At the Oregon National Primate Research Center in Beaverton, however, researchers finally cloned monkey embryos and derived ES cells from them in 2007. In the process, they discovered a number of tweaks that made SCNT more effective for primate cells, including human ones. The final recipe worked surprisingly well, yielding ES cells in about one in 10 tries. One key ingredient seems to be caffeine, which appears to help stabilize key molecules in the delicate human egg cells.