Tannic acid
A plant-derived polyphenol used to clarify wine and fruit juices by binding and precipitating proteins, and to add astringent flavour to beverages.
Tannins bind to iron in the gut, reducing how much non-haem iron the body absorbs. This matters most for people with low iron stores, pregnant women, vegetarians, and young children who rely on plant-based iron sources.
What is it?
Tannic acid is a hydrolysable polyphenol extracted from plant sources such as Tara pods, oak bark, sumac leaves, and gallnuts. It is a mixture of galloyl glucose esters rather than a single compound. In nature, tannins are the molecules responsible for the dry, puckering sensation in strong tea, red wine, and unripe fruit. The INS code 181 is assigned to it under the Codex Alimentarius international system, though in EU and UK food law it is classified as a food ingredient rather than a food additive, and it does not appear on the UK FSA approved-additives list.
What does it do?
Tannic acid binds to proteins, causing them to precipitate out of solution. In winemaking and juice processing, this removes haze-forming proteins and excess polyphenols, clarifying the liquid. In the gut, the same binding mechanism captures non-haem iron (the form of iron from plant foods), wrapping it in an insoluble complex that the body cannot absorb. Tannic acid also contributes colour and astringent flavour to beverages.
Where you will see it
Used as a clarifying and stabilising agent in wine production under UK and EU oenological regulations. Also used in the clarification of apple juice, beer, and other fruit beverages. In the US, permitted as a flavouring and processing aid in baked goods, confectionery, and alcoholic drinks. On wine or juice labels, it may appear as 'tannins', 'tannic acid', or in the US context 'E181'. Because it is used as a processing aid and largely removed during production, it may not always appear in an ingredient list.
What the science says
Iron absorption: well-established inhibition in human studies
Tannins form insoluble complexes with non-haem iron in the gut, preventing absorption. Polyphenol-rich beverages such as tea and coffee have been shown to reduce non-haem iron absorption significantly in human studies. The effect is dose-dependent and is most relevant when iron-rich plant foods and tannin-containing drinks are consumed together. Vitamin C consumed at the same meal can counteract the effect.
Polyphenol-containing beverages significantly inhibited non-haem iron absorption in human subjects. Tea and coffee reduced absorption in controlled feeding experiments.
Single-meal studies consistently show that hydrolysable tannins including tannic acid reduce non-haem iron bioavailability, though long-term population studies show a less clear effect on iron status.
High doses of tannic acid in rats (more than 10g per kg diet) reduced iron absorption and caused anaemia, while lower doses showed no measurable effect.
Carcinogenicity: IARC Group 3 - not classifiable
IARC evaluated tannic acid and tannins in 1976 (Monograph Volume 10) and re-evaluated them in 1987 (Supplement 7, p. 72), placing them in Group 3, meaning there is inadequate evidence to classify them as carcinogenic to humans. The Group 3 classification is the operative one, issued in the 1987 Supplement 7 update. Animal studies using subcutaneous injection produced liver tumours in rats and mice, but this route of exposure does not reflect how people encounter tannic acid in food. No adequate studies of oral administration were available when IARC assessed it, and no human epidemiological studies provided direct evidence of cancer risk from food-level exposure.
Tannic acid and tannins were classified as IARC Group 3: not classifiable as to carcinogenicity to humans. The operative Group 3 classification was assigned in Supplement 7 (1987, p. 72), updating the original Volume 10 (1976) evaluation. Animal carcinogenicity data were limited to subcutaneous injection studies; no adequate oral studies were available.
Subcutaneous injection of tannic acid produced liver tumours in rats and local sarcomas and liver tumours in mice, but the injection route is not relevant to normal dietary exposure.
Mutagenicity: no signal in standard tests
Laboratory tests in bacterial strains (Salmonella Ames test) did not find mutagenic activity from tannic acid or its related compounds, with or without metabolic activation. This is consistent with IARC's Group 3 classification.
Tannic acid and related compounds were not mutagenic in Salmonella tester strains TA98 and TA100 with or without metabolic activation in the Ames assay.
Feed safety: EFSA reviewed use in animal feed at low doses
EFSA's 2014 opinion on tannic acid as a feed flavouring (for all animal species) concluded that use up to 15mg per kg feed did not raise safety concerns at that level. This opinion addressed animal feed, not human food use, but it provides context for dose-dependence of any effects.
EFSA concluded that tannic acid used as a feed flavouring for all animal species up to 15mg per kg feed did not raise safety concerns.
Where it stands with the regulators
Who should be careful
People with iron deficiency or low iron stores, pregnant women, vegetarians and vegans relying on plant iron, and young children should avoid consuming tannin-rich drinks (tea, red wine, coffee) at the same time as iron-rich plant foods. On a wine or juice label, look for 'tannins' or 'tannic acid' in the ingredients; on many products it will not be declared because it is used as a processing aid and removed.
The honest read
Tannic acid has been in the food supply for centuries, present naturally in tea, red wine, and many plant foods at levels far higher than any residual from processing. The concern that gets the most traction in the evidence is iron absorption. Single-meal human studies show that tannins consumed alongside plant-iron foods meaningfully reduce how much iron crosses the gut wall. For most people eating a varied diet with adequate meat or fortified foods, this is a background effect. For those relying heavily on plant iron, it is a practical concern worth managing (vitamin C at the same meal helps). The carcinogenicity question was closed at Group 3 in 1987, based on injection studies in animals that tell us little about eating and drinking. There is no evidence from human populations that food-level exposure raises cancer risk. The honest state of the science is that tannins are well-characterised as iron-absorption inhibitors, mundane at food-level exposures for most people, and relevant to a specific minority.
Related additives
Common questions
Is E181 banned in the UK?
E181 is not a UK-authorised food additive E-number. It is the INS (Codex Alimentarius) number for tannic acid, which the EU and UK classify as a food ingredient rather than a food additive, so it was never included in the UK or EU approved-additives positive list. It is separately permitted for use in wine production as an oenological practice under retained EU Regulation 2019/934.
Does tannic acid in wine or tea reduce my iron absorption?
Yes, in single-meal studies, tannins consumed at the same time as non-haem (plant) iron sources meaningfully reduce how much iron is absorbed. The effect is strongest when tea or tannin-rich beverages are drunk with iron-rich plant meals. Consuming vitamin C with the same meal can substantially offset this. Long-term population studies show a less clear effect on overall iron status in people eating varied diets.
What foods contain E181 / tannic acid?
Tannic acid occurs naturally in tea leaves, red wine, unripe fruit, pomegranate, walnuts, chocolate, and some berries. As a processing aid it is used to clarify wine, apple juice, and beer, though it is largely removed during production and may not appear on the label. In the US it is also permitted as a flavouring in a wider range of packaged foods.
Is E181 vegan?
Yes. Tannic acid is extracted from plant sources such as Tara pods, oak bark, sumac, and gallnuts. It contains no animal-derived ingredients.
Sources
- UK FSA Approved Additives and E Numbers
- IARC Monographs Volume 10: Tannic Acid and Tannins (1976) - subsequent evaluation Supplement 7 (1987) Group 3, p. 72
- Hurrell RF, Reddy M, Cook JD - Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages, British Journal of Nutrition (1999)
- EFSA FEEDAP Panel - Safety and efficacy of tannic acid when used as feed flavouring for all animal species, EFSA Journal (2014)
- JECFA - Tannic acid evaluation (35th Meeting, 1989)
- Commission Delegated Regulation (EU) 2019/934 - Authorised oenological practices (tannins as clarifying and stabilising agents)
- Mutagenicity and antimutagenicity studies of tannic acid and its related compounds, Food and Chemical Toxicology (2000)
- The Impact of Tannin Consumption on Iron Bioavailability and Status: A Narrative Review, Current Developments in Nutrition
- FDA Food Substance Profile - Tannic Acid (21 CFR 184.1097)
- Wikipedia - Tannic acid
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