Hops made their entry somewhere around the 9th century and were gradually adopted. Brewers had previously used gruet - a mix of herbs - to flavor the beer. This didn’t have the preserving properties of hops so any beer made couldn’t have been exported. The medieval towns of Bohemia perfected hopped beer by the 13th century.
The industrial revolution brought about the industrialization of beer. A few other innovations in brewing came about with the invention of the thermometer and hydrometer in the late 1700s. The hydrometer, in particular, transformed how beer was brewed. It allowed brewers to calculate the yields from malt and led them to discover that pale malt had the highest yield. Brewers began using mostly pale malt and supplemented with high quality highly colored malt for color. The next innovation of the time, the drum roaster invented in 1817, allowed for the creation of dark, roasted malts, contribution to the flavors of porters and stouts. Finally, Louis Pasteur’s discovery of yeasts role in fermentation in 1857, led to brewers developing ways to prevent beer from souring.