Through careful examination I have found that in food the different Quality levels govern the three base attributes of food: "Energy", "Satiation(Hunger)" and FEP. ESV Essence regulates how much Energy the food item refills, Substance how filling it is and Vitality how many FEPs the item gives, and in food the formulae for what quality does what when crafting them are pretty simple. Ingredients with higher Vitality give the finished product higher Vitality, modified of course by the apropriate abilities and attributes.
Now, I suck at writing fancy instructional posts, but a big sticky-thread explaining the quality system in depth sounds like a good idea to me. Just because some aspects are still mysteries doesn't mean that what is known should remain in the shadows. Take stone axes for instance. Which quality determines what rocks you can mine, or how good butchered meat turn out, or how neat logs you can get? I dunno, and I can't be the only one hitting my head on a wall over this strange quality system.