Farmers in the Central Highlands, Vietnam's largest coffee growing area, sold coffee at 35,300 dong ($1.51) per kg <COFVN-DAK>, down from 36,200-36,300 dong a week earlier, traders said.
The London January futures contract closed at $1,615 on Wednesday, down from $1,663 a week earlier, Refinitiv Eikon data showed.
"Farmers are still making little profit at this price, but if prices fall further, they will consider slowing down sales," a trader based in Dak Lak province said.
Traders estimate that farmers have harvested nearly 40 percent of the beans and the harvest will end late-December.
"Output of the 2018-19 crop year is estimated at 30 million 60-kg bags, similar to the previous crop year," the trader said. This is higher than an earlier forecast of 27 million bags.
Coffee Network analyst Andrea Thompson said on Wednesday that there would be a global surplus for the season of around 11 million bags, putting Vietnam's forecast at 31 million bags.
Traders in Vietnam offered the 5 percent black and broken grade 2 robusta <COFVN-G25-SAI> at a $45-$65 discount per tonne to the January contract, narrowing from $70 last week.
In Indonesia, premiums for robusta beans in the province of Lampung in Sumatra rose to $50 for the January contract due to depleting stocks, from $30 last week, according to an exporter.
"Trades remain light as local inventories of robusta beans continue to fall after the harvest," the trader said.