NEW YORK ( TheStreet) -- Green Mountain Coffee Roasters ( GMCR) shares got a caffeinated wake-up call from Starbucks ( SBUX) on Friday after the Seattle coffee giant announced plans to roll out the "Verismo," a direct challenger to the popular Keurig machines.Green Mountain shares were trading at $52.22, down $10.18, or 16.3% at midday Friday. Starbucks shares were up $1.19, or 2.4% to $51.56. Green Mountain shares, which have a 52-week range of $39.42 to $115.98, had been steadily recovering after falling below $40 in the fall. But the Verismo is the second piece of bad news for Green Mountain in six months. The shares took a hit in October when noted short-seller David Einhorn revealed he was betting against the company over questions about its issuance of stock, its expenditures and how it had accounted for past acquisitions. The secret of Green Mountain's success has been the single-serving "pod" brewing machine, the Keurig. The Waterbury, Vt., company also distributes Starbucks coffee for use in the Keurig, which is popular at homes and in offices.