Member Services was contacted about grog and this is what they wrote back.
Thank you for your email. Grog will be one of the toughest building materials that you will loot on the seas for Ship Customization. This item will only be found on 'War' class ships, but it may take many battles before any Grog is looted.
Try your hand at battling War Sloops, War Galleons, and War Frigates and hopefully you'll be on your way to building the best Pirate ship in the Caribbean. Be sure to share this information with your Pirate friends on Test so that we can have everything ready to go when Pirates on the Live Servers are ready to customize their own ships.