It is like Christmas in August, or at least Octoberfest. As beer drinkers are turning into the gut of their annual calendar–Octoberfest celebrations kick off this week around the world–beer makers have been readying for months. As the chart above shows, seasonal beers have a calendar all their own, with special brews often released months ahead of their intended seasons. Samuel Adams’s Octoberfest, for instance, arrives on the shelves on August 1 when thoughts of fall couldn’t be more out of mind.

Brewers like the Boston-based company eye industry reports and inventories of retailers, who can sell only so many bottles despite the rising number of beer brands. This fight for shelf space is forcing fall beers to arrive during the summer, according to Danelle Kosmal, vice president of alcoholic beverages at research firm Nielsen. “This is something that’s just started in the past couple of years,” Kosmal says. “The calendar moves up a few weeks, earlier and earlier.”

And once we hit winter, beer makers will already be turning ahead to warmer days. After Jan. 1, sales of winter seasonals drop “like clockwork,” according to Al Marzi, chief of brewing operations at Harpoon Brewery. “Seasonals are like that,” Marzi says. “People are always anticipating the next one.”

Here’s a look inside the changes in beer’s annual calendar.

Fall

Weeks before the Northern Hemisphere Harvest beer hits shelves on Oct. 15, Sierra Nevada co-founder Ken Grossman and his veteran brewers gathered around a table in Yakima Valley, Wash. They unwrapped one-pound brewer’s cuts of hops, tearing off chunks of flowers, warming and releasing the aromas of the hops’ oils and resins. They sniffed for right smell: citrusy, but not bitter, piney, but not woody, earthy, but not musty.

Late summer and early fall mark the Gold Rush for hops, a flavoring ingredient in most beers, and Yakima Valley, where over three-fourths of America’s hops are produced, is home to the annual hop harvest. “It’s a one shot deal,” Grossman says. The hops—Grossman decided on Cascade and Centennial hops—will be freshly brewed into select fall beers, like the Northern Hemisphere Harvest. Others will be stockpiled for future seasons.

But these hoppy beers are normally the finishing touch of brewers’ fall lineups. By September, most fall beers have already hit shelves, even though it’s not technically fall. At Yuengling, Hallertau hops have already been imported from Bavaria, Germany, for their Oktoberfest beer, that debuted, like other American Oktoberfest beers, in August. (Oktoberfest traditionally starts in late September.) At Rogue Ales, over 1,000 lbs of pumpkins have already been hand roasted and brewed over six days for the Pumpkin Patch Ale, just one of many pumpkin beers that arrived months before Thanksgiving, and also go off shelves before Thanksgiving.

To get the freshest flavors of hops and pumpkins, it’s best to start in early August when fall seasonals start appearing on shelves. The earlier you’re able to stock up, the better. Because by Thanksgiving, many fall beers will be sold out or taken off shelves, and winter beers will have already started to roll out. Here’s three fall beers to look out for:

• Harpoon Brewery, Grateful Harvest: Made with cranberries, and $1 is donated to local food banks for each 6-pack sold

• Goose Island, Bourbon Country Brand Stout – Vanilla Rye: Made by manually inserting vanilla beans from Madagascar and Mexico into rye whiskey barrels

• Brooklyn Brewery, Brooklyn Post Road Pumpkin Ale: Made with hundreds of pounds of pumpkins blended into a mash

Winter

By November, things slow down. The craze of the hop harvest has ended. Most fall beers are off shelves. Some brewers make slight adjustments to the four main ingredients—grain, water, hops, yeast—of their existing winter beer recipes. Some don’t brew winter beers at all. Some, like Aaron Inkrott, lead brewer at Saint Arnold Brewing Company in Houston, Texas, fall into the rhythm of brewing set-in-stone recipes.

For Inkrott, the key to Saint Arnold’s winter brews is their proprietary yeast (“There’s no other brewery in the world that uses our yeast,” Inkrott says). While Saint Arnold isn’t the only brewery with its own yeast, the Texas brewery’s yeast strain creates a distinctly rich fruitiness, Inkrott says. The strain, used in Saint Arnold’s Christmas Ale, originated in a now-defunct British brewery, and was shared with Saint Arnold over 20 years ago.

Yeast, not real fruit, is responsible for the characteristics of most winter beers: dark, sweet, malty. In Saint Arnold’s Christmas Ale, for example, the yeast produces esters of strawberry, raspberry, raisin and black cherry essences, while other proprietary yeasts, like Rogue Ales’, finish off with a lighter, honey-like taste.

When the holiday fever of Christmas arrives, sales of these winter-flavored beers spike, according to Nielsen data. Yet the drop is just as rapid, too. Though most winter seasonals debut when fall seasonals go off shelves—in early November, well before Thanksgiving and the Dec. 21 winter solstice—they’re almost always out of fashion within two months.

Winter seasonals—there’s only a limited supply, like all seasonals—are likely to be depleted the week of Christmas. Chocolate malt and fruity yeast flavors will have deteriorated slightly, too, Inkott says. Here’s a few that just may be out of stock:

• Yuengling, Bock: Based on the old tradition in late winter of brewing a Bock, a dark brown brew

• Rogue Ales, Santa’s Private Reserve: A double hopped red ale with a roasted, malty flavor

• Shock Top, Twisted Pretzel Wheat: An unfiltered wheat ale with the taste of bakery-fresh pretzels

Spring

Only in the brewing world does spring start on New Year’s Day. Spring arrives when drinkers are bored of winter, a sort of seasonal depressive disorder that drips into the alcohol business. In fact, several spring beers cater to this mentality, including Harpoon Brewery’s Long Thaw and Samuel Adams’ Cold Snap, two citrusy, crisp Belgian-style white ales that tease springtime.

Belgian ales are the big trend in spring beer, and it’s Belgium’s beer culture that brewed up the idea of Blue Moon’s forthcoming First Peach Ale, according to Keith Villa, founder of Blue Moon, the craft brewer owned by MillerCoors. “The inspiration came from Belgium and the fruit beers they have over there,” Villa says. “Why not marry up those two styles and come up with a Belgian ale that has peach in it?”

Villa, who has a PhD in brewing science from the University of Brussels, Belgium, will organize a peach harvest in the Pacific Northwest. He’ll then work with a microbiologist to determine that there’s no wild yeast or bacteria on the peach skin that could spoil the beer, before chemically analyzing the flesh for the right sugar content, flavor and smell. Finally, he’ll coordinate the exact timing of cooking the malts, hops and peaches. “When I write a recipe, it’s like someone writing a symphony for the orchestra,” Villa says. “You have to take care of every little piece so the final work comes out just right.”

In reality, the First Peach Ale and other new spring beers are designed extra carefully in an attempt to fight the industry-wide slump during spring, when seasonal beer sales are at their lowest, according to Nielsen data. “Spring is typically a slow period, with trying to come up with something that sparks people’s interests,” says Scott Shirley, head brewer at Harpoon Brewery. Here are a few that just might spark yours:

• Sierra Nevada, Bigfoot Barleywine Style Ale: A rich, bittersweet body with the intensity of a wine

• New Belgium Brewing, Spring Blonde: A golden ale with aromas of lemon peel, pepper and fresh bread

• Saint Arnold Brewing, Spring Bock: An authentic, German-style Bock to celebrate the coming of spring

Summer

It’s summer, and you can relax. This is the longest season of seasonal beer. Summer beers start appearing in mid-March—when it’s actually still winter (The spring equinox is March 20). They last well into the summer, which starts June 21, going off shelves in late August.

Similar to brewing winter beers, yeast is of utmost importance for summer beers, according to Jennifer Yuengling, a sixth-generation Yuengling and plant coordinator at D. G. Yuengling & Son. The flavor in Yuengling’s Summer Wheat derives not only from brewing with wheat instead of 100% malt, but also from a particular yeast that produces banana and clover-like esters. There are hundreds if not thousands of yeast strains for brewing, Yuengling says, and a thorough analysis of their phenols, esters and alcohols is necessary.

These summertime flavors are such a hit that your favorites just might be wiped off shelves, particularly after holidays. Sales of summer seasonals spike on Memorial Day and Fourth of July, according to Nielsen data. Though sales drop immediately after, they’re still roughly twice the sales volume of winter and spring. “Sometimes what happens with the summer seasonals is the stores are running out, and they need to bring something in behind that shelf placement,” Shirley says.

And those replacement beers—fall beers—will be waiting to complete the seasonal beer cycle. By then, Yuengling will have imported hops from Germany, Rogue Ales will have harvested hundreds of ripe pumpkins, and Sierra Nevada along and brewers will have descended on Yakima Valley for the annual hop harvest. But before all of that happens again, as it will each year, here are a few summer beers to soak up:

• Blue Moon, Summer Honey Wheat: Wheat ale with clover honey and orange peel

• Saint Arnold Brewing, Summer Pils: A bohemian-style pilsner that’s crisp and malty, brewed with Czech hops

• Harpoon Brewery, Big Squeeze: A grapefruit shandy with real grapefruit juice