The house yeast is a key ingredient in Allagash White. Photo courtesy of Allagash Brewing Co.

Allagash White is widely regarded as one of the most important American beers ever made. Distracted by shiny new objects, I am often guilty of taking it for granted – until I have another one and marvel at how this wonderfully silky, flavorful, complex Belgian-style wheat beer is available basically everywhere I go.

A list of its ingredients makes it seem like an elaborate puzzle: four types of malted barley, wheat, oats, three types of hops (Nugget, Crystal and Czech Saaz), coriander and Curaçao orange peel. Oh, and the humble-sounding “house yeast.” One might be forgiven for glossing over that final piece of the puzzle, which sounds so mundane compared to its fellow ingredients.

And yet, that yeast is the keystone upon which this legendary beer depends, indispensable to its aromas, flavors and hazy appearance. “Yeast is what we as brewers worship,” brewmaster Jason Perkins told Esquire magazine. “It’s what makes beer.”

Let’s start with the process. Beer is made of water, grains, hops and yeast. Malted barley (and sometimes other grains) are added to hot water to make a sweet tea-like liquid. Hops are added to the boil, their bitterness adding balance (and some aromas) to the sweetness of the wort. The hopped wort is then cooled and sent to a fermentation vessel, where yeast is added. The yeast metabolizes the wort’s sugars, creating alcohol, carbon dioxide and other chemical compounds like esters and phenols – some of which contribute to a beer’s flavor and aroma. As the yeast runs out of sugars to eat, it clusters (in a process called flocculation) and either drifts to the bottom of the fermenter or rises to the liquid’s surface, becoming dormant. Or sometimes, for “low” flocculation strains, some yeast stays in suspension, creating a hazy appearance – as is the case with Allagash White.

There are two main families of yeast used in brewing: ale yeast (Saccharomyces cerevisiae) and lager yeast (Saccharomyces pastorianus). (“Saccharomyces” means “sugar fungus” in Latin.) Lager yeast was first used in brewing roughly 200 years ago, by Bavarian brewers. Beers using lager yeast ferment at 40 to 45 degrees Fahrenheit and are conditioned at near freezing temperatures, resulting in relatively clean flavors without the spicy or fruity aromatics typical of ales. Ale yeast has been used in brewing for far longer, and thus there are far more genetic variations within these strains. Ales are normally fermented at well over 55 degrees Fahrenheit, and ale yeasts tend to generate a much greater range of aromatics and flavors than lagers. Yeast plays a role in developing the esters and phenols that can, for example, add clove flavors to a beer like Allagash White or spiciness and tropical fruit aromas to Allagash Saison.

But many beers call for a more muted yeast that works behind the scenes, ceding the stage to the aromas and flavors of the hops.

Maine Beer Co.’s Prince Percy Pilsner is made with a Bohemian lager yeast. Photo courtesy of Maine Beer Co.

The house yeast at Maine Beer Co. “imparts very clean, crisp flavors with low fruitiness and ester production,” according to quality director Dan Roberts. Because the brewery specializes in hop-forward beers, they wanted a “clean” yeast that essentially takes a back seat to the complex mixture of aromas and flavors featured in the hops. But depending on the beer, they will occasionally seek out a different yeast strain – sometimes experimenting with new combinations, sometimes relying on a yeast more traditional to a particular style. For Prince Percy Pilsner, Maine Beer chose a Bohemian lager yeast that produces a malty profile, some ester characteristics and a dry finish, while also allowing room for the expression of the hops.

One family of yeast strains that has become increasingly popular in the U.S. in recent years is kveik (pronounced “kuh-vike”). These strains have historically been used in Norwegian farmhouse brewing, preserved and reused over generations. Farmers didn’t brew all the time, so they couldn’t keep wet yeast alive from batch to batch. To get around this, they harvested and preserved yeast on things like wooden rings or logs – objects with plenty of surface area, looking something like vertebrae. During fermentation, the rings would be left in the wort, where they’d collect yeast; after fermentation, they would be hung up to dry until the next brew day, when they’d just drop the ring back in the wort. According to Lars Marius Garshol, an expert in the tradition, “kveik” has two meanings in Norwegian dialect: yeast and “to breathe new life into something.”

Jake Austin, head of brewery operations at Austin Street Brewery, says that the interesting history of kveik inspired the Portland brewery to use it in one of its own beers. While Austin Street’s house yeast – like Maine Beer Co.’s – ferments cleanly, the kveik strain they selected for Bombtrack, an 8.5% Double IPA, was much more evocative, with the yeast’s orange notes complimenting the stone fruit and citrus of the Simcoe hops. The brewery plans to experiment further with kveik strains in the future.

Kveik has another local advocate in Simon Burhoe, head brewer at Mast Landing Brewing Co. In an interview with Hop Culture, Burhoe linked the current interest in kveik to the popularity of juicy IPAs, noting, “some kveik yeasts can be insanely tropical (and) fruity which really works in New England IPAs and compliments all the fruit-forward hops brewers are using.”

Of course, Maine brewers using kveik strains aren’t dropping wooden rings that have been cultivated within their families for generations into their wort; commercial brewers can get yeast from labs like White Labs, Wyeast, and Maine’s own Mainiacal Yeast Labs (which specializes in kveik strains). But another brewing technique featuring yeast more closely resembles traditional practices.

In 2007, Allagash built the first commercial coolship (or “koelschip”) – a shallow, open vessel historically used in Belgium to cool the wort overnight, while also exposing it to ambient yeasts and other microflora (a process called “spontaneous fermentation”). The following day, the wort – now inoculated by wild yeast – is sent to a fermentation tank, before ultimately making its way to oak barrels. Because the yeast is hyperlocal – at Allagash, it floats in through the windows or drops from the untreated wood beams of the ceiling of its coolship room – it is unique (and funky). Today, most “wild” beers use lab-controlled Brettanomyces yeast, which can add fruity and floral aspects to the beer as well – modern expressions of this older, “wilder” pre-modern technique.

There is a brewing adage: “Brewers make wort, yeast makes beer.” Indeed, without yeast, we’d all just be drinking grainy tea (or, more likely, drinking something else).

Ben Lisle is an assistant professor of American Studies at Colby College. He lives among the breweries in Portland’s East Bayside, where he writes about cultural history, urban geography, and craft beer culture. Reach him on Twitter at @bdlisle.


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