Depends on Source
How we decideSome routes to it require the animal to die and some do not, and the label rarely says which was used.
The two diets, side by side
A vegetarian diet excludes animals that were killed. A vegan diet excludes animal products entirely, whether the animal survived or not. L-Cysteine can fall either side of that line depending on how it was made.
L-Cysteine depends on the manufacturer. E920 is still commonly made from human hair or from duck and pig feathers, though petroleum and fermented corn routes exist and are vegan. Commercial bread and pizza dough are where you meet it, and only the bakery can tell you which source it buys.
What it is
- Comes from
- Can be derived from: (1) human hair or duck/pig feathers [not vegan], (2) petroleum byproducts [vegan], or (3) fermented corn [vegan]. Source varies by manufacturer and is rarely specified on labels.
- Which animal
- duck or chicken feathers, pig bristle, or human hair
- Requires slaughter
- Yes
- Where you meet it
- Commercial bread, pizza dough, pastries — used as a dough conditioner to improve texture and reduce mixing time.
- What replaces it
- No direct alternative. Contact the manufacturer to ask about their cysteine source.
Editorial notes
The majority of L-Cysteine commercially available is still derived from poultry feathers or human hair. Some manufacturers use synthetic or fermented plant-based cysteine — ask directly.
Frequently asked questions
Is L-Cysteine vegetarian?
Depends on Source. Some routes to it require the animal to die and some do not, and the label rarely says which was used.
Is L-Cysteine vegan?
Depends on Source. L-Cysteine depends on the manufacturer. E920 is still commonly made from human hair or from duck and pig feathers, though petroleum and fermented corn routes exist and are vegan. Commercial bread and pizza dough are where you meet it, and only the bakery can tell you which source it buys.
Is L-Cysteine vegan?
It depends on how it was produced, and the label does not say. L-Cysteine can be derived from human hair or poultry feathers, which is not vegan, or made by fermentation of plant sugars or by chemical synthesis, which are vegan. The source is rarely disclosed. To be certain, ask the manufacturer or look for a vegan certification.
Is L-Cysteine made from human hair?
It can be. One of the traditional industrial routes extracts cysteine from keratin-rich materials, including human hair as well as duck, chicken, and hog feathers and bristles. Other batches are made by fermentation or synthesis and involve no animal or human material. The finished amino acid is identical regardless of source, so the label alone will not tell you which method was used.
What foods contain L-Cysteine?
Commercial baked goods are the most common home, where it acts as a dough conditioner. Typical products include mass-produced bread, bread rolls, pizza dough, bagels, and laminated pastries. It may be listed as L-Cysteine, cysteine, L-Cysteine hydrochloride, or E920, or hidden within a general "dough conditioner" or "flour treatment agent" description.