Revision as of 14:56, 17 January 2009

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 with 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 OE (original extract) 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 starting gravity)
• 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 time will also be more predictable because fresh yeast is added. Since carbonation takes only a few days to a week, as opposed to weeks, the beer can be aged longer in bulk while it takes the same amount of time from kettle to glass.
• you will have more beer to bottle and can get 5 gal 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 Whirlpooling 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 use a different yeast than the one used for fermenting the beer. This may provide advantages. Lager yeast may be used during the colder 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 spreadsheet 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 more accurate way of calculating the carbonation that can be achieved with various priming agents is done here: Accurately Calculating Sugar Additions for Carbonation

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 sanitized 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 will be plenty for carbonation
• Place the Kraeusen beer 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 in the bottling bucket, 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

I may use the same method for carbonating my lagers in a corny keg before I start lagering. But in this case I just make sure that enough Kraeusen 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/herself. Though it seems more complicated, the additional steps don't add much overhead to bottling for me since most of the time is spent bottling anyway. I like that the beer will be ready within about a week after bottling. Using the spreadsheet and measuring the actual attenuation of the Kraeusen removed the worry of having the Kraeusen beer attenuate to far.