Marcy Nicholson Reuters June 11, 2012 NEW YORK (Reuters) - Coffee roasters quietly pulled off a financial feat last year that went unnoticed by most customers: Adding a higher proportion of cheaper, lower-grade robusta to their grounds as the price of top-notch arabica beans surged. As new data reveals the surprising extent of that substitution, which appears to have been far more widespread than experts had thought possible, the industry faces a vexing question: As the price premium for arabica beans returns to historically normal levels, will roasters switch back? The short answer seems to be no. The "swing" in demand was surprisingly decisive and swift. U.S. robusta imports rose by almost 80 percent in the first quarter of this year versus a year ago, while arabica fell by close to a third, International Coffee Organization data shows, likely reflecting purchases made during last year's rally. "What we're realizing is that everybody ...