Farmers in Vietnam's main coffee-growing province Daklak sold coffee beans  COFVN-DAK at 36,000-37,000 dong ($1.58-$1.63) per kg, lower than last week's range of 37,300-37,600 dong, and tracking a decline in London prices, traders said.

The London ICE March futures contract  LRCc3 fell as low as $1,686 a tonne on Tuesday, the weakest for the third position since June 2016.

Traders said 5 percent black and broken grade 2 robusta  COFVN-G25-SAI was quoted at a discount of $50-$75 per tonne to the ICE March futures contract  LRCc3, compared to a discount of $65-$75 per tonne a week earlier.

Weather is supporting the current harvest in Vietnam's coffee belt region of Central Highlands, ensuring supply, but falling prices discouraged farmers and exporters from selling too many beans, while buyers were also not keen, traders said.

Earlier this month, the United States Department of Agriculture revised up its forecast for Vietnam's 2017/2018 coffee crop output, including a small amount of arabica, to 29.9 million bags from a previous estimate of 28.6 million bags.

The USDA expects Vietnam's robusta output to reach 28.6 million bags for the 2017/2018 crop and exports to hit 25.5 million bags, both were adjusted higher from previous estimates.

Vietnam's coffee exports in November was revised up from a previous government estimate to 100,000 tonnes, or 1.67 million 60-kg bags, customs data showed.

Rabobank expects Vietnam's production in 2018/2019 to climb to 29.4 million bags, from 28.7 million bags in 2017/2018, while CoffeeNetwork sees a global coffee surplus of 3.7 million bags in 2018/2019, up from an anticipated 0.9 million in the prior season.

In Indonesia, the grade 4 defect 80 robusta  COFID-G4-USD was set with a $130 a tonne premium to the January contract  LRCc2, compared to a $110-$120 premium last week, a Lampung-based trader said.

Traders are only fulfilling previous contracts, the trader said, adding he expects activity to remain thin through the new year holidays as traders await the harvest season. ($1 = 22,714 dong)