If you have completed March of the Dead, you can help Captain Veleth fight alcoholism amongst his people. Your task is locating the stash in which guards are hiding illegal alcohol. The task isn't very hard - it's rather obvious that they have hidden the alcohol on their usual patrol path. To find it, head out of Raven Rock and go towards the Earth Stone.
Around the middle of the road, between destroyed houses, you will find a barrel with the beverage (screen above). Open it to discover the secret and return to the quest giver to collect your prize.
Report the stash of Emberbrand Wine to Captain Veleth
You have found the illegal stash, so not go report to Captain Veleth. Speak with him (he's usually somewhere around the main square of Raven Rock). That way you will end the mission and receive a small prize in gold.