Krausening (sometimes spelled kräusening) is a traditional German brewing technique where a small portion of actively fermenting beer is added to finished beer to naturally carbonate it. Instead of adding sugar or force-carbonating with a CO2 tank, the brewer uses fresh, vigorously fermenting wort as the carbonation source. The active yeast and residual sugars in that addition restart fermentation inside a sealed vessel, and the carbon dioxide produced dissolves into the beer.
How the Process Works
The basic idea is straightforward. A brewer makes a batch of beer and lets it ferment to completion. Separately, they brew a smaller batch of wort (unfermented beer) and let it begin fermenting until it reaches its most active phase, called “high krausen.” This is the point where the yeast is at peak activity, usually one to three days into fermentation, with a thick, foamy head on top of the liquid.
That actively fermenting wort is then blended into the finished beer. The vessel is sealed, or “bunged,” so no gas can escape. As the fresh yeast chews through the remaining sugars, the CO2 it produces has nowhere to go but into the beer itself, creating natural carbonation. The result is a fully carbonated beer without any added sugar, corn sugar, or external CO2.
Why German Brewers Relied on It
Krausening owes much of its history to the Reinheitsgebot, the German beer purity law. The original law stipulated that beer could only be made from barley, hops, and water. That meant German brewers couldn’t simply toss in table sugar or corn sugar at bottling to create carbonation, the way many homebrewers and craft breweries do today. They needed a carbonation method that used only ingredients already in the beer. Krausening fit perfectly: the addition is just more of the same wort the beer was already made from, carrying its own yeast and fermentable sugars.
This is why the technique became standard practice in traditional German lager production and remains common at German breweries today, particularly for styles like Pilsner, Helles, and Festbier.
How Much Wort to Add
The goal is to add just enough fermenting wort to raise the gravity of the finished beer by about three points on the specific gravity scale. That small bump provides enough sugar for the yeast to produce the right level of carbonation without over-pressurizing the vessel or leaving residual sweetness.
A common formula for homebrewers: divide 12 times the gallons of beer by the gravity points of the krausen wort. So for 5 gallons of finished beer using a krausen wort with a specific gravity of 1.060, the math works out to about one quart of wort. That single quart, teeming with active yeast and fermentable sugar, is enough to carbonate the entire batch.
The krausen wort doesn’t have to be from the same recipe as the finished beer, though matching the recipe keeps the flavor profile cleaner. Some brewers set aside a portion of their original wort before fermentation specifically for this purpose. That reserved portion is sometimes called “gyle.”
Krausening vs. Sugar Priming
The most common alternative to krausening is priming with sugar. Homebrewers typically dissolve corn sugar or table sugar into finished beer before bottling, and the residual yeast ferments that sugar to create carbonation. It’s simpler and requires no extra brewing. But krausening has a few advantages worth noting.
First, the fresh yeast introduced during krausening is far more vigorous than the tired, dormant yeast left at the bottom of a finished beer. This matters most for lagers and high-gravity beers where the existing yeast may have gone dormant after weeks of cold conditioning. The fresh yeast carbonates more reliably and can also help clean up off-flavors, particularly diacetyl, a buttery-tasting compound that some yeast strains produce during fermentation. A dose of active yeast at peak health is very effective at scrubbing diacetyl from the finished beer.
Second, because the addition is just wort, it introduces no flavors foreign to the beer. Sugar priming is essentially flavor-neutral too, but for brewers committed to an all-malt process, krausening keeps the ingredient list pure.
The downsides are practical. Krausening requires you to have actively fermenting wort ready at exactly the right moment, which means coordinating two batches or planning ahead to reserve wort. Sugar priming takes five minutes. For commercial German breweries running continuous production, timing is easy. For a homebrewer making one batch a month, it takes more effort.
Krausening vs. Force Carbonation
Most modern craft breweries skip natural carbonation entirely and use force carbonation, pumping CO2 directly into a sealed keg of cold beer. It’s fast, precise, and doesn’t require any additional fermentation. You can go from flat beer to perfectly carbonated in a day or two.
A side-by-side experiment by the brewing site Brülosophy compared force-carbonated Festbier to a krausened version. The practical takeaway: both methods produce well-carbonated beer, and the sensory differences are subtle enough that most drinkers won’t notice in a casual setting. The choice comes down to process preference and tradition more than dramatic flavor differences.
That said, many brewers who use krausening report a finer, softer carbonation compared to force carbonation. The theory is that CO2 produced slowly during natural fermentation integrates differently into the beer than gas forced in under pressure. Whether that difference is perceptible in a blind tasting is debatable, but it’s a real point of pride for traditional German brewers.
Using Krausening at Home
If you want to try krausening as a homebrewer, the simplest approach is to set aside a portion of your original wort on brew day, before pitching yeast. Store it sealed in the refrigerator. When your main batch finishes fermenting and you’re ready to bottle or keg, warm that reserved wort to room temperature, pitch yeast into it, and let it ferment for a day or two until it hits high krausen. Then blend it into your finished beer at the ratio described above and seal everything up.
Alternatively, you can brew a small, separate batch of wort timed so that it reaches high krausen on the same day you plan to package your main beer. This is more common in commercial settings where batches overlap on a regular schedule.
Bottled beer krausened this way typically takes two to three weeks to fully carbonate at room temperature, similar to sugar-primed bottles. The main practical difference is that krausened bottles may throw a slightly larger yeast sediment, since you’ve added a fresh, active yeast population along with the wort.