In the following article, I will clear up some doubts and answer questions about the problem that arises when the Krausen, a foam formed on the surface of the wort as a result of vigorous fermentation, does not drop to the bottom of the fermenter over the course of days, or even weeks, if this is something that you should worry about, if you can bottle your beer even if it still has Krausen on top of it, and more.
So, without any further ado, let’s get started!
What happens if the Krausen doesn’t drop?
Krausen not dropping to the bottom of the fermenter is not a big problem in itself, because what really matters to us is that the fermentation is completed in a healthy way which is measured by taking gravity readings.
That said, there are some situations in which the Krausen is not likely to disappear over time that need to be clarified.
- Contamination: in the case of poor fermenter hygiene, for example, problems like this can occur. The krausen will remain active as the contaminating bacteria or wild yeasts would produce a refermentation. This would be the biggest cause that can keep the Krausen from dropping over time.
- Large amounts of hops: In highly hopped beers, the Krausen may have difficulty being absorbed, even more so when dry hopping during the primary fermentation.
- High protein worts: when fermenting worst with adjuncts such as oats, for example, a thicker and longer lasting krausen is produced because of the high level of protein in the wort.
In general, how long does the Krausen last?
This depends on the yeast strain used, whether it is Ale or Lager type, high or low attenuation, etc.
In general, we could say that Krausen begins to form when the yeast passes the dormancy phase and begins the reproduction phase (first 12 to 36 hours) and should disappear as the yeast cells drop to the bottom and the main fermentation ends and maturation begins.
In the case of Ale yeast strains, the Krausen is much greater and appears faster (it can start within 12 hours) and lasts from 2 to 6 days in most cases.
On the other hand, in Lagers or bottom-fermenting yeasts, the activity is much slower, so a smaller and lighter Krausen is formed, which can last from 4 to 10 days.
Is fermentation still active as long as there is Krausen?
Under normal parameters and if there are none of the above-mentioned problems, YES.
But as we already know, there can be situations in which fermentation is no longer active and yet the Krausen is still on the surface of the wort.
What happens if the Krausen drops too soon?
If for some reason this happens, fermentation will be incomplete, resulting in serious problems with the taste, aroma, and appearance of our beer.
Going further, the fermentation problems we could have if this happens could be:
- Formation of higher alcohols.
- Sub-attenuation of the wort.
- Poor absorption of diacetyl and acetaldehyde.
How to know if fermentation is really finished
To know if the yeast has completed its fermentation process what we have to do is to monitor the PH and gravity throughout the whole process.
The first thing to keep in mind is the attenuation power of our yeast and the target gravity we are aiming for.
Knowing this, the PH should decrease at a high rate for the first few days and then decrease more slowly until it stabilizes.
As for the gravity, taking two readings 24-48hs apart where it stays stable and doesn’t drop from one reading to the next indicates that fermentation is complete.
Forced fermentation test
There is a test we can perform to find out exactly what final gravity our beer can reach, also known as the forced attenuation test or attenuation limit.
It consists of extracting an aseptic sample of aerated and inoculated (ready to ferment) wort, which is large enough to allow for a specific gravity test and any other tests you wish to perform.
You are going to force the fermentation to reach its maximum attenuation through high temperature and constant stirring. The result is usually a slightly lower final gravity than the main (in tank) fermentation.
Procedure:
- Collect a sample from the fermenter
- Place on a stir plate (if available) at 80°F (27°C).
- Once the activity stops, take a specific gravity reading. This should be the minimum density that the yeast inoculum can reach in that wort.
This proof should reach the final gravity a lot faster than the main fermentation (in about 30 minutes).
You can use this information to help make decisions about fermentation in the fermenter. If fermentation seems to stop early, you will already know what the possible attenuation limit is.
If you need to make temperature adjustments depending on the percentage of attenuation, you will already know beforehand which value represents 100% of it.
Can I bottle even if there is Krausen?
This is not at all advisable, since the remaining yeast cells inside the bottle can generate an unwanted fermentation which will give us unpleasant flavors and aromas in addition to an unfavorable haziness in the appearance of our beer.
The only caveat would be if we are using a natural carbonation method called “Bottle Conditioning” in which the yeast in suspension is trapped in the bottle and generates Co2.
Conclusion
Fermentation is the most important and fundamental stage of the whole brewing process. The slightest mistake we make at this stage will seriously influence the final product.
In order for the yeast to have a healthy and trouble-free cycle, special attention must be paid to process times and temperatures.
It is recommended to take regular samples of the wort to know exactly at what stage the fermentation is in order to apply the correct criteria.