Let’s say that I am a level 10 Arcanist. I cast Deathwine two times to affect 20 potions of Cure Light Wounds, costing 1000 gp. Then, "the first necromancy spell you cast within the next minute is cast at a higher caster level", so I spend the first 9 rounds using both my Move and Standard actions to drink those Deathwines. On the 10th round, I use my Move action to drink the 19th Deathwine, and then cast a Necromancy spell with a +19 bonus to its caster level.
Since the bonuses to caster level is untyped, those bonuses should stack.
On the other hand, this sounds like really cheap cheese, allowing e.g. a level 5 Cleric to easily create an 18-HD Necrocraft if enough gold is available. Also, the spell doesn’t explicitly say that the bonuses stack.
So, how does it work?