PORTLAND, Ore. ( TheStreet) -- We got our first pumpkin beer press release Aug. 3 from New Belgium Brewing in Fort Collins, Colo.Just after that, we got reports Shipyard Brewing in Portland, Maine, had been putting its pumpkin ales on shelves since late July. The person issuing the report was ecstatic. By now, it should be an accepted fact that just as supermarkets will begin stocking Halloween candy in their seasonal aisles after Labor Day and department stores will begin hauling out their first Christmas items in mid-September, pumpkin ales will be an end-of-summer staple. It's still a bit jarring and raises the question of who'd want said beer during the summer, but the brewing calendar is becoming as normalized as the retail calendar for reasons driven by both business and human nature. The fundamental truth behind it is that beer brewers, especially small brewers, operate extremely close to the margins and don't like to have beer laying around when nobody wants it. Jim Koch, founder of Boston Beer ( SAM) and the Samuel Adams brand, notes that as much as fans love his Samuel Adams' Old Fezziwig holiday brew just before the holiday season, they want nothing to do with it once the clock strikes midnight on New Year's Eve. It works the same in just about every season. Summer ales start cropping up in March and are off the shelves by July. Seasonal porters and stouts are a tough find after St. Patrick's Day. Brewers are starting to realize that their drinkers have a very specific window for these beers, and fatigue shuts that window abruptly when July vacations yield to back-to-school planning and Thanksgiving leftovers are cleared out before the winter holidays. The other motive behind getting the jump on pumpkin brews stems from the fact that they're not exactly a novelty anymore -- all the bigger brewers are picking their own pumpkins. For instance, Samuel Adams now brews its own Pumpkin Ale and toyed with a pumpkin stout before releasing its 8.5% alcohol by volume Fat Jack imperial pumpkin ale in 2011. Demand for pumpkin ale has grown so much within the past decade that Anheuser-Busch InBev ( BUD) introduced Michelob Jack's Pumpkin Spice Ale in 2005 and MolsonCoors ( TAP) countered with with Harvest Moon ale in 2006 before rebranding it as Harvest Pumpkin Ale last year, when it was on shelves by July.