Check Source RequiredCategory: additive, e-number, processedReviewed: Aug 24, 2026

L-Cysteine

L-Cysteine (E920/E921) is a semi-essential amino acid used as an industrial dough conditioner to relax gluten networks. Historically and commercially, the majority of global L-cysteine is extracted through acid hydrolysis of duck and poultry feathers or hog hair from slaughterhouses. Although modern microbial fermentation (bacterial biosynthesis) and synthetic routes exist, food ingredient labels almost never disclose the raw biological source without third-party vegan certification.

Vegan Status Breakdown

L-Cysteine (E920/E921) is a semi-essential amino acid used as an industrial dough conditioner to relax gluten networks. Historically and commercially, the majority of global L-cysteine is extracted through acid hydrolysis of duck and poultry feathers or hog hair from slaughterhouses. Although modern microbial fermentation (bacterial biosynthesis) and synthetic routes exist, food ingredient labels almost never disclose the raw biological source without third-party vegan certification.

Biological Origin & Animal Source:

Duck and goose feathers, hog hair, or human hair

Common Synonyms, E-Numbers & Trade Names:

e920e921l-cysteine hydrochloridecysteine monohydrochloridedough conditionerflour treatment agent

Hidden & Derivative Names to Watch Out For:

e920e921l-cysteine monohydrochloridecysteine hydrochloride anhydrousflour treatment agent (920)

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Common Uses & Applications

•Dough relaxer and conditioning agent in fast-food hamburger buns, pizza crusts, and commercial sandwich breads
•Flavor enhancer in savory processed seasonings and artificial meat aromas
•Pharmaceutical mucolytic agent (acetylcysteine / NAC)
•Cosmetics and hair conditioning formulations

Nutrition Facts (per 100g)

Standard reference data via USDA FoodData Central

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400

Calories (kcal)

100g

Protein

0g

Carbohydrates

0g

Total Fat

0.9g

Dietary Fiber

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Scientific & Regulatory Authority Sources:

Frequently Asked Questions

Why is L-cysteine used in commercial bread making?
L-cysteine functions as a reducing agent that breaks disulfide bonds in wheat gluten proteins, making high-speed industrial dough softer, more pliable, and easier to mold without tearing during rapid automated baking.
Is synthetic or vegan L-cysteine available?
Yes. Companies like Wacker Chemie produce 100% vegan L-cysteine via non-GMO bacterial fermentation from plant starch and inorganic salts, but unless a bread brand is certified vegan, the default source is typically poultry feathers.
How can vegans avoid animal-derived L-cysteine?
Look for breads labeled 'Certified Vegan', choose organic breads (where E920 is prohibited by USDA organic standards), or select artisan sourdough loaves made with only flour, water, salt, and yeast.