Obtain Thunderbrew's Hard Ale and combine them with Wolvar Berries that Vekgar provided to make the secret Frenzyheart drink. Using the drink's power, slaughter 30 of the Sparktouched Gorlocs around Kartak's Hold and then speak to Shaman Jakjek.
Battle still going at Kartak's Hold... I think it time for you to learn big secret of Frenzyheart.
We have berries we keep from other lands we came from... they not so special on their own, but mix them with drunk drinks and they make Frenzyheart super strong. You a Frenzyheart now... it time you get to be strong too.
Vekgar teach you super secret, eh? Only strongest Frenzyheart get to know secret.
You a fierce fighter... come back for more battle soon. Never enough good battle!
Completing this quest is a criteria of the Honorary Frenzyheart achievement.
Go back to Nesingwary's Base Camp and ask Grimbooze for his hard ale. He will just give it to you.