Keurig Green Mountain Inc is recalling about 7.2 million single-serve brewing machines, the coffee company announced on Tuesday, warning that the machines could overheat and injure users by spraying hot liquids on them. Keurig's shares fell 2.5 percent to $136.29 in morning trading, as investors worried the recall would sow doubt about the brand as the company tries to roll out new brewers and expand beyond the single-serve coffee business.