot dog buns including many fast food chains’, bagels, chain and frozen pizza dough, and pretzels. It is functionally absent from sourdough and most small-bakery bread, where slow fermentation and hand shaping already relax the gluten. On labels it reads as L-cysteine or E920 with no origin given, so vegan certification on the pack, or a brand that publicly states it uses the fermentation-derived version, are the routes that actually answer the question.

What the rules say

The FDA affirms L-cysteine as generally recognised as safe and caps its use in yeast-leavened baked goods, with no restriction on where it came from, so feather-derived cysteine meeting purity standards is legally usable in US bread. In the EU it is E920 and must be declared by name or number, because it acts as an additive rather than a processing aid. Unlike enzymes that vanish from the label under carry-over rules, its presence is never hidden. Only its origin is.

  • Bone char sugar Some cane sugar is whitened by filtering it through charred cattle bone. The sugar holds no bone, but the process is animal, so it depends on the brand.
  • Gelatin Gelatin is boiled animal collagen, usually from pig or cow skin and bone. There is no plant version; the plant swaps are agar, pectin and carrageenan.

Frequently asked

Is L-cysteine really made from hair?

Some of it is. L-cysteine has long been extracted from keratin sources including human hair and poultry feathers, though fermentation and synthetic routes that are vegan now supply a growing share. The label does not say which, so the source varies by brand.

Which foods contain L-cysteine?

It is a common dough conditioner in commercial bread rolls, bagels, pizza dough and other bakery goods. Home baking and many artisan loaves do not use it.

Is L-cysteine made from human hair?

Some of it historically was, so the claim is not an urban legend, but it is routinely exaggerated. Human hair is one of several keratin feedstocks alongside duck and chicken feathers and hog bristle, and a 2011 industry survey put all animal sources together at about 90 percent of the market at that time. Fermentation-derived cysteine has grown since.

Does all bread contain L-cysteine?

No. It is used almost entirely in industrial, high-speed bread lines, including many fast food buns, bagels and frozen pizza dough. Artisan, sourdough and most small-bakery bread does not need it, because slower fermentation already does the job of relaxing the gluten.

Is fermentation-made L-cysteine vegan?

Yes, when it is produced by feeding plant sugars to bacteria that excrete the amino acid, with no keratin anywhere in the process. The molecule is chemically identical to the hair or feather version, but the route is entirely plant-based, which is why some brands market it specifically as vegan L-cysteine.

How can I tell if a product’s L-cysteine is animal-derived?

Not from the label, in either the US or the EU, since neither requires the source to be given. Vegan certification on the pack, or a brand that states publicly that it uses fermentation-derived L-cysteine, are the only reliable routes short of asking the manufacturer directly.

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