Does dark brown color of boiled rau muong water signal chemical contamination?

April 7, 2024 | 05:00 pm PT
When I boil rau muong (water spinach) and the water turns dark brown instead of green, is this an indication that the vegetables have been contaminated with chemicals? (Lien, 33, Hanoi)


Rau muong stands out among vegetables due to its high chlorophyll content. Consequently, boiling the vegetable in an alkaline medium containing minerals such as calcium and magnesium can lead to the formation of compounds that manifest as dark green or black.

This explains why, from ancient times, people have devised techniques like incorporating lime juice or dracontomelon fruit into the boiling water for rau muong, aiming to create an acidic setting that mitigates the interaction between these compounds, thereby maintaining clearer water.

Boiled rau muong (water spinach). Photo by VnExpress

Boiled rau muong (water spinach). Photo by VnExpress

Hence, the occurrence of dark brown water during the boiling of rau muong does not automatically imply that the vegetables are laced with chemicals. Nevertheless, there exist instances where hazardous farming techniques result in chemical contamination, which could cause the water to turn a similar color upon boiling.

Determining the presence of chemicals involves careful observation. If chemicals are present, the water might emit a slightly unpleasant odor, and an oily layer might be observed floating on its surface.

Attempting to clarify the water by adding some lime juice and observing any changes could be insightful. If the addition of lime juice does not lead to clearer water or the disappearance of the oily layer, it is advisable to avoid using the water.

For safety, individuals are encouraged to opt for secure and organic vegetables, ensuring they are washed and thoroughly cooked prior to eating.

Dr. Dang Ngoc Hung

Director of the Nutrition Research and Consulting Institute

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