Vanilla Beans in Stout

[Miles_1111]

For a vanilal stout, people said soak vanilla beans in Vodka or bourbon whiskey for a while before add the "solution" to the beer.
1. Why needs to soak in Vodka or bourbon whiskey? Is it because beans have vegetable oil? Or just for better extacting the flavour out of the beans?
2. How long should I soak the vanilla beans in Vodka or bourbon whiskey? 3, 7 or 14 days?

Thank you very much.

 

[day_trippr]

Basically this is a tincture of vanilla bean, and commercial examples also use alcohol to solubilize the extract.
As for time, the longer the better, really.

fwiw, I use dark rum to marinade both a couple of scraped and smushed vanilla beans along with a half pound of cocoa nibs for a ten gallon batch of my imperial chocolate stout. Usually let it sit for a week in a lidded plastic container but I've let it run almost two weeks with no evident down side. The whole works gets poured into a pair of fresh carboys with the beer racked on top. I let that sit for a week or more before kegging...

Cheers!