By Unseen Brewing Co. | New beers | Reading time: ~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 take — 5.5%, raspberry, brewed at CoHop in Brussels. A name that doesn't promise sweetness.
What is a Kettle Sour?
Kettle souring is a brewing technique born in the American craft scene of the 2010s. It caught on precisely because it delivers clean, repeatable lactic acidity without the years of ageing that traditional sour beers require. The process is short, controlled, surgical.
The technique also shapes the style's look: depending on the brewer, the beer can be hazy (yeast in suspension, wheat in the grain bill) or fairly clear. What doesn't change: acidity up front, a clean and refreshing finish, almost no bitterness at all. Hops play a minimal role — just enough for stability.
On the palate, a well-made kettle sour tastes like freshly squeezed lemon would if it were also a beer: the acidity wakes up your taste buds without attacking them. Fruit, when added, doesn't mask the acidity — it completes it.
Kettle Sour vs Lambic: same acidity, opposite philosophies
In Belgium, you grow up with lambics: sour beers spontaneously fermented in the Senne valley for centuries, aged in oak barrels, unpredictable and unique with every brew. Gueuze, Kriek, Faro — icons of Belgian brewing heritage. Their acidity is complex, wild, sometimes vinous or bretty. They take 1 to 3 years.
Kettle sour doesn't claim to replace lambic. It's another answer to the same question — how do you create acidity in a beer? The kettle sour answer: pitch 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 the regular fermentation. The result: clean acidity, no Brett, no wild character. Two sour beers, two ways of thinking about acidity.
Another process where time and temperature define the style: bottom fermentation, covered in our article on the Mexican Lager La Chingona.
The ingredients of Arakiri: barley, wheat, raspberry
Arakiri's grain bill is intentionally simple: barley and wheat. No oats here — this isn't a beer about silkiness or a creamy mouthfeel, it's a beer about acidity and liveliness. Wheat brings a light texture and a nice head; barley brings the backbone. The whole thing deliberately stays in the background so the star can make its entrance.
Raspberry is the point. Added at the end of fermentation, it brings citric and malic acids on top of the lactic acid already there — the acidity layers up and gains complexity. Above all, raspberry steers the aroma profile in a precise direction: fresh red fruit, a light floral note, a clean finish. This isn't raspberry to sweeten the beer. It's raspberry to transform it.
Hops 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 whole foreground belongs to the raspberry and the Lactobacillus.
Lactic fermentation: from wort to glass, step by step
It all starts with a regular brew day: mashing, lautering, starting to cool. But where a classic beer would go straight to the boil, the kettle sour takes a pause. The wort is cooled to 43–46 °C — the optimal temperature range for Lactobacillus bacteria — and inoculated with a pure culture of them.
The kettle is then covered and protected from any oxidation for 24 to 48 hours. Lactobacillus works anaerobically: it consumes fermentable sugars and produces lactic acid. The pH drops from 5.5 to around 3.2–3.5. Then the soured wort is boiled — the heat kills all the bacteria, sterilises the wort and locks in the acidity. Yeast then takes over for the regular alcoholic fermentation.
It's this two-step process — bacterial souring, then yeast fermentation — that gives kettle sour its signature profile: clean lactic acidity, without the wild or vinous notes a Brett fermentation would bring. In Arakiri, the raspberry goes in after fermentation, in the conditioning tank, to preserve its most volatile aromas.
Arakiri: Kettle Sour, the Unseen way
The name nods to the Japanese harakiri — a radical, precise act with no turning back. Arakiri's acidity doesn't hesitate: it cuts. But like any precise gesture, it isn't gratuitous. Every parameter was chosen — souring time, Lactobacillus temperature, amount of raspberry, ABV.
5.5%: a deliberate choice. Low enough for the acidity and raspberry to dominate without the alcohol burning on the palate. High enough for the beer to have structure and deliver on its aromatic promise without tasting thin. The wheat-and-barley grain bill with no oats confirms that direction: we're not after roundness, we're after precision.
On the nose: fresh raspberry, a light floral note, and acidity that shows up before the first sip. On the palate: a bright, clean tart attack, raspberry immediately taking up all the space, a light and lively body, a refreshing finish that keeps you coming back.
This is a beer for those who want acidity without compromise — not a sweet raspberry to sugar the pill. 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 ferments spontaneously in open air and ages for 1 to 3 years — complex, wild, unpredictable. A kettle sour sours the wort in the kettle in 24 to 48 hours using controlled Lactobacillus bacteria — a clean, repeatable result, no waiting. Two philosophies, not a hierarchy.
Why raspberry in Arakiri?
Raspberry naturally amplifies the lactic acidity — its citric and malic acids add to the lactic acid from fermentation. It also brings a fruity roundness that balances what Lactobacillus alone would make too austere. This isn't raspberry to mask the acidity: it's raspberry to take it to another dimension.
Is Arakiri very sour?
The acidity is bold and clean — that's intentional, that's Kettle Sour. But it's clean, with no vinegary edges, and the raspberry balances the attack. If you've ever enjoyed plain yoghurt or a lightly sweetened craft raspberry lemonade, you've got the palate for Arakiri. It surprises on the first sip and wins you over on the second.
Where can I buy Arakiri?
Arakiri is available at www.unseenbc.com and from our partner bars and beer shops in Belgium. Follow #unseenbc on social media for up-to-date stockists and new releases.