Recently a short video showing foam coming out of a watermelon ("foaming" watermelon) has been circulating in the social media. This raised public concerns on whether it is safe to eat such watermelons. The Centre for Food Safety (CFS) has looked into such situation, including consulting relevant experts for their opinions.
The phenomenon of "foaming" watermelon has been reported in Hong Kong as well as in other places. Experts in this area considered that when a watermelon becomes over-matured and/or is fermenting, the pressure inside the watermelon increases and this may result in the "foaming" phenomenon. On the other hand, there is currently no scientific literature documenting that "injection" to watermelon caused " foaming" of watermelon.
If "foaming" is observed in a watermelon, it is possible that the watermelon is already starting to rot. For the sake of prudence, the CFS advises the public not to eat a watermelon which is "foaming" and shows dubious quality (e.g. off odour).