There was nothing in the books like this.

Enchanted things were always unreal.
Gold turned to dirt in an unenchanted atmosphere, food withered away and vanished.

But this test failed in the present case.

The spies brought samples: Father Adolf prayed over them, exorcised them, but it did no good; they remained sound and real, they yielded to natural decay only, and took the usual time to do it.
Father Adolf was not merely puzzled, he was also exasperated; for these evidences very nearly convinced him--privately--that there was no witchcraft in the matter.

It did not wholly convince him, for this could be a new kind of witchcraft.