Bitter Harvest is a secondary quest in The Witcher 3: Wild Hunt and is located near the Border Post, on the Velen side of the river.
Walkthrough
To start this quest, Geralt must speak to Albin Hart who is located at the battlefield south-southeast of the Border Post, before or after talking to the shady merchant nearby. Albin will ask Geralt to defend him and his men from the necrophages drawn to the battlefield by the stench of death so his workers can loot the bodies. Accept the quest to start the waves of monsters.
Protect the scavengers
The ghouls will all come from the south-southeast part of the yellow area on your map, so your best chance if you want Albin to live is to be near this spot to prevent Albin from trying to recklessly engage the monsters. You will face 4 waves here: first two will have 3 ghouls each, the third with 2 ghouls and a rotfiend, and the fourth with 3 ghouls. Note that the last wave can spawn while you're still dealing with the previous, making it a bit more difficult.
Bandits on horseback may also be present around the southern edge of the marked area if they had not been previously killed. They belong to a nearby deserter camp denoted on the map by a person(s) in distress marker and can make this even tougher. Bandits may still spawn even after the marker has been cleared.
If Albin dies, one of the looters will pay Geralt 20 
once all the monsters in the area are defeated, and the quest will complete (earning 50 
). Note that this outcome will lead to the failure of Fake Papers if it hadn't already been completed by other means.
If Albin survived, then after the final wave go back and talk to him. After Geralt speaks to him he'll reward you 50 and 50 and the quest will complete. This outcome also qualifies you for a discount from the shady merchant on a fake pass if the pass has not yet been obtained.
Journal entry
- The Nilfgaardian and Redanian forces had fought many bloody yet indecisive battles in Velen from which both sides had to retreat without collecting their dead. On one such field Geralt encountered a group of looters robbing the corpses of the fallen. In another time and place he might have merely grit his teeth and continued on his way. Yet conditions in Velen were harsh and other sources of sustenance few - so he decided to swallow his revulsion and defend these desparate [sic] men from the monsters stalking the battlefield.
- Hiring a witcher was one of the best ideas the looters' leader had ever hit upon. Geralt dutifully kept the monsters at bay while they completed their grim harvest.
Objectives
- Protect the scavengers from monsters.
- Talk to the scavengers' supervisor.
Notes
- If Albert dies and you still need a pass, you can still do Contract: Woodland Beast or continue the quest Family Matters to the point of learning where Tamara is to obtain one.