There are 2 basic categories of beer :
The difference between the 2 categories lies soley in the brewing processes involved.
These differences between ale and a lager comes down to 3 main differences in the brewing process.
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. That said 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).
2. Temperature and Time
Ale yeasts ferment best at warmer temperatures, usually around room temperature and up to about 24° C. For this reason, they tend to mature and ferment faster than lagers.
Lagers ferment at colder temperatures (8-10°C). Historically, lager beers came from continental European countries like Germany, 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.
3. Additional Ingredients
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, brewers of ales seem to be more experimental than lager brewers and often add additional ingredients known as adjuncts to their brews. This can partially be attributed to the German 1516 beer purity law (Reinheitsgebot) which basically limits beer ingredients to malted grain, hops, yeast and water (preventing the use of adjuncts). 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. The problem is that the law is outdated and has stifled creativity in many European breweries that specialize in lagers and still follow this law.