Google has responded to rumours of unannounced Google Penguin updates by refusing that any have taken place. The announcement followed the release of a recent Google video which suggested that an update to Google's anti-spam filter might have taken place.
The last official Google Penguin update was confirmed in October 2012. It was the third Penguin update and took place more than four months ago. But a video published recently featured Google's John Mueller who responded to a question about updates in a way which many interpreted to mean that more regular updates did take place unannounced.
When Google was asked to comment on this they responded by saying that his comments referred to regular 'link analysis' refreshes and not refreshes of the Penguin algorithm. They furthered that there had been no updates to the Google algorithm since the one confirmed in late 2012. They also explicitly confirmed that they do not carry out regular updates in the way that they do with Google Panda updates.
While the Google Panda algorithm is now updated on a largely month to month basis, Google has not yet confirmed the next one, but a refresh is expected to hit over the next few days. Google Penguin was first updated on April 24 2012, and 3.1% of English language queries were impacted but since then there have only been two subsequent updates. One took place on 26 May 2012 and affected less than 0.1% of English language search queries. The second was the 5 October 2012 update which affected just 0.3% of English language search queries.