By Unseen Brewing Co. | New Beers | Read: ~5 min
Kettle sour is one of the most radical styles in modern craft beer: controlled acidity, built in a few hours where lambics take years, with a clean, precise, and deliberate result. Arakiri is our version — 5.5%, raspberry, brewed at CoHop in Brussels. A name that doesn't promise sweetness.
What is a Kettle Sour?
Kettle sour is a brewing technique born in the American craft scene of the 2010s, popularized precisely because it allows for clean and reproducible lactic acidity without the years of maturation required by traditional sour beers. The process is short, controlled, and surgical.
The technique gives the style its visual characteristics: depending on the brewer, the beer can be hazy (suspended yeast, wheat grain bill) or relatively clear. What doesn't change: acidity in the foreground, a clean and refreshing finish, almost total absence of bitterness. Hops play a minimal role — just enough for preservation.
On the palate, a well-executed kettle sour tastes like what a squeezed lemon would do if it were also a beer: the acidity awakens the taste buds, it doesn't assault them. Fruit, when added, doesn't mask the acidity — it complements it.
Kettle Sour vs Lambic: same acidity, opposite philosophies
In Belgium, lambics are born: sour beers spontaneously fermented in the Senne valley for centuries, aged in oak barrels, unpredictable and unique with each brew. Gueuze, Kriek, Faro — icons of Belgian brewing heritage. Their acidity is complex, wild, sometimes vinous or bretty. They take 1 to 3 years.
The kettle sour doesn't claim to replace the lambic. It's another answer to the same question — how to create acidity in a beer? The kettle sour answer: inoculate Lactobacillus into the wort at 43–46 °C, let it work for 24 to 48 hours under a protected atmosphere, then boil to kill the bacteria before classic fermentation. Result: clean acidity, no Brett, no wild character. Two sour beers, two ways of thinking about acidity.
The ingredients of Arakiri: barley, wheat, raspberry
Arakiri's grain bill is intentionally simple: barley and wheat. No oats here — this is not a beer for smoothness or creamy mouthfeel, it's a beer for acidity and liveliness. Wheat brings lightness of texture and a nice head; barley, the structure. The whole remains deliberately in the background to let the star make its entrance.
The raspberry is the argument. Added at the end of fermentation, it brings its citric and malic acid to reinforce the lactic acid already present — the acidity layers and complexifies. But most importantly, the raspberry projects the aromatic profile in a precise direction: fresh red fruits, a slight floral note, a clean finish. This is not a raspberry to sweeten the beer. It is a raspberry to transfigure it.
Hops, meanwhile, work behind the scenes. In a kettle sour, hop additions are minimal — just enough alpha acids to protect the beer, never enough for bitterness to settle in and compete with the acidity. The result in the glass: the entire foreground is occupied by raspberry and Lactobacillus.
Lactic fermentation: from wort to glass, step by step
It all starts with the usual brewing process: mashing, wort filtration, beginning of cooling. But where a classic beer would go directly to a boil, the kettle sour takes a break. The wort is cooled to 43–46 °C — the optimal temperature range for Lactobacillus bacteria — and inoculated with a pure culture of these bacteria.
The tank is then covered and protected from oxidation for 24 to 48 hours. The Lactobacillus works anaerobically: it consumes fermentable sugars and produces lactic acid. The pH drops from 5.5 to about 3.2–3.5. Then the acidified wort is boiled — the heat kills all bacteria, sterilizes the wort, and fixes the acidity. The yeast then takes over for classic alcoholic fermentation.
It is this two-step process — bacterial acidification followed by yeast fermentation — that gives the kettle sour its characteristic profile: a clean lactic acidity, without the wild or vinous notes that a Brett fermentation would bring. In Arakiri, the raspberry is added after fermentation, in the maturation tank, to preserve its most volatile aromas.
Arakiri: Kettle Sour by Unseen
The name evokes Japanese harakiri — a radical, precise act, with no turning back. Arakiri's acidity doesn't hesitate: it cuts. But like any precise gesture, it's not without reason. Every parameter was chosen — the acidification time, the Lactobacillus temperature, the amount of raspberry, the ABV.
5.5%: a deliberate choice. Low enough for the acidity and raspberry to dominate without alcohol burning the acidity on the palate. High enough for the beer to be structured, to deliver its aromatic promise without seeming diluted. The wheat-barley grain bill without oats confirms this direction: we're not looking for roundness, we're looking for sharpness.
On the nose: fresh raspberry, a slight floral note, and acidity already peeking through before the first sip. On the palate: a frank and clean tangy attack, the raspberry immediately takes over, light and lively body, a refreshing finish that makes you want to come back for more.
This is a beer for those who want uncompromising acidity — not a sweet raspberry to make the pill go down. Clean, fruity, sharp. That's Unseen.
Arakiri — Raspberry Kettle Sour 5.5% | Unseen Brewing Co.
FAQ
What's the difference between a Kettle Sour and a Lambic?
Both are sour beers, but the processes are radically different. A lambic spontaneously ferments in the open air for 1 to 3 years — complex, wild, unpredictable. A kettle sour acidifies the wort in a kettle in 24 to 48 hours using controlled Lactobacillus bacteria — resulting in a clean, reproducible product, without waiting. Two philosophies, not a hierarchy.
Why raspberry in Arakiri?
Raspberry naturally amplifies lactic acidity — its citric and malic acid adds to the lactic acid from fermentation. It also brings a fruity roundness that balances what Lactobacillus alone would make too austere. This isn't a raspberry to mask the acidity: it's a raspberry to project it into another dimension.
Is Arakiri very sour?
The acidity is frank and clean — that's intentional, it's Kettle Sour. But it's clean, without vinegary harshness, and the raspberry balances the attack. If you've ever enjoyed plain yogurt, a glass of unsweetened lemonade, or a craft raspberry lemonade, you have the palate profile for Arakiri. It surprises with the first sip, it convinces with the second.
Where to buy Arakiri?
Arakiri is available on www.unseenbc.com and at our partner bars and bottle shops in Belgium. Follow #unseenbc on social media for updated points of sale and new availabilities.