When bars start switching out their taps from Sam Adams Summer Ale to Octoberfest, you know it’s fall. Learn more about how such beer is brewed at the Samuel Adams Brewery in Jamaica Plain, which holds free tours ($2 suggested donation, proceeds benefit local charities) Monday through Saturday. Not a Sam fan? Harpoon Brewery on Northern Avenue offers weekend tours and weekday beer tastings. Tours are $5 and tastings are free.