Kräusening For Homebrewers

Kräusening is a lagering method with two main uses. And both are based on the same basic technique of adding some beer in the “high kräusen” stage of fermentation to beer that has undergone primary fermentation. The attenuation level of the beer being kräusened is what divides the two uses. Let’s start with beer that has undergone a normal and relatively rapid primary fermentation and finish this discussion with beer that is either lagging towards the end of the race or is predicted to soon begin to lag.

Some brewers use kräusening as a routine method of lagering where about 8.5 parts of fermented beer is moved into a lagering tank followed by the addition of about 1.5 parts kräusen beer. These two beers can be brewed from the same recipe or a special kräusen beer may be brewed specifically for kräusening. Breweries routinely kräusening face the challenge of having kräusen beer in the right stage of fermentation, the high kräusen or “high crown” stage, to add to the beer being kräusened. The solution to the challenge is proper planning so that actively fermenting beer with about 75% or more of its original wort gravity is available for kräusening. When a brewer kräusens several different beers, a standard kräusen beer makes sense in a production facility.

Scheduling details aside, what’s up with the method? Kräusen beer is added after the attenuated beer is added to the lagering tank because the kräusen beer is heavier than the other beer and will layer on the bottom of the lagering tank. This is especially relevant when a horizontal lager tank is used. The cool and handy part of this process is that the kräusen beer brings with it healthy and vibrant yeast, fermentable sugars, and wort nutrients. Think of this beer as a fresh crew on a construction site coming to relieve the tired folks who have been working for 10 hours and need to rest.

Because the kräusen beer is layered on the bottom of the tank, the release of carbon dioxide and the generation of heat sets up gas and convective currents in the lagering tank. In other words, the tank is mixed by the action of the fresh yeast on fermentables. Some breweries add surface area to the lagering tank in the form of beechwood chips and this surface area serves as a huge site for yeast to do cool stuff to the fermented beer in the tank. More on that in a second. While you have been reading and I have been typing, carbon dioxide has been sneaking out of the lagering tank, so let’s attach a spunding valve and carbonate our beer while this cool stuff is happening.

The cool stuff is an increase in maturation rate. Diacetyl and acetaldehyde are the two heavy hitters whose concentrations in beer usually dictate the time required for lagering. Many breweries monitor these two aroma-active molecules before deep chilling and filtration. Because active yeast accelerates the biochemical reduction of diacetyl into 2,3 butanediol and acetaldehyde into ethanol, aging times can be cut when yeast absorbs these “green” compounds from beer, biochemically reduces these by moving hydrogen from NADH to acetaldehyde and diacetyl, thereby regenerating NAD+. Although the concentrations of acetaldehyde and diacetyl are indeed lowered (reduced) by this reaction, the term “reduction” refers the movement of hydrogen in these biochemical reactions.

So in effect kräusening speeds up aging! And by the time the beer is fully attenuated by the clean-up crew, it’s also carbonated with hopefully none of the green aromas of young beer. We are talking brewing here, so things don’t always go as planned and the process must be monitored like anything else. The technique is called kräusening, not Prest-O Change-O.

Kräusening is also an extremely powerful arrow in the brewer’s quiver for warding off lagging, high-gravity fermentations or as an emergency tool to deal with the occasional lagging or stuck ferment. Many of us are surely thinking about brewing strong beers for the winter and are checking out the malty malts for doppelbocks. This is a great style to simply plan on kräusening. The benefits are the same as described above, but unlike kräusening a Pilsner or helles fermentation with kräusen beer that is brewed from the same recipe, strong beers, like doppelbock, do not make great kräusen beers because their strength is stressful on yeast. In a commercial brewery with several brews to choose from, a brewer may kräusen as a Plan B emergency and simply grab a bit of normal strength beer from a batch that will not stick out in the beer being jump-started. Drastic times sometimes call for drastic measures, but some lagging ferments should come as no surprise in certain styles. I suggest simply planning on kräusening for bigger beers like doppelbock, barleywines, imperial stouts, etc. Just because kräusening is a lagering method does mean that it cannot be used for ale.

So, let’s finish up with a brief how-to-kräusen summary. In this example, the beer being kräusened is a Mashinator Doppelbock. The minimum wort strength of this fictitious brew, as defined by the conventions of doppelbock naming, is 1.076 (18.5 °Plato) because the suffix “-ator” is used. We’ll revisit that in a moment. OK, here we go:

• The brew day will be normal, except we are going to get a bit clever with our wort strength and volumes. For starters, the target wort strength is going to be bumped to 1.082 (19.65 °Plato) because our beer will contain 85% of the total fermented from 1.082 (19.65 °Plato) wort and 15% of the total from a 1.048 (12 °Plato) wort, for a blended wort strength of 1.076 (18.5 °Plato). The total volume in this example is 6 gallons (23 L) of beer (full-strength wort + kräusen wort).
  We also will prep for kräusening by pulling 0.55 gallons (2 L) of 1.082 (19.65 °Plato) wort and diluting to 1.048 (12 °Plato) by adding about 0.35 gallon (1.3 L) of water, then freezing for future use as kräusen beer.
  At the end of the brew day, the goal is to start our fermentation with about 5 gallons (19 L) of 1.082 (19.65 °Plato) wort.
• For this example, the transfer trigger into lagering will be when our fermentation has dropped to about 1.028 (7 °Plato) because that’s about when fermentation rate can begin to lag. In other words, we want the relief crew to start working before the day shift packs it up for the evening! This is where some educated guesswork is required.
• When the fermentation is down to around 1.034–1.036 (8.5–9.0 °Plato), we are going to take our frozen wort from the freezer, thaw, boil to sterilize, cool, aerate, and pitch with fresh yeast. Whether liquid or dry, pitch based on the volume of kräusen beer. In this example, that’s 0.9 gallon (3.3 L). This mini-fermentation can be conducted in a glass jug or small bucket. After about 48–60 hours, the fermentation should be in the high kräusen stage and ready for use.
• Rack the high-gravity beer into a Corny keg, a handy 5-gallon (19-L) lagering vessel, through the dip tube (the keg’s “Out” connection), then rack the kräusen beer into the keg, again through the dip tube, connect a hose to an “In” fitting, and insert the end of the hose into a container of water. This allows for visual monitoring of the fermentation by observing gas bubbles and also allows time for carbon dioxide to freely escape the lagering tank and flush oxygen from the headspace. After 1–2 days of fermentation, replace the hose with a spunding valve adjusted to the correct pressure for the tank temperature. In this case, assume the lagering tank is at 50 °F (10 °C) and we want to equilibrate at 18 psig (gauge pressure) for about 2.5 volumes of gas. As fermentation builds pressure in the lagering tank, the spunding valve will begin to vent excess gas once the pressure reaches 18 psig.
• That’s it until fermentation is over. Taking samples is only required if you want to. If this beer is for holiday enjoyment, I would leave it at 50 °F (10 °C) for about three weeks, sample at the end of this period to confirm that the show is over, remove the spunding valve, then transfer the keg into a cold spot.

Response by Ashton Lewis.