There are several online platforms that provide free or open-access textbooks, including:

If you're unable to find a free PDF download, consider the following alternatives:

: Offers a "Limited Preview" where you can search for specific terms or read snippets to determine if the book meets your needs. Google Books - Industrial Microbiology Key Topics Covered

Silas realized that a "free download" wasn't about a file on a hard drive. It was about the free exchange of foundational ideas

Perhaps the most valuable section of the book covers fermentation engineering. Casida details:

Sorry, that is a members only option