Sam Adams was a brewer. You knew that already. But did you ever wonder what the stuff he concocted actually tasted like?

Wonder no more. To celebrate Boston’s 375th anniversary, the historians at Boston Beer Company have cooked up a heady, autumn-ready ale that’s a tasty approximation of the beers downed by our Founding Fathers and the Puritans before them. Served on draft only in Boston, it’s like a birthday present for us all.

Pouring cloudy and deep-glowing amber, this unfiltered ale immediately imparts a richly sweet aroma, tinged with a pleasing, earthy acridity. The first pull reveals a smooth and viscous beer, almost chewy, that splits the difference between smoky and sweet, with burnished notes of caramel and brown sugar. Well-hidden, too, is a faint bite of dark rum. That’s no accident.

"In colonial days, a significant portion of fermentable materials came from blackstrap molasses," says Sam Adams founder Jim Koch. So while Boston 375 uses two-row Harrington, Munich, and caramel malts, about a third of the fermentable stuff comes from molasses — hence the rum flavor. The subtle smokiness comes from a fourth type of malt, which Koch smoked lightly to approximate what early American brewers would have used.

Boston 375 is Koch’s own invention, made with self-imposed limitations that mimic colonial brewing techniques. Indeed, it’s hearty ales like this one that were quaffed with gusto — from mugs made of pewter, earthenware, or pitch-sealed leather — in taverns like the still-extant Green Dragon. Samuel Adams himself brewed many barrels just like it.

"He wouldn’t have had refrigeration, but beyond that, he would have had everything else," says Koch. "Nothing in the brewing process would have been unfamiliar to Sam Adams." He raises his mug, breathes in the rich and smoky-sweet aroma, and takes another sip. "It’s like history in a glass."

Samuel Adams Boston 375 Colonial Ale is available at the Green Dragon, 11 Marshall Street, in Boston; Joshua Tree, 256 Elm Street, in Somerville; and Orleans, 65 Holland Street, in Somerville.