This category of beer uses yeast that ferments at the "top" of the fermentation vessel, and typically at higher temperatures than lager yeast (60°-75°F), which, as a result, makes for a quicker fermentation period (7-8 days, or even less). Ale yeast are known to produce by-products called esters, which are "flowery" and "fruity" aromas ranging, but not limited to apple, pear, pineapple, grass, hay, plum, and prune.