One of the biggest mysteries in the history of beer concerns a drink called three-threads, and its exact place in the early history of porter. Three-threads was evidently a mixed beer sold in the alehouses of London in the time of the last Stuart monarchs, William III and his sister-in-law Anne, about 1690 to 1714. For more than 200 years, it has been linked with the development of porter: but the story that said porter was invented to replace three-threads was written eight decades and more after the events it claimed to record, and the description that the “replaced by porter” story gave of three-threads early in the 19th century does not match up with more contemporary accounts of the drink from the late 17th century.
So what exactly was three-threads? Well, I now believe that enough people have dug out enough information that we can make a firm and definitive statement on that.