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Ales vs. Lagers
The difference between an ale and a lager comes down to 3 main differences in the brewing process which will be discussed below.
Ales are made with “top-fermenting” strains of yeast which means that the yeast ferments at the top of the fermentation tank. Actually, they typically rise to the top of the tank near the end of fermentation. Ale yeasts also tend to produce chemicals called esters that can affect the flavor of the beer, depending on which strain of yeast is used. Note that in rare cases, there are some brewers that use “bottom-fermenting” yeasts to make ales.
Lagers use “bottom-fermenting” yeasts which sink to the bottom of the tank and ferment there. Because they collect on the bottom of the tank, they can often be reused. The yeast in lagers does not usually add much in the way of flavor. This typically comes from the other ingredients in the brew (malt, hops, etc).
Keep in mind that there are exceptions to these yeast “rules”.
Temperature and Time
Ale yeasts ferment best at warmer temperatures, usually around room temperature and up to about 75° Farenheit. For this reason, they tend to mature and ferment faster than lagers.
Lagers ferment at colder temperatures (46-59°F). Historically, lager beers came from continental European countries like Germany, brewed where cooler temperatures are the norm. The word “lager” comes from the German word “lagern” which means “to store” which refers to the lagering process where the beer typically ferments over longer periods of time than ales. The combination of colder temperatures and bottom-fermenting yeast is responsible for the mild and crisp taste of most lagers.
Ale recipes often contain a higher amount of hops, malt and roasted malts, hence they typically have a more prominent malty taste and bitterness.
Furthermore, ales seem to have more room for experimentation than lagers, and often additional ingredients known as adjuncts are added to ales. In Germany, the 1516 beer purity law (Reinheitsgebot) limited beer ingredients to malted grain, hops, and water (preventing the use of adjuncts). Yeast was certainly in these old beers, but they were unaware of its existence at the time. The inception of the law was founded in a noble cause to prevent brewers from skimping on quality in order to save money by using cheaper ingredients. Many of the early American “pilsners” were inspired by German style lagers, however, as time went on, major American lager brewers began adding corn, rice and other adjuncts to their beers in order to save money.