Someone asked this question and we looked into it thoroughly.  Here is my response.

The reason I said bourbon is fine for Pesach is based on a few halachic points.

First, there is barely any actual wheat left in the final product. Whatever originally came from the grain is extremely diluted and clearly batel beshishim. In reality there is practically no physical wheat content left in bourbon.

Second, the material at that stage is not ra’ui le’achilah. The mash during fermentation becomes something that nobody would eat. That itself is a major factor.

Your argument that the flavor transfers before it becomes not ra’ui le’achilah doesn’t really make sense. If the flavor had already fully transferred at that earlier stage, there would be no reason for the producers to continue processing it through fermentation and distillation. The entire process changes the material completely.

Also, the “flavor” we are talking about here is not the kind of ta’am that Chazal refer to in tarovot. That kind of ta’am assumes there is enough substance present to matter halachically. Here the flavor is extremely indirect — more like when food is smoked with wood and people say it has a cedar or oak flavor. That doesn’t mean the wood itself is part of the food.

In addition, this is all chametz before Pesach, which is a rabbinic issue. From the Torah perspective, chametz is only prohibited when it exists as actual chametz. Here we are dealing with a processed product long after the grain has completely changed form, and the entire process happens well before Pesach.

So between batel beshishim, not ra’ui le’achilah, the very indirect nature of the flavor, and the fact that this is processed long before Pesach, there is no real halachic concern.

That’s why I’m comfortable saying bourbon is fine.