- "Ethyl carbamate (ethyl urethane)," found in trace amounts in umeshu and sake, is a compound that the International Agency for Research on Cancer (IARC) suggests may be carcinogenic.
- Ethyl carbamate can be produced from components in plums or as a byproduct of the fermentation process. Its concentration may increase, especially if the fruit is left steeping for a long period.
- Measures you can take at home include removing the plums as soon as the umeshu is ready, storing it in a cool, dark place or the refrigerator away from direct sunlight, and avoiding the consumption of old plums or large quantities.
- Drinking in moderation on a regular basis does not pose an immediate danger, so there is no need to worry excessively. It is important to make safe choices based on proper knowledge.
Chemical substances lurking in everyday "umeshu" — essential basics you should know
When ume season arrives, many people make homemade umeshu. We at geefee also try out a few test batches each season, and what recently caught our attention was the topic of trace substances found in umeshu and nihonshu (Japanese sake). The original source labeled the substance as "ethyl (ethylene) carbonate," but the compound actually under scrutiny is "ethyl carbamate (ethyl urethane)," which has attracted international attention. This time, rather than needlessly alarming anyone, we want to share a clear, accurate explanation and easy measures you can take at home.
What is ethyl carbamate? Its potential carcinogenicity and origins
What kind of substance is it?
Ethyl carbamate is an organic compound found in fermented foods and some alcoholic beverages. The International Agency for Research on Cancer (IARC) has classified it as "probably carcinogenic to humans (Group 2A)." Even small amounts should be avoided in cases of long-term exposure or exposure to high concentrations.
Why It Happens (Mechanism of Formation)
There isn’t a single mechanism behind its formation. Compounds produced when cyanogenic glycosides—such as those in plum pits—break down, and compounds derived from urea and amino acids that arise during fermentation, can react with ethanol (alcohol) to form ethyl carbamate. It’s known to be detected relatively often in sake and fruit liqueurs (for example, umeshu), and the amounts vary depending on brewing and storage conditions and on the raw materials.
Risks and Real-World Effects of Umeshu (Plum Wine) and Sake
What about making umeshu at home?
Even homemade umeshu is no exception. If you leave the plums steeping for a long time, precursor compounds in the fruit can leach into the alcohol and gradually lead to formation of ethyl carbamate. However, actual concentrations vary greatly depending on how it’s made and stored, and there is little evidence that enjoying it in moderation on a regular basis causes immediate harm to health.
No need for excessive worry — but do stay cautious.
What we emphasize is balance. If you enjoy a small amount of umeshu (plum liqueur) once a month, there’s no need to worry unduly. On the other hand, it’s wiser to avoid habits like eating large quantities of ume fruit or drinking every day from the same jar that’s been left for years and become highly concentrated. In industry, measurements and controls are often carried out according to export standards for Western markets, and manufacturers in Japan are taking steps as well. Related information is also published by organizations such as the Japan Pharmaceutical Additives Association.
Practical Steps You Can Take at Home and Our Recommended Ways to Do Them
Tips During Work and After Completion
- Once they're finished, remove the plums promptly — the flavor transfers well within a few weeks to a few months, so we don't recommend leaving them to soak for a long time. When we actually tried this at home, we found the taste was fully developed after 3–6 months, and we were happy to store them in the refrigerator after taking them out.
- Store in a cool, dark place or in the refrigerator: direct sunlight and high temperatures accelerate chemical reactions, so keep it somewhere dark and cool.
- Avoid old plums and excessive consumption: refrain from eating plums that have been pickled for many years on a regular basis.
Other tips
- Heat treatment (such as low‑temperature sterilization or pasteurization) can alter certain precursor compounds and may suppress their formation. However, it also changes the flavor, so please consider it according to your goals.
- Adjust ingredients and alcohol strength:\ The amount of precursor compounds can vary depending on your choice of raw materials and the type of distilled spirit used. When choosing commercial products, it's also a good idea to check published information and opt for a reputable manufacturer.
Regulations, Standards, and Our Approach
In many Western countries, particularly when products are intended for export, concentrations of substances like ethyl carbamate are tightly controlled, and manufacturers here also work hard to maintain quality control. At the same time, foods made at home tend to show greater variation in how they’re managed, and that can be a concern. We believe it’s important not to be afraid of everything, but to use knowledge to broaden our choices.
For example: enjoy plum wine in moderation, remove the plums once it's finished, and don't overindulge in fruits that have been stored for a long time — these small precautions can greatly reduce the risk. Rather than avoiding everything just because it can be poisonous, our approach is "know it, deal with it, and enjoy it." It's the attitude we try to keep in mind every day.
Summary
Ethyl carbamate, which is present in trace amounts in umeshu and nihonshu, is certainly a compound to be mindful of—but with the right knowledge and simple precautions you can reduce the risk. When making umeshu at home, follow the basics: remove the plums once the liqueur is finished, store it in a cool, dark place or in the refrigerator, and avoid eating large quantities of old fruit. We actually made a few batches ourselves, and even when we removed the fruit after a short period we were satisfied with the flavor. Enjoying our food culture while also paying attention to safety—that’s the main point.
Disclaimer: The information in this article is for general informational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional before making any health-related decisions.
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