What is E921?
E921 is L-cystine, a flour treatment agent. Same doubt as E920.
Also written as: INS 921, E-921, E 921. INS is the international numbering system used outside Europe, including on labels in Asia, Australia and the Middle East.
What to do
Look for a halal logo, a "vegan" label, or a stated plant source on the pack. If none of these are present, you can contact the manufacturer and ask for the source.
Frequently asked questions
Is E921 halal?
E921 (L-cystine) is doubtful (mushbooh). Same doubt as E920.
What is E921 made from?
Same sources as L-cysteine.
What is E921 used for?
E921 is used as a flour treatment agent, typically in bread, rolls and bakery products.
What should I do if a product contains E921?
Look for a halal logo, a "vegan" label, or a stated plant source on the pack. If none of these are present, you can contact the manufacturer and ask for the source.
Related E-numbers
Last reviewed 2026-10-06. How we decide · Suggest a correction