Have personally followed this test for Injected Watermelons and it has never failed except whenever I am not patient. This test stands for all fruits which can be injected with colors or sweeteners like apples, oranges, other melons and even tomatoes.
The first step in this test is to properly wash and scrub the fruit with Potassium Permanganate or vinegar or other such solutions to remove hydrophobic layer on the peel to cover the injection mark.
Second step is to leave the watermelon for couple of days outside in kitchen. I never eat a watermelon right after I have purchased it. If its been injected It will ferment and start oozing in 2-3 days with white smelly foam(photo). Oranges ferment even faster. For 99% of oozing cases you will observe that inside is extremely red.
Watermelon stays good inside even after several days to a month. Once I had a watermelon for two months and it was still good inside. Just be patient and wait for 2-4 days to cut open a watermelon. You will avoid lots of dangerous chemicals. So go ahead and enjoy this super cool fruit this summer. Just buy few days before you want to consume.
Coming up…..How to test Injected Apple and Orange