Priming with Kräusen
When it comes to brewing, there are several ways to achieve carbonation. Some brewers force carbonate, some add priming sugars, some add fresh wort (a.k.a. gyle) and some add young fermenting wort — also known as kräusen. Priming with kräusen is an effective way to bottle condition that not only produces carbonation, but also has some flavor advantages. Take it from two professionals who use this technique regularly.
Nik Stanciu is the Head Brewer and co-owner of Tuckerman Brewing Com-pany in Conway, New Hampshire. All Tuckerman brands are bottle conditioned and many use kräusen.
Firstly, priming with kräusen is a method of natural carbonation. Secondly, it works extremely well. Most large breweries including craft/micro breweries "naturally" carbonate their beer to perhaps 90% of their final target carbonation. The last 10% is performed by forcing CO2 into the final product via carbonation stones, etc. The advantage of this forced method is that the brewers should, in theory, get exact carbonation results. In practice, though, we have observed substantial carbonation variation from different breweries, even some very large breweries, that use this method.
Bottle conditioning, where the beer is primed with kräusen in the final package, i.e. bottle or keg, is less exact by nature. In fact, we have observed that in 8–10 days 95% of the fermentable sugars in the final beer will ferment out — however, over the next 60 days, the carbonation tends to creep upwards. This is predictable enough for us that we can actually tell how old our beer is by measuring the carbonation. Priming with kräusen in the final package has two very distinct advantages. First, bottle conditioning adds flavors to the final product that you just cannot get any other way. Second, adding kräusen to the final package is literally a “conditioning” process. When yeast digests wort to make beer, several intermediate metabolites are produced besides ethanol and CO2.
Two prominent, generally considered unwanted, metabolites are acetaldehyde and diacetyl. To remove these un-wanted flavors some brewers tend to age, condition, lager or secondary-ferment their beer.
This is why we call priming with kräusen a conditioning process. The idea is that kräusen contains very healthy and active yeast, which when added to well attenuated beer helps to push the intermediate metabolites to their final state, which is ethanol.
Breweries that produce lager often “lager” or age their beer in horizontal style tanks. Fresh kräusen is often added to help condition the beer, specifically to help remove diacetyl, which lager yeast tends to produce more of than ale yeasts. There is no reason not to use the same method with ales, though.
As far as flavors, if you taste fresh wort versus finished beer, wort has much stronger hop flavors both bitter and aromatic. During fermentation, iso-alpha acids from hops tend to adhere to the cell walls of yeast and thus as the biomass of yeast increases during fermentation, the overall bitterness of the wort-beer decreases. Aromatic components from the hops, are scrubbed from the fermenter by the evolution of CO2. By adding fresh fermenting hopped wort to the final beer and then packaging it, these more intense hop flavors are captured in the finished product.
The method of bottle conditioning complicates the entire brewery process, because you need to have fresh fermenting wort when bottling, and you can’t have fresh fermenting wort from a stout to use in conjunction with packaging a pale ale. For homebrewers, I would suggest hydrating, hopping and boiling some dried malt extract. Then, while it is still hot, pour it into clean 12-oz. (355-mL) bottles leaving no headspace, then cap it.
At this point, you should be able to refrigerate the bottles. Then, when you want to bottle condition a batch, open a bottle (room temperature), add some yeast, add an air lock and let the yeast get going. When it looks like it is fermenting well, add it to your finished
beer and package it. It will obviously take some trial and error to figure out how much to add and how far to let the wort ferment.
We let the sugar in the wort drop about 20–25% of its full attenuation before bottle conditioning and add around 5% by volume to the finished filtered beer. Most homebrewers don’t filter, so you might get away with adding the hopped wort from the 12-oz bottles directly to your finished beer, since it already has yeast in it. This should work, although you might have to wait longer before the beer is fully bottle conditioned, since the yeast is not at high kräusen.
Alan Sprints is the Head Brewer and owner of Hair of the Dog Brewery in Portland, Oregon.
I first discovered Belgian and British Ales that were primed with kräusen. These beers matured as they aged and got better as the years went by. Today in America, craft brewers are using bottle conditioning to help create unique beers, that will also improve with age. I think that sugar works fine until the beer gets above 7% ABV. Above that point, the yeast left over from fermentation will have a hard time refermenting in the bottle. This is when kräusening, or using newly fermenting wort, will benefit your beer. It will also produce a thicker, richer foam.
In the book “Vienna, Märzen, Octoberfest,” by Dr. George Fix (Brewers Publications, 1991), you will find a great formula to figure the amount of fermenting beer to add. The formula reads:
In this formula, the following factors are represented as follows:
• VP = volume of priming solution to be added
• VB = volume of beer to be primed
• SGB = specific gravity of beer to be primed
• SGP = specific gravity of priming solution
• F = fractional fermentability of priming solution
• CV = C02 level in volumes
So, as you will see, you need to use your hydrometer to measure both your youngly fermenting beer (“priming solution” in the formula above) and the beer to be primed. You will need to know how fermentable your young fermenting beer is (again “priming solution”) — e.g. 60% fermentable or 0.60 as a fractional. And finally, you’ll need to know the C02 volume you are shooting for in your final beer (typically between 2 and 3 volumes).
I brew two days before I bottle, and use that fermenting beer (a.k.a. kräusen) to prime when I start bottling. Using the formula in George’s book, I add the right amount of priming beer into my finished beer then bottle as usual. Although this process is involved, I think the results are worth it, especially for strong beers, ales and lagers.
Garrett Heaney is Associate Editor of Brew Your Own magazine.