Google Inc.’s most recent change to how it ranks natural search results promises to make new and updated content on e-commerce sites even more important for online retailers.

Google this week said it would change its search algorithm in order to give consumers “fresher” content in search results, according to Amit Singhal, the Google fellow who announced the move in a blog post. The change affects 35% of search results, Singhal says. That is significantly higher than Google’s Panda update, a ranking algorithm change introduced in February aimed at rewarding what Google considered high-quality web sites, and which Google said affected 12% of search results.

This week’s announcement focused on how the ranking changes will affect news and events obtained through search results, but the revised algorithm also is designed to help shoppers find the latest product information, Google says. “For example, if you’re researching the best SLR cameras, or you’re in the market for a new car and want a Subaru Impreza review, you probably want the most up-to-date information,” Singhal writes.

Search experts this week encouraged retailers to adjust with the Google changes by finding ways to put fresh content onto their e-commerce sites. “Merchants should rethink both their own product descriptions and also make sure that user reviews are happening whenever possible, especially when they are good reviews,” says Kevin Lee, CEO of search marketing firm Didit.

Unclear is exactly how Google’s web crawling technology will label e-commerce content as stale. But merchants can’t afford to take any chances, Lee says. He advises retailers to update content, and to start the effort with best-selling products and pages that already rank high in search results. “A balanced approach will be to add user reviews to existing content and rotate new reviews in regularly,” he says.

Google didn’t address how the algorithm change will work with updates delivered through social media, including Twitter, through which retailers can communicate information about deals, sales or brand issues. Barry Schwartz, news editor of the Search Engine Land blog, wrote this week that Google cannot crawl Twitter fast enough to keep up with all the messages delivered via that channel. “Google is only introducing a ranking change, not an indexing change that brings in more tweets,” he writes.

Still, that doesn’t mean retailers are off the hook when it comes to social media, another search expert says. “The ‘freshness algorithm’ is Google’s attempt to continue to provide more relevant, real-time results for search queries, further highlighting the need for marketers to accelerate their focus on integrating SEO and social marketing practices to ensure pertinent, up-to-date content is accessible to Google,” says Todd Friesen, director of SEO at Performics, an online marketing firm.

Besides participation in social networks, retailers hoping to keep ahead of the Google changes will want to invest in such marketing services as price optimization—technology that can help a retailer better compete with competitors’ offers—and display ads based on consumers’ behavior, says Eric Best, CEO of Mercent Corp., which helps retailers sell online through marketplaces and comparison shopping engines. “The more frequently a retailer can update ads, price and offers, the more relevant it will be to consumers searching through Google,” he says.

Whatever the effects of the algorithm change over the next few months, retailers hoping to keep up or improve their rankings are unlikely to earn those rewards if their pace proves too slow. After all, Google made its recent ranking change after the completion last year of its Caffeine web indexing system. According to Google, the Caffeine system enables its crawling technology to take in the web in smaller bites than the previous system, resulting in quicker updates to its search index.

“Not only is it fresher, it’s a robust foundation that makes it possible for us to build an even faster and (more) comprehensive search engine that scales with the growth of information online, and delivers even more relevant search results to you,” said Google software engineer Carrie Grimes when Caffeine was introduced.

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