The Freshness update built on Caffeine, the indexing system Google completed the year before. Google said Caffeine "allows us to crawl and index the web for fresh content quickly on an enormous scale".
On 3rd Nov 2011 it announced "a significant improvement to our ranking algorithm that impacts roughly 35 percent of searches". The change "better determines when to give you more up-to-date relevant results".
Google named three kinds of query. "Recent events or hot topics", where "you'll see more high-quality pages that might only be minutes old". "Regularly recurring events", such as annual conferences. And frequently updated topics.
The 35% figure measures searches touched, not searches changed noticeably. Google's ranking systems guide still lists freshness systems that "show fresher content for queries where it would be expected".
