Thursday, 19 February 2015

German brewing in the 1970’s – fermentation

We’re finally getting to the vaguely interesting bits of this article. Though obviously that’s interesting only in a relative sense.

Let’s dive right in with an explanation of the classic German method of fermentation: open, without artificial fermentation

Technology of Fermentation and Maturation
It has been known for a long time in Germany that raising the carbon dioxide content from, for example, 0.30% (w/w) to 0.50% (w/w) by artificial carbonation causes no problems. Most breweries still use open fermentors and are unable to re-use the fermentor carbon dioxide, but the German beer laws demand that carbonation of beers is effected only with the carbon dioxide evolved during fermentation of the same brew and so-closed fermentors are necessary when beer is produced by non-conventional methods requiring carbonation of beers.”
Journal of the Institute of Brewing, Volume 83, Issue 1, March-April 1977, page 76.

I’ve mostly been around quite small Bavarian breweries. But every single one still had open fermenters. Even ones with a brand new brewhouse. Which tells me something: that there’s no artificial carbonating going on. Carbonation is achieved by bunging the lagering vessel and allow CO2 to build up naturally through the action of the yeast. As the temperature drops, more CO2 can be dissolved by the beer.

There are some truly weird bits in the Reinheitsgebot. Only allowing artificial carbonation with the CO2 produced during a beer’s own fermentation is one of the weirdest. It sounds like a fudge to me. That brewers wanted to carbonate artificially and this was a way to achieve that without using any extra ingredients.

Here’s a description of that carbonation process:

“Table XII compares various procedures for fermentation and maturation. In the classical method of primary fermentation and lagering, the residual extract of the beer after primary fermentation is about 3-5% (w/w). During lagering about 1-3% of this remaining extract is fermented, so that the finished beer contains about 2-0-2-2% of extract. The carbon dioxide generated during the lagering stage serves to purge the beer, improve the separation of precipitated proteins and tannins and to increase the carbon dioxide content of the final beer from about 0-25% w/w to 0-50% w/w.”
Journal of the Institute of Brewing, Volume 83, Issue 1, March-April 1977, page 76.

Here’s an overview of the four main systems around at the time:

TABLE XII. Comparison of Fermentation and Maturation Systems.
Method Primary fermentation Transfer Lagering
Classical 7 days at 9°C Beer with 3-5% residual extract cooled to 4°C 35-50 days with temperature reducing from 3° to 0°C
Using Kräusen 7 days at 9º-10°C Beer with 2% residual extract cooled to 4°C. 10-12% Krausen with 8% residual extract added 14-28 days with temperature reducing from 4° to 0°C
Under pressure at high temperature (Champagne Wheat Beer) 3 days at 16°C or 4 days at 14°C under pressure Beer with 2% residual extract 2.0 bar pressure cooled to 0°C 7-14 days stabilization at 0°C 
Modern development 7 days at 12-14°C with CO2 collection Attenuated beer carbonated and cooled to 0°C 14-21 days stabilisation at 0°C and final carbonation

This is a method which had been around since the 19th century – adding fermenting wort, or Kräusen, to the maturing beer. It was popular in the USA, and not just amongst bottom-fermenting brewers. Amsdell of Albany kräusened their top-fermenting beers around 1900.

“The Kräusen method is used especially in those breweries where fermentation takes place in cylindro-conical vessels and maturation in classical horizontal lagering tanks. Since it is difficult to estimate the yeast concentration of green beer fermented in a cylindro-conical vessel it has been found advantageous to leave the beer in the vessel until no fermentable extract is left and the dispersed yeast cells are at a minimum. The green beer is then drawn off and Kräusen, which contains a fermentable extract of about 8-9% w/w and about 40 million yeast cells per ml, is added equivalent to 10-12% of the beer volume. This procedure is simpler to control than the classical method of leaving a certain amount of extract and also has the advantage that beers produced in this way may be filtered and bottled after only 21 days. The only problem with this method is that Kräusen with 8 % extract is not available every day and the beer has to remain in the vessels for different times until transfer. As a result, the fermenting cellar has to have a greater capacity than that calculated for the classical method.”
Journal of the Institute of Brewing, Volume 83, Issue 1, March-April 1977, page 76.

Now isn’t that interesting? Kräusening was used because they needed to ferment the beer right the way down in the conicals. The British equivalent of this was to prime beers with a high-gravity sugar solution at racking time. Though Guinness did use high-gravity fermenting wort.

Champagne wheat beer is Kristallweizen. Not something I’ve ever cared for, myself. It always seems thin and rather dull, with the spiciness from the yeast rather subdued.

“We use the pressure fermentation method in Weihenstephan to produce the so-called 'champagne' wheat beer and it is obvious that our classical method using top fermentation can also be used with bottom fermentation. Green beer with a residual extract of about 5 % is pumped into closed fermentors, until a pressure of 2 bar is reached and the fermented beer contains 0.8 % w/w of CO2. This beer is cooled to 0°C and is then transferred to a 'stabilization tank' at a temperature of 0°C. After remaining in this tank for 7-14 days the beer is filtered and bottled. The advantage of this procedure is that the carbon dioxide originating during the fermentation from 5% residual extract to 2% residual extract is saved to carbonate and purge the beer. The disadvantage of the procedure is the necessity to have pressure tanks which can sustain a pressure of 2 bar but the costs of these pressure tanks are naturally not as high as the costs of installing carbon dioxide collection equipment. No modern brewery, however, will demand pressure fermentation but will collect all the carbon dioxide evolved during primary fermentation not only for carbonation but also for pressurizing intermediate tanks or filling evacuated bottles on the filling machine.”
Journal of the Institute of Brewing, Volume 83, Issue 1, March-April 1977, page 76.

So in this method they conducted the final stages of the fermentation in closed pressurised fermenters, which again allowed the beer to carbonate naturally from the CO2 being produced. No need to collect the CO2 and then add it back in the form of artificial carbonation.

More fermentation next time.

No comments: