After the development of the large London Porter breweries in the 18th century, the trend grew for pubs to become tied houses which could only sell beer from one brewery (a pub not tied in this way was called a Free house). The usual arrangement for a tied house was that the pub was owned by the brewery but rented out to a private individual (landlord) who ran it as a separate business (even though contracted to buy the beer from the brewery). Another very common arrangement was (and is) for the landlord to own the premises (whether freehold or leasehold) independently of the brewer, but then to take a mortgage loan from a brewery, either to finance the purchase of the pub initially, or to refurbish it, and be required as a term of the loan to observe the solus tie.
In what century did the habit arise of pubs selling beer from only one brewery? (If the question is unanswerable, say "unanswerable")
18th