Blogs are one of the most prominent means of communication on the web. Their content, interconnections and influence constitute a unique socio-technical artefact of our times which needs to be preserved. The BlogForever project has established best practices and developed an innovative system to harvest, preserve, manage and reuse blog content. This paper presents the latest developments of the blog crawler which is a key component of the BlogForever platform. More precisely, our work concentrates on techniques to automatically extract content such as articles, authors, dates and comments from blog posts. To achieve this goal, we introduce a simple yet robust and scalable algorithm to generate extraction rules based on string matching using the blog's web feed in conjunction with blog hypertext. Furthermore, we present a system architecture which is characterised by efficiency, modularity, scalability and interoperability with third-party systems. Finally, we conduct thorough evaluations of the performance and accuracy of our system.