From Kettle To Barrel: How To Brew a Fruited Sour Beer

It’s pretty safe to speculate that most of the post-Enlightenment Belgian farmers and publicans who discovered the delightfully mouth-puckering complexities they could achieve by adding cherries and raspberries to their spontaneously fermented ales probably never envisioned that their creations would evolve to the Raspberry Pineapple Lemon Coconut Ice Cream smoothie sours of today. But from the traditional – barrel-aged kriek/framboise lambics and German Berliner weisses mit schuss (with syrup) – comes the modern, and here we are brewing up a rainbow of fruited sour styles as fast as consumers can quaff them. 

“Fruit beers are fun,” writes Randy Mosher in Craft Beer and Brewing magazine. “They’re also among the most complex and challenging beers out there.”

The challenge for a brewer begins when choosing a style and a fruit flavor and ends at the assurance that no dangerously volatile cans or bottles have made it to market. Between these steps, a brewer has to address dozens of issues that don’t arise in a simpler brew schedule, including what form of fruit to buy and when to add it to the beer.

The What and When of Fruited Sour Styles

“There are really two types of sours: kettle sours or wood-aged sours, and they’re very very different animals,” says Fal Allen, brewmaster at Anderson Valley Brewing and author of Gose: Brewing a Classic German Beer for the Modern Era.

Most modern goses, Berliners, sour IPAs, and Catharina sours get acidified in the kettle with the addition of lactobacillus, while contemporary wood-aged or “wild” styles typically derive their characteristic tartness and/or funk from lactobacillus, pediococcus or Brettanomyces added during or after primary fermentation, plus maybe some time spent aging in a barrel.

“Kettle soured beers are bright, sharp beers with clean acidity, and sour beers made the other way are certainly complex, often involving multiple types of yeast, bacteria and wood flavors,” explains Allen.

Kettle Souring

Though one can add fruit on the hot side of a kettle sour – advantageous in that it kills off unwanted microflora though disadvantageous in its habit of unintendedly extracting fruit pectins, colors and certain flavors – Allen prefers to add it to the fermenter, at or near terminal gravity.

“We get a lot of good fruit flavor and you don’t have to worry about it refermenting in the package,” he says. “If you put it in earlier, during active fermentation, the process of CO2 creation will probably blow off a lot of the aroma and some flavor.”

Because any amount of fermentation will suck up some sweetness, brewers designing a sugary-tasting beer often opt to adjust the mashing or the malt process or – if they take a lot of precautions – backsweetening before packaging.

As a pioneer of the sour slushy beer, including the above mentioned Raspberry Pineapple Lemon Coconut Ice Cream J.R.E.A.M. Hydra, Burley Oak Brewing adds fruit to its kettle-soured wheated beers after fermenting and cold crashing – in the conical if brewers want the pulp to drop out and in the brite if they don’t.

COO Adam Davis warns fruiting in the brite can create too thick a substance for some sales accounts.

“We’ve gotten some kegs returned that there’s nothing wrong with,” he says. “They just didn’t understand it. Or If there’s a flow control on the faucet they can get clogged.”

Barrel Aging

When New Belgium Brewing’s wood cellar director and blender Lauren Limbach crafts one of her many fruited sours, she often first transfers the base beer – a dark or light lager, fermented and filtered in the main production stainless cellar – into an inoculated foeder. A few months before it reaches stable (sour) maturation, all but 10% of the foeder gets transferred to a purged and dissolved oxygen (DO)-ensured tank filled with processed whole fruit, puree or juice. She then adds pectinase to break down pectin-derived polysaccharide sugars before the liquid goes back into a vessel.

“What you’re doing is fermenting the fruit with the still active Brettanomyces/wild yeast and then holding it long enough to ensure it’s stable for package,” she says.

She circulates the pectinase between two and four hours (around 60 hl/hour) at room temperature and uses game bags to hold otherwise messy whole fruit in place. Then she checks to ensure very low levels of DO. Some fruits contain a lot of iron, which like any oxidizer interacts with wild cultures to create THP, a mousy or cereal-like off-flavor that can take up to 6-8 months to clear.

At this point the beer is ready to go back into wood. For a more fruity, sour profile, Limbach ages at room temperature only as long as the fruit fermentation and stabilization lasts. If looking to accentuate the barrel characteristics, she lowers the temperature and ages longer.

Selecting the Starring Ingredients

Do some fruits take better to sour styles than others? Sure. But there are myriad factors to consider beyond flavor. 

“I’ve broken up with plums,” announces Limbach. “The iron (and pectin) level is so high you’re gonna wait on THP (to clear). Saying that, we just recently made a 33% plum, 66% blueberry. Loved it. Glutton I suppose.”

“I’ve never made a gose with lime,” says Allen. “It would be a bit too much acid on acid.”

Allen also didn’t like how guava interacted with his lactobacillus and tropical-tasting yeast, and it turns out peach with apricot tastes more like peach than peach alone. 

This doesn’t mean brewers shouldn’t experiment with any and all fruits, it just means they must adjust their approach to account for idiosyncrasies. 

For instance, the riper the fruit the greater the sweetness; the greener the fruit the greater the acid. Harder fruits like apples and pears contain more pectin, which contributes to haze and turns to jelly when combined with sugar, heat and acid.

And, says BSG HandCraft North American sales manager Mike Brennan, “Tannins increase perception of bitterness so turn down IBUs if using tannic fruit.” 

At Ebb and Flow Fermentations in Cape Girardeau, Missouri, owner DeWayne Schaaf stays at the ready to dry hop when needed to raise the pH of his hybrids made with white-grape wine, which tend to drop in pH when fermenting. 

He says of his early malt piquettes, made by refermenting beer and the juice of grape skins, seeds and stems, “We were using chambourcin and the flavor on them was fantastic.”

Judging a Fruit by its Package

What form of fruit is best? Like so much in brewing, it depends on what you’re after.

Davis packs five-to-ten gallons of puree per barrel into his J.R.E.A.M. smoothie series and recommends asking vendors for samples to assess its pulpiness. (Side note, he finds the ice cream powder he usually uses dissolves best in the kettle with the hops after checking to make sure it doesn’t contain anything to inhibit fermentation. He adds his lactose then too.)

But Schaaf, who can lovingly describe the cinnamon character that can be coaxed from the stem of a grape, wholeheartedly advocates for whole fruit in fruit beers.

“If you use puree, you don’t get the ‘Oh, crap, that’s the tastiest, most complex beer I’ve ever had’ reaction,” he says.

However, purees, juices, extract and essences are far easier to use, and that’s not just because they don’t require processing at the brewery level.

Limbach cautions, “If you get a puree it will be supposedly clean but once you introduce whole fruit you are introducing a whole litany of mysteries and question marks,” like naturally occurring yeast, bacteria and insects.

If you do use full-size fruit, prep it by removing thick skins and large pits; puree in a food processor and consider freezing then thawing it twice to break down the cell walls and make the sugars more accessible. If you’re adding it on the cold side, Brennan suggests pasteurizing it in a double boiler for 15 minutes between 150-170 degrees, taking care not to activate the pectins by heating too long.

Preventing Juice Bombs and Fruit Gushers

All of this advice comes with a huge heaping of caution about post-fermentation fruit additions: while they may result in sweeter, fruitier beer, their sugars can cause the beer to referment and burst through glass, aluminum, and even wood. 

While some breweries warn consumers to keep the beer cold, it’s safest to pasteurize again before aging or packaging. Limbach takes readings of her post-primary gravity, ABV, and pH and won’t package until she safely circles back to that first gravity measurement if the goal is live beer bottle conditioning. 

“A full fermentation in the expected time frame and one final data point that ensures stability is the most important thing to achieve before package,” she says.