Asia Cocoa-Market flat, set to remain weak in 2015 -traders

* Butter ratios at 17-month low

* Big powder stocks to weigh on prices for a year -trader

* Indonesia's cocoa bean export tax ups pressure on grinders

* Powder trading at $1,700 to $1,900 per tonne

By Fergus Jensen

JAKARTA, Dec 8 (Reuters) - Asia's cocoa market has been flat for the past week and is expected to remain depressed throughout 2015, traders said, as butter ratios hovered at 17-month lows and powder prices were weighed down by bulging grinder stockpiles.

Physical stocks of powder - used in cakes, biscuits and drinks - were still high, a Singapore based trader said, pushing prices back down to between $1,700 and $1,900 a tonne, from between $1,800 to $1,900 two weeks ago.

"The market is flat because there is a lack of market participants," the trader told Reuters. "There is no hurry to trade. People are still finding it hard to sell."

Higher-grade powder was selling for between $2,300 to $2,400 at tonne, the trader said. "It's not very exciting for grinders."

When ground, cocoa beans yield roughly equal parts of butter and powder. Grinders do not reveal the size of their butter or powder stocks.

Demand for cocoa butter, which gives chocolate its melt-in-the-mouth texture, was steady, the trader said, as global chocolate consumption has grown 1-2 percent this year.

Butter ratios, a key indicator of demand, were quoted at between 2.07 and 2.1 times London futures , their lowest level since July 2013.

Grinders were now holding between four and six months of powder stocks, a high level compared with several years ago when they only held one month's worth, the trader said.

Despite the recent growth in grinding capacity in Asia, actual cocoa grinding had slowed over the last two quarters, the trader said.

Cocoa grinding, which reflects demand for chocolate's key ingredient, dropped to 151,643 tonnes in July-September from 161,805 tonnes in April-June, according to the Cocoa Association of Asia.

"Powder stocks are actually coming down, but not fast enough. You need another year, probably, for it to come down to a level where everyone is comfortable," the trader.

The coming year is expected to be difficult for the grinding industry as pressure to reduce output will mean higher costs per tonne, another trader said.

"You need a lot of cash flow to weather this next year. Even if you are grinding less you still might have a monthly build-up of powder stocks."

Indonesia's cocoa bean export tax, unchanged at 10 percent this month, is also comparatively high for the quality of beans offered and is having a dampening effect on trade and the industry, a second trader said.

Exports of cocoa beans from Indonesia's main growing island of Sulawesi plunged 69 percent to 1,892.19 tonnes in November, from 6,038.32 tonnes a year earlier, industry data showed last week.

Indonesia is the world's third-biggest cocoa bean producer. Output from the world's top two producers may struggle to rebound from a sluggish start to the season, as several bumper cocoa crops have left trees in Ivory Coast and Ghana fatigued. (Reporting by Fergus Jensen; Editing by Pravin Char)