Top-fermented beer: The yeast rises to the surface during the brewing process. Since the fermentation temperature is relatively high at 59 to 72°F, the yeast yields a beer that is high in esters and alcohol content. This often makes for a fruity aroma.
Bottom-fermented beer: The yeast sinks to the bottom after fermentation. During production, the beer requires a temperature of below 50°F. Consequently, this has only been possible since the invention of refrigerators.