The hydrometer is an instrument used to measure the density of a liquid, which describes the amount of sugar in solution. With the thermometer, the brewers were able to analyse for the first time how different processes affected sugar yield and fermentability. They discovered yield from the mash was greatest between 145degF and 160degF degrees and in lighter roasted malts. Additionally, they were able to measure that beer mashed at 160degF degrees will ferment less than one mashed at 140degF, leaving a sweeter and less alcoholic beer.
The microscope allowed Louis Pasteur to discover yeast are responsible for turning the sugary wort into an inebriating beer. The first yeast strain to be isolated was saccromyces carlsbergensis, the lager yeast used by the Carlsberg brewery in Denmark. With the discovery of the microbial origins of fermentation, brewers developed sanitation methods to avoid unwanted infections. This allowed breweries to send their beers further distances.
Distribution became the focus after microbial control was established. In America, German immigrants raced to become the dominant brand in the nation. Even though bacteria was eliminated from packaged beer, spoilage would still occur due to chemical reactions. Cold temperatures reduced the reaction rate, which led Adolphus Bush to ship his beer in refrigerated rail-cars. After touring Europe, Bush modeled a pilsner after a local favorite in Budweis, Czech Republic. Budweiser would become the first national brand of beer by the end of the 19th century.
The Industrial Revolution changed the brewing industry more than any previous time period; the only other comparable event being the present Craft-Beer Renaissance. Styles that were perfected for thousands of years are being eschewed for hop-bominations and chocolate peanut butter porters (I'm still waiting for a durian fruit beer). Several new styles, particularly the pumpkin ale, will likely survive the test of time. However the bulk will follow Pepsi Blue into obscurity.