"Hops are what we like to call the spice of beer," says Robbie O'Cain, brewmaster at The Starr Hill Brewery in Central Virginia, one of more than 4,200 breweries in the United States.

O'Cain says hops are especially important to craft, micro and nano-breweries, which have opened in almost every state, specializing in beers with more flavor.

"The United States was once seen as this beer wasteland. All the other countries in the world who have rich brewing histories were like, 'Oh American beer. It's terrible. It tastes like water!' Now, they're drawing inspiration from us."

Starr Hill will use about 20,000 kilograms of hops this year to produce pale ales, lagers and stouts – adding aroma and a bitter taste.

"They're meant for balance, otherwise beer would be pretty sweet," O'Cain says.

Bitter news

But in 2015 some brewers got bitter news – a shortage of hops and higher prices.

Stan Driver is known as the Godfather of Hops in Virginia, where he cultivates the aromatic green blossoms for two breweries in the Blue Ridge Mountains

"Last year, Germany had an atrocious growing season," O'Cain recalls. "There was some really bad weather that led to really poor crop yields. Their entire yield was down about 25 to 30 percent, and we use those German hops in all of our lagers."

Fortunately, he says, Starr Hill had contracts locking in supplies and prices for several years. That's the norm for most brewers, but new or smaller ones scrambled to find enough of the hops they needed.

Hops are green cone-shaped flowers that grow from vines strung along poles and wires. From a distance, you might mistake them for grapes, and like grapes, they're very particular about where they'll grow.

Ann George heads the Hop Growers of America, an organization based in the Pacific Northwest, where 97 percent of US hops are grown. On summer nights, it's light until at least 10 o'clock.

Happy hops

"If you look at the major hop growing regions around the world, they're clustered around the 45th parallel," she says. "That is because of the photosensitivity of the hop plant. They will set a much heavier bloom for a much bigger yield the closer you are to the 45the parallel."

Hops can be used fresh – so called "wet hops" – but are more usually dried, and sometimes processed into pellets likes these

East of the Cascade Mountains in Washington, Oregon and Idaho, the air is dry, preventing mildew and other fungal diseases from destroying the plants. Water needed for irrigation usually flows freely from mountain streams to the Yakima and Willamette Valleys below.

American growers produced more hops last year than the world's long-time leader, Germany. But a prolonged drought in the American west worried farmers. Now they are planning more reservoirs and adopting new techniques to conserve water.

"Through the use of soil sensors, growers can very carefully monitor the amount of moisture being added to the plant and fine tune that application specifically to what the plant needs," George explains.

New varieties

And even in states where conditions are not ideal, growers are getting in on the game.

In Virginia Stan Driver grows hops for two breweries in the Blue Ridge Mountains. Scientists at nearby Virginia Tech are working to develop hybrid varieties that will grow better in this mid-Atlantic state, but for now Driver admits that yields of existing plants are low.

Hops need the just the right conditions to flourish, meaning climate change can have a major impact on harvests

And brewers are capitalizing on the availability of so-called wet hops, making a special ale with cones fresh from the field.

"Using the wet hops is comparable to using fresh herbs versus dried herbs, so when you put those wet hops in beer, you get a blast of aroma," Driver says. "We invite the public in to help us pick, and it's always fun."

One brewery in Richmond has even enlisted its customers to do the growing – giving them pieces of stem – known as rhizomes – and instructing them on how to cultivate the plant in their own gardens. Those who take part will find their names on the label of local pale ale produced with the hops they deliver.

Global trade

Hop cultivation is also taking hold in countries like China, Argentina, Australia and New Zealand, adding to the supply already coming from the US, Germany, England, Belgium, France and the Czech Republic.

Experts hope that geographic spread will protect the market from regional losses caused by climate change.

Brewers are learning to work with different varieties of hop and substitutes for another basic beer ingredient – barley – which could also be hit by droughts, storms and temperature extremes.

And small brewers are bracing for climate change by creating an online marketplace – the Lupulin Exchange – which acts as a broker, allowing brewers around the world to buy and sell hops.