How did refrigeration allow lager beer to be brewed during summer?

Historically, brewing lager was restricted to the winter months because the process requires bottom-fermenting yeast, which functions best at cooler temperatures. Before the advent of modern technology, brewers relied on ice harvested during the winter to keep their beer cool during the warmer summer months, a practice that gave the beer its name—derived from the German word lagern, meaning "to store".123

The development of mechanical refrigeration and ice-making equipment in the late 19th century fundamentally changed this by allowing brewers to maintain the necessary low temperatures year-round. By introducing vapour-compression refrigeration to the industry, brewers were no longer dependent on seasonal ice, enabling the consistent production of lager beer throughout the summer.124