I've tried the same and have several bad news:
1. Reactions can't find items stored in bags and barrels. Using meat and plants is painful, using booze and syrup is impossible.
2. Reactions do not generate quality levels.
3. Reactions ignore the directives of the 'Kitchen' screen. (What you let your dwarves use for cooking and brewing.)
4. Reactions can't create 'food'. (or at least everyone that has tried that before has failed, and that's a lot of people.)
I will be more than happy if anyone can refute any or all of these points.
1. That is correct. the only thing it can find is lye, as there is a special tag for it.
2. That is also correct.
3. That is also correct, the reaction is not considered a cooking actions so it would ignore it.
4. Not correct, I've had reactions that make 100 stack of plump helmets. Of course it never fit in a barrel, but it can this time around.
[REACTION:MAGICAL_FOOD]
[NAME:Lavish food]
[REAGENT:B:1:BARREL:NONE:NONE:NONE][EMPTY][BARREL][PRESERVE_REAGENT]
[PRODUCT:100:15:FOOD:ITEM_FOOD_ROAST:PLANT_MAT:BERRY_SUN:FOOD][PRODUCT_DIMENSION:150][PRODUCT_TO_CONTAINER:B]
[PRODUCT:100:1:BARREL:NO_SUBTYPE:PLANT_MAT:OAK:WOOD][PRODUCT_DIMENSION:150]
[BUILDING:MAGIC_SHACK:NONE]
[SKILL:SMELT]
You don't need that. [PRESERVE_REAGENT] means it wont be eaten up in the reaction.