Complex sentence: Mechanical filtering and even pasteurisation of bottled beer started at the end of the 19th century, though the first beer known to have been mechanically filtered and force carbonated as draught keg beer was "Watneys Red Barrel" in 1931.
Split into simpler sentences: Mechanical filtering and pasteurisation of bottled beer started at the end of the 19th century. The first beer known to have been mechanically filtered and force carbonated as draught keg beer was "Watneys Red Barrel" in 1931.