What are the signs of a watermelon past its best? Last week I bought a watermelon, and that day cut the rind of it. Also that day it was placed in a glass container, with a plastic lid that fits snugly around the glass on top, and stored in the refrigerator.

Today I went to finish it off, after not eating some for a few days, and was greeted by a 1/4 inch of milky white colored watery liquid in the bottom of the container, along with partly mushy watermelon innards.

I don't intend to eat it, but have had slightly mushy watermelon innards before, without the liquid described above. Anyone have any ideas what that is?

Additionally, what are other signs an already-cut watermelon is past its best (but not spoiled)?
It sounds like your water melon simply spoiled in the refrigerator.  It is a very perishable food, once the rind is cut off, as it is basically a sugar syrup waiting to be eaten by whatever comes along&mdash;people, dogs, bacteria, yeasts, molds, whatever.

The milky liquid would be waste from the metabolization processes of whatever colonized the water melon.

You are probably wise not to eat it; just discard it.



Some signs of past-prime watermelon include--but all of these border on signs of spoiled, because it is a continuous process:


Aroma:  If you detect an alcoholic, winy, or boozy smell, it is a sign the flesh has started to ferment. 
Another sign is when the rind is not taught and firm.
The melon is light for its size, indicating it may have lost moisture