Hedge fund manager David Einhorn is betting that Green Mountain Coffee Roasters will lose its buzz, pushing the company's share price down 11 percent on Monday.

Green Mountain's stock has performed well, but the company's prospects may not be as good as some people think, Einhorn said at the 7th annual Value Investing Congress.

Calling his presentation GAAP-uccino, Einhorn said that using one of Green Mountain's products which offer single serve cups is a very expensive way to drink coffee at home, while going through some 110 powerpoint slides.

He called on the company to improve its disclosures, and warned that the market for its products is smaller than people who like the stock think.

Einhorn's stock picks are closely watched ever since he was among the first to raise doubts about accounting practices at now bankrupt investment bank Lehman Brothers.

While Einhorn is worried about Green Mountain's accounting and shipping practices, the company has been a favorite with hedge fund managers such as John Thaler of JAT Capital, in part because of the rapid growth of its Keurig single-cup coffee machines. Some people have referred to Green Mountain's single-cup brew as the iPod of the coffee industry.

Between the high cost of the machine and high cost of the coffee, this is a luxury item, said Einhorn, listing the arguments on why the share price should be trading closer to $3.50 -- not roughly $9 where it is now.

Einhorn said that capital spending is rising quickly but the company is not detailing exactly where the money is going.

He also said that an inquiry by regulators, launched a year ago, into the company's relationship with a fulfillment vendor who helps sell the products to others, has not been closed.

Green Mountain shares were down 11 percent at $82.07 on the New York Stock Exchange.

Greenlight Capital, which has about $8 billion under management, is down a little more than 5 percent for the year.

(Reported by Svea Herbst-Bayliss. Editing by Matthew Goldstein, Robert MacMillan and Bernard Orr)

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