Expert: Alan Ward - 11/28/2006

Question
Hi Alan,
I've been reading through some of your recent answers to questions and in one of them you say that on occasions you leave your beer in the secondary fermenter to mature for several weeks. I assume that in these cases you need to re-seed with fresh yeast the beer when you come to bottle it? After how long do you think krausening is necessary, i.e. how long does it take for the active yeast to die?


Regards,



Gavin


Answer
Kräusening is the traditional method that German brewers use to carbonate their beer, most often lager beers. Basically, the process consists of adding freshly fermenting wort to beer that is ready to bottle. Kräusening overcomes the problem of yeast going dormant during the lagering phase of fermentation. It also helps clean up the flavor of the beer by reducing levels of diacetyl, acetaldehyde, and dries out the beer.

Usually when I leave the beer in the secondary it is a larger and the temperature is between 50 and 33 degrees.  For example when I do my Marzen we follow the traditional time period of brewing in March and bottling in September.  I have never added yeast to the batch after the original addition.

I have left a higher alcohol batch for six weeks with out adding more yeast.  An important factor is that all of my fermenters are either largered or store at room temp at 72 to 76 degrees using AC.

To get back to your question it really depends.  That is to say it depends on the yeast, temperature and storage (exposure to sun light).  If in doubt you can always add more yeast.  More than likely your yeast is alive but dormant.  It is important to remember that if the yeast use up all of the sugar it will go dormant or sleep waiting for more sugar.  This is why we add bottling sugar.  This addition of just a little bit of sugar gives the yeast something to feed on and thus produce CO2.  I have even harvested yeast from some commercial styles of beer (those that do not pasteurize) and those could have been on the self as long a year in some cases.

It may also be important to state that I always use a new yeast and I use a yeast nutrient for each batch.  I also use starter batches for my yeast most of the time except if I am using White labs.  It is always good practice to use a starter I just get lazy some times.

Basically if your getting low carbonation you may need to Kräusen.  If your getting plenty of CO2 then your fine.

Alan