Search results, like warm cookies right out of the oven or cool refreshing fruit on a hot summer’s day, are best when they’re fresh. Even if you don’t specify it in your search, you probably want search results that are relevant and recent.

If I search for [olympics], I probably want information about next summer’s upcoming Olympics, not the 1900 Summer Olympics (the only time my favorite sport, cricket, was played). Google Search uses a freshness algorithm, designed to give you the most up-to-date results, so even when I just type [olympics] without specifying 2012, I still find what I’m looking for.

Given the incredibly fast pace at which information moves in today’s world, the most recent information can be from the last week, day or even minute, and depending on the search terms, the algorithm needs to be able to figure out if a result from a week ago about a TV show is recent, or if a result from a week ago about breaking news is too old.

We completed our Caffeine web indexing system last year, which allows us to crawl and index the web for fresh content quickly on an enormous scale. Building upon the momentum from Caffeine, today we’re making a significant improvement to our ranking algorithm that impacts roughly 35 percent of searches and better determines when to give you more up-to-date relevant results for these varying degrees of freshness.
  • Recent events or hot topics. For recent events or hot topics that begin trending on the web, you want to find the latest information immediately. Now when you search for current events like [occupy oakland protest], or for the latest news about the [nba lockout], you’ll see more high-quality pages that might only be minutes old. 
  • Regularly recurring events. Some events take place on a regularly recurring basis, such as annual conferences like [ICALP] or an event like the [presidential election]. Without specifying with your keywords, it’s implied that you expect to see the most recent event, and not one from 50 years ago. There are also things that recur more frequently, so now when you’re searching for the latest [NFL scores], [dancing with the stars] results or [exxon earnings], you’ll see the latest information. 
  • Frequent updates. There are also searches for information that changes often, but isn’t really a hot topic or a recurring event. For example, if you’re researching the [best slr cameras], or you’re in the market for a new car and want [subaru impreza reviews], you probably want the most up to date information. 
There are plenty of cases where results that are a few years old might still be useful for you. [fast tomato sauce recipe] certainly saved me after a call from my wife reminded me I had volunteered to make dinner! On the other hand, when I search for the [49ers score], a result that is a week old might be too old.

Different searches have different freshness needs. This algorithmic improvement is designed to better understand how to differentiate between these kinds of searches and the level of freshness you need, and make sure you get the most up to the minute answers.

Update 11/7/11: To clarify, when we say this algorithm impacted 35% of searches, we mean at least one result on the page was affected, as opposed to when we've said noticeably impacted in the past, which means changes that are significant enough that an average user would notice. Using that same scale, this change noticeably impacts 6 - 10% of searches, depending on the language and domain you're searching on.

(Cross-posted on the Inside Search blog)