E-numbers / Other additives / E920
also: L-cysteine hydrochloride · L-cysteine monohydrochloride · Cysteine
An amino acid used to soften dough in industrial bread-making. It is often made from duck feathers or pig bristles, so it may not suit vegans, vegetarians or religious diets.
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Wheat Flour [ Wheat Flour, Calcium, Folic Acid, Iron, Niacin, Thiamin], Water, Rice Flour, Rapeseed Oil, Yeast, Salt, Flour Treatment Agents (Ascorbic Acid, L-Cysteine), Dextrose.
E920 is often made from duck feathers, pig bristles or goose feathers.
300
of the 43,325 UK supermarket foods we checked declare E920 in their ingredients
That is 0.7%, counted by its code or its name.
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
Why it’s worth knowing. E920 is often made from duck feathers, pig bristles or goose feathers. Vegans, vegetarians, and people keeping halal or kosher cannot assume it suits them without asking the maker. Versions made by fermentation exist but are not always used.
L-cysteine is a sulphur-containing amino acid, one of the building blocks of protein. For food it is made in one of two ways: extracted from animal by-products such as poultry feathers and pig bristles, or made by bacteria fed on plant starch. Making it from human hair is banned in the EU and UK.
It softens dough. It breaks the links that hold gluten proteins together, which makes dough stretchier. That cuts mixing time, saves energy and gives a softer dough that runs well through machines at high speed. That is why large industrial bakeries use it.
Mainly factory-made sliced bread, rolls, pizza bases, crackers and bread improvers, and some cereal snacks and savoury pastries. UK labels call it flour treatment agent (E920), L-cysteine hydrochloride or E920. It can also be used as a processing aid, and then it may not appear on the label at all.
The traditional way to make L-cysteine is to break down animal material rich in keratin, mainly duck and goose feathers and pig bristles, with acid. The result is chemically the same as L-cysteine from any source, but its animal origin rules it out for vegan, vegetarian, halal and kosher diets. A fermentation route using plant starch exists and is growing, but makers do not have to say which method they used.
L-cysteine sold to the food industry mostly comes from poultry feathers and animal hair broken down with acid. Fermentation from corn starch exists as an alternative.
Human hair is not allowed as a raw material for L-cysteine under EU and UK food law.
L-cysteine is one of the 20 standard amino acids and is naturally in meat, eggs, dairy and many plant foods. The amount eaten through bread is very small. European reviewers set no numerical daily limit, treating it as a normal part of the diet at the levels used. No cancer, DNA damage or reproductive concern has been found at food levels.
Reviewers noted L-cysteine is a natural amino acid and set no numerical daily limit for its use as a flour treatment agent.
Under UK and EU law, flour treatment agents can sometimes count as processing aids rather than additives, if they do nothing in the finished food. When that applies, E920 does not have to appear on the label. So people who need to avoid it for diet or religious reasons cannot always spot it from the label.
E920 is allowed as a flour treatment agent and may be used without being listed when it meets the rules for a processing aid.
Daily limit. None set.
Vegans, vegetarians, and people keeping halal or kosher should know E920 is often made from animal by-products such as poultry feathers and pig bristles. The label will not always say where it came from, so ask the maker. Look for E920, L-cysteine or flour treatment agent on ingredient lists.
There is no debate about L-cysteine's health effects at food levels. It is a normal amino acid in the diet, and regulators have not found a concern at the amounts in bread. The live issue is where it comes from. Most commercial L-cysteine still comes from animal keratin, and labels do not have to say which source was used. Vegan versions made by fermentation exist, but without asking the maker there is no way to know. For people whose diet or faith rules out animal ingredients, the uncertainty is real and the label cannot settle it.
No. E920 is approved in the UK as a flour treatment agent. The only restriction is that it cannot be made from human hair. Poultry feathers and fermentation are both allowed.
Not in the UK or EU, where making it from human hair is banned. But it may come from duck or goose feathers, pig bristles, or bacterial fermentation, and makers do not have to say which.
Mainly factory-made sliced bread, rolls, pizza bases, crackers and bread improvers, and some savoury pastries and cereal snacks. It is sometimes used as a processing aid, and then it will not appear on the label.
Not reliably. Made by fermentation from plant starch it is vegan, but the traditional and still common method uses duck or goose feathers or pig bristles. Labels rarely say which, so vegans and vegetarians need to ask the maker.
Last reviewed: 20 June 2026
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