NEW YORK (TheStreet) -- Shares of Boston Beer  (SAM) - Get Report are plummeting, sharply down 15.97% to $261.10 in early market trading Wednesday, after the beer company had its rating lowered to "market perform" from "outperform" by analysts at Cowen this morning.

The firm also cut its price target on shares to $308 from $336, and views valuation as rich.

Cowen analysts said the downgrade reflects Boston Beer's soft 2015 guidance, as well as reduced preliminary shipment growth. 

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The firm noted that Boston Beer provided preliminary guidance for shipment and depletion growth in October of a 10% to 15% increase in 2015. But the company reduced its outlook to between 8% to 12%.

Cowen added that the company's management said 2015 will face particularly tough comparisons amid heightened competition.

Boston-based Boston Beer is a craft brewer, engaged in the business of brewing and selling alcohol beverages domestically and abroad.

The company sells beers under the Samuel Adams names as well as flavored malt beverages under the Twisted Tea brand name, hard cider beverages under the Angry Orchard brand name and more than twenty beers under four of its Alchemy & Science subsidiary's brand names.

Separately, TheStreet Ratings team rates BOSTON BEER INC as a Buy with a ratings score of A. TheStreet Ratings Team has this to say about their recommendation:

"We rate BOSTON BEER INC (SAM) a BUY. This is based on the convergence of positive investment measures, which should help this stock outperform the majority of stocks that we rate. The company's strengths can be seen in multiple areas, such as its robust revenue growth, impressive record of earnings per share growth, compelling growth in net income, expanding profit margins and good cash flow from operations. We feel these strengths outweigh the fact that the company is trading at a premium valuation based on our review of its current price compared to such things as earnings and book value."

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