Ethyl Carbamate (Urethane) Formation in Wine and Fortified Wines

Ethyl carbamate, also known as urethane, is an organic compound with the molecular formula CH3CH2OC(O)NH2. It is the ethyl ester of carbamic acid and appears as a colorless, crystalline solid that is readily soluble in both water and ethanol. It is not an additive and is not introduced intentionally into wine; rather, it forms naturally as a byproduct of fermentation chemistry. It occurs at trace levels in a wide range of fermented foods including bread, soy sauce, yogurt, and beer, but alcoholic beverages, especially distilled spirits and fortified wines, present the highest concentration risk. IARC reclassified ethyl carbamate as a Group 2A substance, meaning it is probably carcinogenic to humans, in 2007, based on animal studies demonstrating tumor development across multiple organ sites.

• Molecular formula: CH3CH2OC(O)NH2; it is the ethyl ester of carbamic acid, not a component of polyurethane materials
• Colorless, odorless, and tasteless in wine; no sensory warning is possible at any wine-relevant concentration
• Classified by IARC as Group 2A, probably carcinogenic to humans, since 2007
• Found at low levels in bread (around 2 ppb) and soy sauce (up to 20 ppb), but alcoholic beverages can reach substantially higher levels

In wine, the dominant ethyl carbamate formation pathway begins with arginine, one of the most abundant amino acids in grape must. Yeast takes up arginine and catabolizes it via arginase, producing urea and ornithine as byproducts. When intracellular urea accumulates beyond a critical threshold, yeast exports it into the wine matrix, where it reacts slowly and non-enzymatically with ethanol to form ethyl carbamate. Citrulline, produced both as an intermediate in yeast arginine metabolism and by lactic acid bacteria during malolactic fermentation via the arginine deiminase pathway, also reacts with ethanol and is a recognized secondary precursor. Crucially, fortified wines face amplified risk: the addition of grape spirit at peak urea production causes yeast cells to release additional intracellular urea and precursor compounds into the high-ethanol medium. Storage temperature drives the reaction rate dramatically; studies confirm formation rate increases exponentially with temperature, making cool storage the most practical protective measure.

• Arginine catabolism by Saccharomyces cerevisiae via arginase is the primary source of urea in wine; urea is then excreted when intracellular concentrations exceed the yeast's capacity to reabsorb it
• Citrulline, formed by yeast and by lactic acid bacteria during malolactic fermentation, is a recognized secondary precursor that also reacts with ethanol
• Fortification at peak urea production increases precursor release; the timing of spirit addition is therefore a critical control point for Port and Madeira styles
• Storage temperature is the single most important variable governing formation rate; storage above 24°C (75°F) with urea above 5 mg/L should be avoided

Fortified wines carry the greatest ethyl carbamate burden in the wine category, driven by three converging factors: elevated ethanol content that favors the urea-ethanol reaction, the practice of arresting fermentation at the point of peak yeast urea production, and extended barrel aging under warm cellar conditions. Distilled spirits, particularly stone-fruit brandies containing cyanogenic glycoside-derived precursors, typically contain the highest concentrations of any beverage category, with some reaching thousands of micrograms per liter. Within wine, surveys confirm that whiskey, brandy, and fortified wines consistently show higher concentrations compared to table wine. Still dry wines stored at cool temperatures contain relatively low concentrations, typically well below the voluntary 15 μg/L U.S. table wine target. Grapevines heavily fertilized with nitrogen produce grapes with elevated arginine content, increasing urea production potential during fermentation regardless of wine style.

• Fortified wines, including Port, Sherry, and Madeira, carry elevated ethyl carbamate risk due to fermentation arrest at peak urea production combined with high-ethanol aging
• Grapes from heavily nitrogen-fertilized vineyards accumulate more arginine, raising urea production potential during fermentation
• Still table wines stored cool and consumed young typically fall well within voluntary targets of 15 μg/L (U.S.) or 30 μg/L (Canada)
• High-sugar musts that undergo prolonged fermentation under nitrogen-stressed conditions produce more urea, elevating risk in all high-sugar wine styles

Winemakers have several evidence-based tools to minimize ethyl carbamate formation. In the vineyard, limiting nitrogen fertilization helps prevent excessive arginine accumulation in grapes, the root cause of elevated urea in wine. Arginine levels in juice should ideally remain below 1000 mg/L. During fermentation, selecting yeast strains known for low urea excretion reduces the primary precursor load; strains such as 71B (Lallemand) and Prise de Mousse have been shown to release relatively low urea levels. For malolactic fermentation, using known commercial strains with characterized arginine metabolism avoids spontaneous inoculation by undefined bacteria that may produce citrulline. Post-fermentation, acid urease enzyme treatment can hydrolyze residual urea to ammonia and carbon dioxide; while approved and commercially available, its efficacy is significantly limited by wine's low pH and ethanol content. Temperature control during storage and transport remains the single most practical protective measure for any wine style.

• Limit vineyard nitrogen fertilization to avoid high arginine concentrations in must; juice arginine above 1000 mg/L significantly raises ethyl carbamate risk
• Select low-urea-producing yeast strains; strains differ substantially in urea excretion and reabsorption during fermentation
• Use defined commercial malolactic bacteria strains to prevent citrulline production by undefined lactic acid bacteria
• Acid urease enzyme treatment post-fermentation can reduce urea levels, but its activity is inhibited by wine's low pH, high ethanol, and malic acid content; monitor each treatment for effectiveness

Canada was the first country in the world to establish maximum levels for ethyl carbamate in alcoholic beverages, setting 30 μg/L for table wines and 100 μg/L for fortified wines. In 2025, Health Canada proposed formally transferring these limits into binding regulatory legislation under the Food and Drug Regulations, confirming the limits remain protective and achievable. The U.S. wine industry agreed in 1988 to voluntary targets of 15 μg/L for table wines and 60 μg/L for fortified wines; the FDA collaborates with industry but has not established a federal regulatory maximum for wine. In 1997, UC Davis published an Ethyl Carbamate Preventative Action Manual in cooperation with the FDA and the Wine Institute, providing practical guidance to producers. The OIV has not set maximum limits but recommends that member states adopt practices to minimize ethyl carbamate formation. No global consensus limit currently exists, creating compliance complexity for producers exporting to multiple markets.

• Canada: 30 μg/L for table wines, 100 μg/L for fortified wines; limits established in the 1980s and confirmed protective in Health Canada's 2022 reassessment
• United States: voluntary industry targets of 15 μg/L for table wines and 60 μg/L for fortified wines, adopted in 1988; no federal regulatory maximum for wine
• OIV recommends minimization practices but has not established binding maximum levels for ethyl carbamate in wine
• UC Davis Ethyl Carbamate Preventative Action Manual (1997), developed with the FDA and Wine Institute, remains a key industry reference for practical reduction strategies

Ethyl carbamate is organoleptically imperceptible at all concentrations found in wine. It produces no detectable aroma, flavor, or visual change, making it entirely invisible to the taster and the consumer. This creates a genuine food safety challenge: a wine can accumulate significant ethyl carbamate concentrations with no sensory signal whatsoever. The winemaker's practical dilemma lies in balancing protective measures against stylistic authenticity. Reducing vineyard nitrogen, choosing low-urea yeast strains, timing fortification carefully, and controlling storage temperature are all compatible with high-quality winemaking and do not measurably alter wine style. However, significantly shortening barrel aging time or radically cooling traditional warm cellars may compromise the oxidative development and flavor complexity central to premium aged tawny Port, Oloroso Sherry, or Madeira. Modern winemaking increasingly favors integrated approaches: informed vineyard nutrition, strain selection, careful fortification timing, cool temperature storage, and GC-MS monitoring to track formation rates throughout aging.

• Ethyl carbamate is colorless, odorless, and tasteless; no sensory detection is possible and analytical monitoring by GC-MS is required
• Preventive vineyard and cellar practices, including nitrogen management and yeast strain selection, do not compromise wine quality or style
• For long-aged fortified wines, a tension exists between health-protective storage conditions and the warm-cellar oxidative aging central to traditional style
• No major wine market currently requires ethyl carbamate disclosure on labels; transparency is voluntary and uncommon