Derby Day Sweepstakes! Trivia Question #2

Ok, well apparently the first question was too tough because no one even attempted to answer...  Oh well, we're raising the stakes!!  Today will be treated like a Skins Match - since no one won yesterday, today's correct trivia answer is worth TWO $25 gift certificates to Restaurant.com!!!

Ok, let's get to it...

Q: Bourbon Whiskey is made up of a mash that consists of corn, barley, rye and/or wheat.  What percentage of corn must the mash contain in order for the distillery to classify the whiskey as Bourbon?

First correct answer in the comments wins TWO $25 gift certificates courtesy of Restaurant.com!