Friday, 25 April 2008

Berliner Weissbier - the long version (part 7)

This post is for Mike. He was disappointed that I'd interrupted my marathon series of Berliner Weisse posts just to write about my holidays. Don't worry, Mike. I'll carry on to the bitter end. After attenuation, yeast and bottled Weissbier, there's still yeast-free Weissbier and illnesses of Weissbier.

Attenuation
During primary fermentation, the attenuation of a 9-12º Balling wort is 66-75%.

The high degree of attenuation is due to the yeast, a high-attenuating of the Frohberg type.

The attenuation is also helped by the diastase that remains in the wort which, in conjunction with CO2 and lactic acid, breaks down the maltodextrins into more easily fermentable sugars.

As the level of acidity rises, it destroys the diastase, so this is only active at the beginning of fermentation.

Yeast
Because the pitching yeast consists of two completely different organisms, the usual methods for handling yeast cannot be employed. Washing and schlämmen disturb the ratio of yeast to bacteria because, being lighter, the bacteria is easily washed away. Any reduction in the amount of lactobacillus reduces the amount of lactic acid produced in the fermenting tun.

Weissbier yeast doesn’t keep or transport well. The Stoffwechsel products from the bacteria damage the yeast. Also the yeast generates protein-splitting enzymes within the yeast cells which eventually destroy them. These two factors mean that Weissbier yeast is more quickly susceptible than other top-fermenting yeast to Zerfetzung and Verflüssigung.

Because of the above, yeast which has lain for several days is not as effective as fresh yeast.

The best yeast for pitching is that collected from a fermenting tun and put directly into fresh wort. Yeast shouldn’t be collected at the end of fermentation as this is more likely to be infected with acetic acid bacteria or sarcina bacteria.

1 comment:

Mike said...

Thank you very much for this. My brewing kit has been sitting on idle for several weeks while you have been flogging around Europe. The hamster is exhausted and now he can finally put his efforts to good use.