Kraeusening

Besides corn sugar and DME, beer can also be carbonated with unfermented or actively fermenting wort. This procedure is usually used by breweries that bottle condition their beers. And the reason for this is simple: freshly fermenting wort is readily available in a brewery. It also has several advantaged over the priming corn sugar/DME:

• the flavor of your beer will not be changed, since you are adding part of the original wort (same IBUs, same malt profile, etc.)
• the apparent OG will not be changed. (if you use a highly concentrated sugar solution your FG and ABV will be as if the beer had a 2-3 GU higher OG)
• in the case of Kraeusening fresh and healthy yeast is added which does a better job in scrubbing the beer of O2 and off-flavors. In this case you can also use your bottles as a yeast bank since it is not the least flocculant yeast that is at the bottom of those bottles
• carbonation times will also be more predictable if you add fresh yeast
• you will have more beer to bottle and can get 5gal out of using a 5 gal carboy for fermentation.

The main disadvantage is the added complexity.

Preparation

If you want to prime with Speise (unfermented wort) or Kraeusen (fermenting wort), you want to keep some of the original wort from the brew day. Some brewers just keep it in a jar in the fridge, but I like to store mine in the freezer. This way I don't have to worry about something growing in there for the next 3 weeks that it takes until I bottle. I also don't worry about sanitation when I collect the Speise. As shown in the whirlpool article, I get most of it by filtering the hot-break/hop sludge, that is left in the kettle, through a paper towel.

Once I need it, I will take the Speise from the freezer defrost and boil it for 10 min in a 2000ml Erlenmeyer flask. This will sanitize it. If you need to add more bitterness to the beer, you can also add hops to this boil and boil longer. Chill the wort overnight or in an ice-bath.

If you want to bottle with Kraeusen, you need to inoculate it with yeast. Either add some fresh dry or liquid yeast. I simply take a sanitized racking cane to pull some yeast samples from the fermenter. Close one end of the cane with your thumb and push it all the way to the bottom of the primary or secondary. Open it to suck up some yeast from the bottom. Moving it around while doing this also helps. Close up the end again and move the cane to your starter vessel and dump the yeast in there. Repeat this a few times until you have enough yeast.

At this point you can also used a different yeast than the one used for fermenting the beer. This may provide advantages. Lager yeast may be used during the colde months to allow conditioning of an ale at basement temperatures. Or a better flocculating yeast can be used to bottle a beer that has been fermented with a low flocculating yeast. In this case it is beneficial to drop out the initial yeast with a fining agent like gelatin. My Kaiser Alt is bottled this way.

Now wait until it starts fermenting.

Calculating the volume

While the calculation of Speise additions is easier, a precise calculation of the amount of Kraeusen needed is more complicated since its fermentation constantly reduces the amount of sugar that is needed. I’ll be showing a simplified equation and a more precise approach. A spread sheet also exists for the more precise approach. All calculations are done in weight % (basically equal to Plato) for the extract and g/l for carbonation. If you are want to use specific gravity and volumes of CO₂ you can use these equations to perform the conversion:

% extract = (SG – 1) * 4000

<g/L CO₂ = <Volume of CO₂ >* 2

simple equation

This is a simplified equation for the needed Kraeusen volume. It assumes

• 10% apparent attenuation of the Kraeusen
• 75% apparent fermentability of the Kraeusen
• The Krauesen volume is not significant compared to the beer volume

V_Kraeusen = 336 * ( C_final * V_beer - C_beer * V_beer - 0.5 * m_sugar ) / OE

• V_Kraeusen - The volume of Kraeusen needed in ml
• C_final - The final carbonation level that is desired in g/l
• V_beer - The volume of beer that needs to be carbonated in l
• m_sugar - The amount of sugar that is also added in g. Additional sugar may be necessary if the calculated Kraeusen volume is larger than what is available. When using DME, multiply this number with 0.66, which is a typical fermetability for DME.
• OE – The original extract of the Krausen in % or Plato

accurate equation

A discussion of the accurate calculation is shown at the end as it is rather long and would distract from the subject. Instead I want to focuss on the use of the spread sheet:

Bottling day

On bottling day you need to do the following:

• take a gravity reading from the beer that you are going to bottle (when using the spread sheet for calculations) • with a sanitzed spoon skim the Kraeusen off the Kraeusen beer. Not really necessary, but I like to do that. • Take a gravity reading from the Kraeusen beer (when using the spread sheet for calculations) • Fill-out the spread sheet and determine the amount of Kraeusen beer needed. Note that you will not be able to use all the Kraeusen beer that you have since you want to hold back the sediment. If you need more than you have, add some sugar. • Boil sugar if needed • With one pour (no tilting back) pour the Kraeusen beer into a sanitized measuring cup until the desired volume is reached. Make sure that you get as little as sediment as possible. The yeast in suspension is just enough. • Put this at the bottom of your bottling bucket • Rack the beer on top of it. Also make sure that it mixes well with the Kraeusen. • Once you have enough beer, add the sugar solution if necessary. Adding it to early could have scalded the yeast • Bottle as usual.

Conditioning

The bottles should carbonate within about a week at the fermentation temperature for the yeast that was used (10 C / 50 F for lager and 20 C / 70F for ales). This quick conditioning time is one of the benefits of Kraeusening. The beer may still benefit from additional aging though.

Kegging

The same method is used for carbonating my lagers in a corny keg before I start lagering. But there I just make sure that enough Speise is added to get above the desired CO2 level. I then monitor the pressure build-up and blow-off any excess CO2. This has the advantage of adding fresh and healthy yeast before the lagering is done. Finally I rack it off all the yeast into a serving keg.

Final Comments

Is all this extra work worth the effort? Every brewer has to decide this for himself. Maybe some day I will do a direct comparison between the same batch of beer carbonated with corn sugar, DME and Kraeusen.