Yeast & Fermentation

Cold weather alone doesn't make a lager a lager, yeast does. Boston Lager is fermented with bottom-fermenting yeast that works at low temperatures, usually around 8 to 13 °C. Afterward the beer is lagered cold for several weeks until it tastes clear and smooth.

Harpoon IPA, Trillium, and Tree House, on the other hand, brew with top fermentation. Top-fermenting yeast works at room temperature, typically around 18 to 22 °C, and lends the beer fruity aromas. Fermentation takes less time than with lager.

With hazy beers, yeast plays a second role. Brewers choose strains that deliver plenty of fruit character, think peach or pear, and leave a portion of the yeast in the beer. The hops that steep in the fermenter also form new aromas together with the yeast. The beer is not filtered.

Brewing takes place in stainless steel tanks with conical bottoms, where the yeast collects and can be drained off. The beer is then canned, often with as little oxygen exposure as possible. Oxygen ages hazy IPA quickly, darkening the color and giving the taste a cardboard-like note.

Boston Lager, while also sold in cans, can handle more aging. A canned hazy, by contrast, is meant to be drunk within a few weeks, according to the recommendation of many breweries. That's why some cans carry a packaging date, and many taprooms sell freshly brewed beer right on site before it has spent much time in transit.