Starbucks had an awesome quarter. It recorded record sales, earnings and margins. It is adding new units worldwide and is luring more customers. Its consumer products business is flourishing and proving wise its decision to bring the business in-house. And yet, its stock in extended trading is down 2 percent. Why? Commodities. The company said that commodity costs, mostly record coffee prices but also cocoa prices, will have a 20 cents per share impact on earnings in the year, and not in a good way. Coffee prices are near record levels, said CFO Troy Alstead on the company's quarterly conference call this afternoon. Such spikes happen, he said, but not for very long, and the company doesn't expect the price to be sustainable. "This headwind may become a tailwind in the future," he said. Nevertheless, the early reaction to Starbucks' earnings revision confirms our belief that commodities will spook investors in the coming weeks, holding down restaurant stocks.