Actually, both Champions Powers and the Hero System Grimoire have powers that create food and water from nothing at all by using ' Life Support (Diminished
Eating: no need to eat or drink), Usable Simultaneously', going as far as saying they can divide the food as they see fit (with GM's permission of course. So I believe Lucius' build and reasoning is actually correct.
Also Grimoire has a power called 'Putrify' built as 'Minor Transform 3d6 (edible food and drink to spoiled food and drink, heals back through another application of this spellor another appropriate spell)' that I believe can be tweaked for the OP's purpose. The relevant part to determine quantity is: