Board Thread:Episode Discussion/@comment-34633327-20171118002715/@comment-5426254-20171119002841

The Grimm WOR states that by being held captive in long periods of time causes them to die off. Hell, here's a passage on the Grimm page on this very wiki itself:

Also of interesting note is that Grimm usually die off when in captivity (if they cannot kill their captors or escape first), implying that they cannot be kept alive by normal means. If the theory of Grimm not needing to feed is true, it is entirely possible that they survive on negative emotions or the act of killing in itself.

And even if they don't need emotions, don't they need to kill something or consume something tangible? So either way, the fact that destroying everything includes their food supply means that my point still stands.