Lagers are brewed with “bottom-fermenting” yeasts at much colder temperatures, 35-50F (2-10C) over longer periods of time. The trick with lager yeast is they can survive, metabolize, and reproduce at lower temperatures and can assimilate compounds which ale yeast cannot, fewer by-products are produced which drop out during fermentation, the result is a very clean, sparkling beer. Lagers are best served at slightly cooler temperatures 40-50F (5-10C).