Fresh Brewfest Hops costs 2 x Brewfest Prize Token.
If you have a Brewfest Hops buff active and want to apply a different Brewfest Hops buff, the other faction's mount, for example, the current buff blocks application of the new buff. You must manually turn off the current buff by right clicking it and dispelling it in order to apply the new buff. (Source)
The act of consuming the item awards the achievement Have Keg, Will Travel. Players do not need to own a mount, mount up, or even have trained in riding. (Note: Character must, however, be eligible to learn Riding - so character must be at least level 20.)
See also: Fresh Dwarven Brewfest Hops, Fresh Goblin Brewfest Hops.
For the permanent consumable, see Preserved Brewfest Hops.