UBS analyst Keith Siegner says Starbucks (SBUX) is seeing accelerating momentum in the single-serve cup category. The company's K-cup sales increased 36% year-over-year for the four-week period ended August 8, according to Nielsen (NLSN), Siegner tells investors in a research note. Starbucks' K-cup promotion levels ticked up sequentially, but remain well below levels from earlier in the year, the analyst points out. The company's K-Cup portfolio continues to gain share despite increasing price pressure and new market entrants like Dunkin' Brands (DNKN) and McDonald's (MCD), Siegner writes. He keeps a Buy rating on Starbucks with a $63 price target. The stock closed yesterday up 9c to $57.83. Shares of Keurig Green Mountain (GMCR) are down 62% year-to-date in part due to the company's slowing sales in the single-serve cup category.