Dimethyl dicarbonate
A synthetic liquid added to beverages just before bottling to kill yeast and bacteria. It breaks down completely before you drink the product.
What is it?
Dimethyl dicarbonate (DMDC) is a colourless synthetic liquid with a pungent odour. It is manufactured by chemical synthesis and is unrelated to any animal-derived ingredient.
What does it do?
DMDC penetrates microbial cell walls and inactivates key enzymes involved in cellular metabolism, killing yeast, bacteria and mould present in beverages. It is dosed into the drink immediately before filling or bottling, then breaks down within minutes at room temperature into carbon dioxide and methanol. Its half-life in solution is roughly 15 minutes at 20 degrees C. By the time the product reaches the consumer, no DMDC remains.
Where you will see it
Used in non-alcoholic soft drinks, fruit juices, iced teas, sports drinks, flavoured waters, energy drinks, non-alcoholic wines, and some alcoholic drinks including wines, ciders and hard seltzers. Because DMDC decomposes before consumption, it is classified as a processing aid in many jurisdictions and is not always required to appear on the ingredient list. When declared, it reads as 'dimethyl dicarbonate' or 'E242'.
What the science says
What happens to E242 in the drink
Once added to a beverage, DMDC reacts with water and dissolved substances within minutes. The main products are carbon dioxide, methanol, dimethyl carbonate, methyl ethyl carbonate and small amounts of methyl carbamate. DMDC itself is no longer detectable in the finished product. Regulators assess any residual risk from these breakdown products rather than from DMDC directly.
DMDC rapidly and fully hydrolyses in aqueous solution; the main reaction products are carbon dioxide, methanol, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC) and methyl carbamate (MC). No DMDC residue remains in treated beverages at the time of consumption.
Methanol produced from DMDC hydrolysis in beverages is in the range of approximately 50mg/L for normal treatment doses, a level far below the threshold for toxic effects. Humans already metabolise 1000 to 2000mg of methanol per day from natural dietary sources.
Genotoxicity and carcinogenicity of DMDC and its breakdown products
Genotoxicity tests on DMDC itself returned negative results across multiple assay types including the Ames bacterial mutation test. Methyl carbamate, one of the trace reaction products, was found to be non-genotoxic and non-carcinogenic in animal studies, distinguishing it from ethyl carbamate (a different compound found in fermented foods that is classified as a probable human carcinogen).
DMDC and its principal breakdown products tested negative in genotoxicity assays including the Ames test and mammalian cell mutation tests.
Methyl carbamate, a trace reaction product of DMDC in beverages, is non-genotoxic and non-carcinogenic in animal studies, unlike ethyl carbamate which is a probable human carcinogen (IARC Group 2A).
High-consumer exposure to methyl ethyl carbonate
In its 2015 re-evaluation, EFSA found that most breakdown products fall below the Threshold of Toxicological Concern (TTC) at typical consumption levels. One exception was noted: methyl ethyl carbonate (MEC) could exceed the TTC for very high consumers of DMDC-treated beverages. EFSA concluded there was no overall safety concern at current permitted use levels, but flagged this finding as worth monitoring if usage increases.
Exposure to the main reaction products of DMDC remains below the threshold of toxicological concern (TTC) with one exception: methyl ethyl carbonate (MEC) for high-level consumers. Despite this, the Panel found no indication of a safety concern from DMDC use at currently reported use levels.
Established use as a beverage sterilisation agent
JECFA, the joint FAO/WHO expert committee, evaluated DMDC and found it acceptable for use as a cold sterilisation agent in beverages when applied at up to 250mg/L under good manufacturing practice. Long-term animal feeding studies using DMDC-treated beverages showed no adverse effects on organ function or tissue health.
Rats given DMDC-treated beverages at high concentrations for up to 30 months showed no observable adverse effects on organ function or histology.
JECFA determined DMDC acceptable for use as a cold sterilisation agent in beverages at up to 250mg/L under good manufacturing practice.
Where it stands with the regulators
Who should be careful
No specific group is advised to avoid E242 by any UK or EU regulator. Because DMDC itself is absent from the finished product, allergy or intolerance to the additive itself is not a recognised clinical concern. Anyone with an existing sensitivity to methanol or who consumes very large volumes of treated soft drinks daily may wish to note that methanol is a minor byproduct, though at levels far below those associated with harm. Look for 'dimethyl dicarbonate' or 'E242' on the label if present.
The honest read
E242 is one of the more technically straightforward additives in the UK-permitted list. It does a defined job, then disappears. The science on DMDC itself is consistent across multiple decades and regulators: negative genotoxicity, no carcinogenicity signal, no endocrine concern, no allergenicity. The one live question from the 2015 EFSA review concerns a single breakdown product, methyl ethyl carbonate, which can exceed a precautionary threshold in very high consumers. EFSA did not change the permitted level on that basis, and the threshold itself is a conservative planning tool rather than evidence of harm. The science on DMDC is more settled than on most approved preservatives.
Related additives
Common questions
Is E242 banned in the UK?
No. E242 is approved for use in the UK under the UK FSA approved-additives list and assimilated EU Regulation 1333/2008, permitted in non-alcoholic beverages, non-alcoholic wine and certain alcoholic drinks at up to 250mg/L.
Does E242 remain in the drink I buy?
No. DMDC breaks down within minutes of being added to a beverage, with a half-life of roughly 15 minutes at room temperature. By the time the drink is bottled, sealed and reaches the shelf, no DMDC is present. What remains in trace amounts are its breakdown products: mainly carbon dioxide, methanol, dimethyl carbonate and methyl ethyl carbonate.
What foods contain E242?
E242 is used in non-alcoholic soft drinks, fruit juices, iced teas, sports drinks, flavoured waters, energy drinks, non-alcoholic wines, some wines, ciders and hard seltzers. Because it decomposes before consumption, manufacturers are not always required to declare it on the label, so it may not appear in the ingredient list even when used.
Is E242 vegan?
Yes. Dimethyl dicarbonate is synthetically manufactured and contains no animal-derived ingredients. It is compatible with vegan and vegetarian diets.
Sources
- EFSA ANS Panel: Scientific Opinion on the re-evaluation of dimethyl dicarbonate (DMDC, E 242) as a food additive, EFSA Journal 2015;13(12):4319
- JECFA: WHO Food Additives Series 28, Monograph 722: Dimethyldicarbonate (DMDC)
- UK Food Standards Agency: Approved additives and E numbers
- Commission Regulation (EU) No 1166/2012 extending use of E242 in alcoholic beverages
- LANXESS Velcorin: Cold sterilisation systems for beverages
- Nury et al., Formation of Methanol and Ethyl Methyl Carbonate by Dimethyl Dicarbonate in Wine and Model Solutions, American Journal of Enology and Viticulture 27(1):7
- Wikipedia: Dimethyl dicarbonate
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