comprises a broad class of beers brewed using the top-fermenting yeast Saccharomyces cerevisiae. See yeast.

The recent craft brewing revolution in the United States has taken the English word “ale” and started to give it a whole new meaning. At one time, ale referred to only a few different beers from England. Today, ale has come to include a continuously growing number of beers, some new and some older than England itself.

One common conception of the world of beer is that it is divided into two categories, namely ales and lagers. All beers fermented by “top-fermenting” yeasts, that is, yeasts that tend to do their work at the top of a fermenting vat of beer, are called ales. All beers fermented by “bottom-fermenting” yeasts are called lagers. Top-fermenting yeast (S. cerevisiae) likes to ferment quickly (2–7 days) and at higher temperatures 15°C–24°C (60°F–78°F), whereas bottom-fermenting yeast (S. pastorianus) ferments more slowly (5–10 days) and at lower temperatures, 7°C–13°C (45°F–55°F). The higher temperature fermentation of ales with S. cerevisiae yields beers with a more fruity, complex flavor profile, whereas the lower temperature fermentation of lagers with S. pastorianus yields beers with cleaner, more directly ingredient-driven flavor profiles. See lager, lagering.

The idea that beer can be split cleanly into the two groups, ale and lager, is perhaps emotionally satisfying. In real life, however, the menagerie of yeast strains that brewers use does not actually fit so neatly into these two categories. In fact, the behavior of many yeast strains is somewhere between that of true top- and bottom-fermenting yeasts, and their genetics are much more complicated than a simple split between two species. The wide use of unitanks to ferment ales shows this quite clearly, and any experienced ale brewer knows that many yeasts can be “trained,” by selection during cropping, to gravitate toward the top or bottom of their vessels. Another problem is that even the term “beer,” when used in its general sense, refers to any fermented beverage made from grain. This includes such outliers as the corn-based chicha of South America and the rice-based sake of Japan, neither of which is generally considered an ale, despite the fact that they are both fermented using top-fermenting yeasts. This confusion over the precise definition of ale is nothing new.

The first instances in Old English of the word “ale” (ealu) do not do a very good job of pinpointing an exact recipe for the beverage. It is sometimes referred to as being bitter, sometimes as sweet, sometimes as made with honey, and sometimes as brewed with spices. Whatever the case, the word “ale” was introduced to the English-speaking world by the Danes, who knew the beverage as öl.

It was not until the 16th century that hops began to gain popularity as a bittering agent for English brewers to add to their ales. The hop vine was well known in England prior to this point, and the English were familiar with brews made by foreigners using hops. These brews were known to the English as “beers” and differed from England’s ale, which was brewed at the time using only water, malt, and yeast. Prior to the 16th century the English took their ale so seriously that brewers who “adulterated” their ale with hops or other spices were subjected to fines. The use of hops and spices in the brewing of beer as opposed to ale, however, was accepted.

Eventually, not even fines were sufficient to keep English ale brewers from experimenting with the use of hops in their ales. They found that adding hops increased both the quality and the longevity of their ale, and gradually the use of hops in ale came to be accepted by English ale drinkers and government officials alike.

Even with this acceptance of the use of hops in ale brewing toward the end of the 16th century, the term “ale” only referred to a select few English brews (most notably pale ale and brown ale) well into the 20th century. Porter, for instance, was considered its own separate brew from both ale and beer until recently. It is for this reason that so many laws in the English-speaking world, many of them still in force, refer to malt beverages collectively as “ale, beer, and porter” specifically; ales differed from beers in that ales used less hops and differed from porters in that they were light in color. Any casual walk around London will reveal pub signs that proudly announce the availability of all three of these beverages.

In fact, the term “ale” only began to become synonymous with top-fermented beers generally as late as the 1980s. References to “German ale” prior to this date are few and far between, with references to “Belgian ale” being all but nonexistent. It was not until the 1980s resurgence of interest in international beer styles, marked by the advent of microbrewing in the United States, that the term “ale” began to be used, somewhat confusingly, to refer to most top-fermented beers.

It is noteworthy that there are also some legal definitions of ale that are both confusing and incorrect. For example, in the state of Texas, ale is legally defined as any malt beverage with an alcohol content of more than 4% alcohol by weight (ABW) and is mutually exclusive of beer, which is defined as any malt beverage with an ABW of less than 4%. This definition disregards any other aspects of the malt beverage, such as it being a high-alcohol lager or a low-alcohol ale. Many brewers have been amused (or annoyed) to find that their strong lagers suddenly need to call themselves ales upon reaching the Texas border.

Thus, the modern conception of ale is extremely young and in a state of flux. Today, the term “ale” refers to beers ranging from the strong, fruity, spicy ales of Belgium to the crisp, clean, hoppy pale ales of the United States. Although there are a few exceptions, ales can usually be recognized by their distinctive, fruity character achieved through warm fermentation using the top-fermenting yeast S. cerevisiae.