When eaten, it doesn't restore any hunger but removes all status effects from the player, including positive ones such as Speed II. These can be very effective while battling Cockatrices as they can keep the player from dying to the poison and losing all of their items.
In the original Aether I mod, it used to temporarily remove Poison for six seconds.
In the original Aether I mod, it has no description in the Book of Lore.
White Apple's data values are:
4186 (dec), 105A (hex), 1000001011010 (bin)
Issues relating to White Apple item are maintained on the bug tracker. Report issues for White Apple there.