In the first part of this article, I discussed the rationale behind kräusening — adding small volume of fermenting beer to a lager beer that has just finished fermenting. In this part, I’ll discuss how to do it at home. There are few different ways that a homebrewer can kräusen their beer. Essentially, there are three ways you can come up with the wort you need, and a few ways to be in possession of the required yeast. In the case of the wort, you can either withhold some wort on brewday or make the wort a few days before you plan to kräusen.
Witholding Kräusen Wort
If you plan to reserve some wort, you’ll need to withhold 10–20% of your batch size. For a 5-gallon (19-L) batch, this is 2.0–4.0 quarts (1.9–3.8 L). Collect the chilled wort prior to aeration and pitching. (If you have an in-line aeration stone, turn it off while you collect the kräusen wort.) Store it in a sanitized vessel in your refrigerator. PET soda bottles work fine for this. So do mason jars. You do not want this wort to start fermenting, so optionally put this vessel in a larger container filled with ice. The colder it is, the more biological activity will be suppressed.
Making “Quicky Kräusen” Wort
If you plan to make the kräusen wort, the easiest way is simply to boil some light malt extract. You’ll need to plan ahead to do this, however, so you don’t dilute the characteristics of your beer. For 5.0 gallons (19 L) of beer, here’s how to plan for an addition of “quicky kräusen.”
Formulate your beer as you normally would. Then, figure out how much base malt (or light malt extract), it will take to make the proper volume of kräusen wort at the same original gravity as your beer. (Alternately, if you’re brewing a strong lager and using the kräusen beer to aid in attenuation, make the kräusen beer at a slightly lower gravity. This will ensure that the yeast are more healthy and vigorous when you add them.)
Now subtract the equivalent amount of base malt from your 5.0-gallon (19-L) recipe and brew the main batch of beer so that that your fermenter volume is equal to 5.0 gallons (19 L) minus the volume of your kräusen wort. In this case, let’s say your kräusen wort is 10% of your batch volume. Thus, you’ll have 4.5 gallons (17 L) of beer that is slightly darker and slightly more bitter than your target, but at the target strength. When you add the kräusen beer to the main beer, you dilute the color, bitterness and flavors down to their original intended levels, but the original gravity remains constant. (This assumes you planned for the kräusen beer to have the same OG as your main batch. If your kräusen beer is lower in gravity, your main batch will be slightly higher than your target. And adding the kräusen beer will dilute it to working strength.)
Brew It Again
A third alternative, similar to how things would work at a commercial brewery, would be to brew the same beer again a day or two before you plan to kräusen. When the second fermentation reaches high-kräusen, withdraw some of the fermenting beer to kräusen the previous batch. Repeat this procedure then the second batch is almost done fermenting.
Once you’ve got the appropriate amount of kräusen wort, either chill or heat it to your fermentation temperature (or a few degrees above). Aerate the wort thoroughly, and pitch your yeast. The yeast can potentially come from several sources.
One way to have yeast for kräusening is to save some from your yeast starter. If you plan ahead and make your yeast starter 10–20% larger than required, divert 10–20% (as appropriate) to a sanitized container before pitching the bulk of the yeast to your main batch. Store the yeast in a sanitized vessel in your refrigerator. Do not store the yeast in a sealed container, as CO2 pressure can cause it to rupture. A beer bottle with a balloon rubber banded to the neck will work, as will any small vessel to which you can fit an airlock. If you’ve iced the starter wort, put the yeast in the ice, too.
The other option is simply to spend more money and buy two packs of yeast — one for the yeast starter and one for the kräusen beer. I suppose it would be possible to use dried yeast for the kräusen beer, although I haven’t tried it. Be sure the apparent attenuation is similar between the strains if you do.
If you use a cylindro-conical fermenter, a third option would be to collect some yeast from your main batch a few days before you kräusen. You would then need to revive it. For this, add very low-gravity (~SG 1.020), highly-aerated wort, and a pinch of yeast nutrients (for the zinc). Then pitch that yeast to your kräusen wort. But that’s a lot of work.
Once you’ve got kräusen wort at the appropriate temperature and the yeast you need, aerate the wort and pitch the yeast. Place the kräusen vessel next to your fermenter in your fermentation chamber and wait until it hits high kräusen (the peak of fermentation) or just prior to that. Your kräusen beer should be within a few degrees Fahrenheit (roughly 1.5 degrees Celsius) of the main batch, or the yeast will be shocked when mixed with the beer. Don’t add the kräusen beer until it is vigorously fermenting. If you added the aerated and pitched kräusen wort, you’d be adding oxygen to the main batch, and you don’t want that. In addition, don’t add kräusen beer while the main batch is still strongly fermenting. Wait until it stops, or slows to a crawl.
After kräusening, your batch will be lagered. And, you’ll want to separate the beer from the primary yeast before lagering. As such, adding the kräusen beer and racking to secondary at the same time will save you a step. The easiest way to do this it to add the kräusen beer to your secondary fermenter, then rack your main batch into it. Adding the kräusen beer when you rack also ensures that the CO2 produced will expel the oxygen from the headspace. Hold the kräusening beer at the previous fermentation temperature until all activity ceases, then proceed to lagering.
A Fine Ending
I’ve never tried it, but I would guess that, if you fine your beer with PVPP, you could kill two birds with one stone by adding the PVPP (Polyclar) powder to your kräusen beer.
Kräusening for Volume
In the first part of this article, I mentioned that commercial brewers use kräusening to completely fill their fermenters, leaving no empty tank space in the brewery. Homebrewers can also kräusen for volume. Just take the volume of one of your fermenters and multiply it by 0.20 to 0.20 (20%) to calculate how much room to leave for the kräusen (foam) during primary fermentation and later the kräusen wort. Then, formulate and brew your beer to occupy the remaining 80%. When it comes time to kräusen, fill the fermenter. Although the kräusen beer is fermenting, this fermentation is gentle compared to the initial fermentation and doesn’t raise much kräusen. An added benefit of kräusening for volume is that, by eliminating any headspace, you protect the beer from oxygen.
Capturing Carbon Dioxide
In the next installment of this article, I’ll discuss capturing the CO2 from kräusening to carbonate your beer.