By now you know that Göller Brewery uses only natural carbonation in their beer. How, then, do they lagger their beer in cold secondary fermentation tanks for up to 10 weeks without losing the CO2? The answer lies in a combination of technology plus a simple, ancient craft trick called "kräusening." First of all, the technology used involves a spunding valve. This German invention releases gas pressure above a set amount, allowing for the carbonation to build to the desired amount. But even with this technology, carbonation levels would sink too low over 10 weeks without kräusening. Kräusening (pronounced KROI-sen-ing) is adding a small volume of actively fermenting wort to beer that has just finished fermenting. In other words, it means restarting fermentation in a batch that already finished fermenting by adding a little extra wort from another batch. "Kräusen" itself refers to the yeasty foam at the top of a fermenting wort.
Göller performs the kräusening when they transfer the beer to secondary fermentation tanks. The primary fermentation has already done most of the work over a few days, but the secondary fermentation brings the beer to the superb level of perfection that Göller beers are known for. The extra wort added does a couple of good things to the beer. First of all, the natural bi-product of any primary fermentation is diacetyl (buttery off flavors) not desirable in a smooth lager. Luckily, these unwanted flavors get eaten up by the secondary fermentation and also dispersed by the long aging process. The other thing kräusening does is add more CO2 carbonation to the beer, giving it that rich and creamy fizz that can only come from natural carbonation. Adding sugar and yeast to condition the bottle/keg is not an option for a Reinheitsgebot brewery like Göller, so they add a little fresh wort. This ancient method of kräusening dates back to at least the 16th Century, when it was used mostly for beer barrels that needed to travel a little distance. The extra fermentation ensured a fresh beer on arrival.