winnow

winnow Hide phonetics
verb [T]
1 to blow the chaff (= the outer coverings) from grain before it can be used as food

2 FORMAL to reduce a large number of people or things to a much smaller number by judging their quality:
A list of 12 candidates has been winnowed down to a shortlist of three.
a winnowing process

(from Cambridge Advanced Learner's Dictionary)

The process of determining what to finance was not easy, said Jacquelline Fuller, the head of advocacy at Google.org. Beginning in the spring of 2007, “the 20 team members had 20 ideas.” Team members, she said, “debated, cried and held hands as we tried to determine what kind of difference we could make.” It took them almost a year to winnow down the list. Although it was just announcing its initiatives on Thursday, Google.org has already begun to give away some of its money.