Berliner Weisse through the ages – part 2: a fine line between aroma and spoilage

In the 19th century, Berliner Weisse could be found all over Berlin. However in the last few decades, it has been reduced to a niche existence. Recently, craft brewers around the world have rediscovered this traditional style of beer. In the second part of his article, the author focuses on the creation of this sour, top fermented beer and the importance of microorganisms to the beer’s flavor and quality.

By Dr. Peter Lietz, Berlin

Originally, the heavily carbonated, only slightly acidic lagers of the 17th and 18th centuries were either brewed from 100 % wheat malt or with a proportion of barley malt at varying intensities. The acid was produced by acid-forming bacteria within a few days. This bacteria could enter into the process in different ways: in the malt, the water, or the air.

Huguenot influence

At that time, top fermentation was used exclusively. In addition to the brewing yeast Saccharomyces cerevisiae, strains of wild yeast (Torula species) were involved in the process, as were lactic acid bacteria, usually in the form of contamination. Historical records do not precisely indicate the first time a sour weiss beer was produced. The first Berlin cookbook written by Johann Sigismund Elsholtz in 1682 is entitled Diateticon and supports the conclusion that a white beer was already being brewed in Berlin during the mid-17th century. One thing is certain, however: The Huguenot influence in Berlin is tied to how these white beers developed into what later became known as the typical Berliner Weisse. These religious refugees from France preferred the clear, lighter wheat beer produced in their own breweries; this beer contained approximately 5.7 % malt extract and a correspondingly low alcohol content of just under 2 %. The classic Berliner Weisse produced and marketed by specialized weiss beer breweries until the second half of the 20th century likely did not come into existence until the 19 th century.

Improper fermentation in the mashing process

In the late 18th century, wort was prepared in a similar way to the method still used later on in the 19th century. One important difference should be mentioned, however. In the late 19th century, brewers assumed that if they used unboiled mash, the cultured lactic acid bacteria would remain alive in the wort as part of the microflora in the malt. This was the only reason why they did not boil the mash and wort. It wasn’t until later that they realized that only a negligible amount of cultured lactic acid bacteria ended up in the wort – and, consequently, in the fermentation process – via the mashing process. However, this method also involved significant risk of serious contamination, particularly with unwanted Micrococci bacteria. Brewers attempted to avoid improper fermentation by increasing the mashing-off temperature to 85°C – and later, potential improper fermentation was countered by boiling the wort and using pure cultures.

Lactic acid bacteria during fermentation

In their work “Zur Kenntnis der stäbchenförmigen Milchsäurebakterien im Berliner Weißbier” (‘On Bacillar Lactic Acid Bacteria in Berlin Weiss Beer,’ 1909), Schönfeld and Dehnicke focused on the causes of different types of acidification. They isolated various lactic acid strains of the yeast species Saccharobacillus pastorianus from seven different breweries, then categorized these strains in three groups. During the weiss beer fermentation process, the lactic acid bacteria generally grew at a rate similar to yeast propagation; bacterial growth did not begin to slow until the beer reached an alcohol content of more than 5 %. The mashing process and hop addition had a significant impact. The propagating lactic acid bacteria and Pediococci had the least significant impact on the beer when hops was added to the mash. If the wort was boiled with hops, the mixture did not achieve the desired level of acidity. Apparently, the boiling process generated more antibacterial substances than boiling the mash with hops did. That’s why weiss beer brewers long shied away from boiling the lautered wort before casting and consequently risked the beer becoming ‘ropy.’ To reduce this risk of contamination, Schönfeld suggested heating the lauter wort to at least 85°C before casting and only then pitching the yeast.

From the collection of Michael Weidner

Torula yeast was common

The yeast mixture in Berliner Weisse consisted of a top fermented brewing yeast (Sacch. cerevisiae) and a high percentage of lactic acid bacteria (lactobacilli). Brewers either harvested this yeast mixture from their own brewing process, or they procured it from inns that harvested it from their own fermentation vats after completing primary fermentation. Weiss beer brewers wanted to achieve the lowest possible level of attenuation during the fermentation process, unlike the process for producing bottom fermented lager beers. For this reason, they preferred Saaz yeast strains, which were capable of breaking down dextrins during secondary fermentation. The need for a low level of attenuation resulted from the fact that many customers at the time preferred their beer to have a malty flavor, as Schönfeld noted in his book “Reinzüchtung und Versand von obergärigen Brauereihefen” (‘Growing and Shipping Pure Top Fermenting Brewing Yeast Cultures’) published in 1900. While the weiss beer yeast should very quickly become buoyant, the yeast cells that remain in the young beer should settle firmly at the bottom of the bottle after fermentation.

To preserve the flocculent character of the yeast during the ongoing production process, highly cured malts were used that were also supposed to lend the beer a ‘finer aromatic quality.’ Torula yeast was also a common contaminant, in addition to muciferous Sarcina bacteria. Today’s Brettanomyces was also categorized as part of this species. The term Brettanomyces was coined by N. Heltje Claussen in 1904; at the time, it referred to Torula yeast that simultaneously produced acids and esters to lend the beer a unique flavor, while fermenting dextrins at the same time. Paul Lindner (1861–1945) described these types of Torula yeast as the most common microorganisms in breweries at the time. They resulted in a stodgy taste in weiss beer, as well. He does not indicate whether this description always refers to Brettanomyces, but it is unlikely.

Breakdown of dextrins

In 1930, Lindner referred to the work of Morris, van Laer, and Hjelte Claussen, who pointed out the role that wild yeast plays in breaking down dextrins during secondary fermentation. In his own experiments with a Guinness porter yeast, Lindner was also able to verify the breakdown of these dextrins. It is safe to assume that he was working with a Brettanomyces yeast according to modern classification. However, it seems that he was also aware of the risk of contamination and promoted the selection and exclusive use of special top fermenting cultured yeast strains (Sacch. cerevisiae) to ferment dextrins. Lindner managed to isolate these types of yeast strains. However, later work by H. Haehn, M. Glaubitz, and W. Gross, published in the Wochenschrift für Brauerei in 1937, was unable to confirm his observations. They did not find any strains of top fermenting brewing yeast that could ferment dextrins.

From Glaubitz, M. and Koch, R.: “Atlas der Gärungsorganismen” (‘Atlas of Fermentation Organisms’), 1956 – Brettanomyces yeast, very old cells from porter beer sediment (500 x magnification)

It is possible that the old weiss beer samples were contaminated. Although it is not mentioned in older literature, S. diastaticus could also have broken down dextrins with lower molecular weight during secondary fermentation. S. diastaticus was first described as an independent species by J. Andrews and R. J. Gilliland in Volume 58 of the Journal of the Institute of Brewing in 1952. Today, it is classified as a sub-species of S. cerevisiae. Recently, this yeast has played a rather disreputable role in bottom fermented beers, as – like S. pastorianus – it produces significant CO2 and haze during secondary fermentation, even in filtered beer.

Storage impacts flavor

Filling the weiss beer into bottles also posed a major problem. The beer would be bottled shortly before the end of fermentation – sometimes in the brewery, but often, the bartenders would do it themselves, and not always in the most hygienic conditions. A secondary fermentation period of 8 to 14 days was sufficient to ensure the formation of the necessary carbonic acid pressure. Stronger beers with up to 16 % extract were often brewed at the end of the actual weiss beer season, around the end of summer. These were stored for longer than the obligatory 14 days. These bottles were stored in the cellars of the inns, sometimes for months or years, buried in sand to maintain a stable temperature. This created a highly carbonated, aromatic beer that connoisseurs regarded highly, giving it nicknames such as ‘champagne weiss.’ We cannot rule out the possibility that in addition to the cultured yeast used in the brewing process, wild yeasts that could break down dextrins with lower molecular weight also impacted the beer during the long storage period. These champagne weiss beers had to be stored in bottles for at least six months to allow their well-rounded flavor to fully develop. If the beers were stored for longer periods of time, such as years, however, the flavor could turn sour and the beer would develop an unpleasant aroma. Lindner and Schönfeld had already pointed out these risks, which were primarily the result of wild yeast. For this reason, they recommended using special strains of yeast with significant capacity for secondary fermentation.

Pure cultures

Losses occurred repeatedly as a result of contamination, particularly in batches of weiss beer that had been stored too long, so brewers began working with pure cultures of yeast and lactic acid bacteria at an early stage. According to Schönfeld, however, these attempts were not always successful. In experiments involving top fermenting pure yeast cultures mixed with lactic acid cultures, the cultures quickly separated. Often, this was not conducive to the quality of the beer. Replacing L. pastorianus with the cultured lactic acid bacterium Bacillus delbrückii according to the method proposed by Francke did not deliver satisfactory results, either – Schönfeld described the process in his article “Die künstliche Säuerung des Berliner Weißbieres” (‘Artificial Acidification of Berlin Weiss Beer’) in the Wochenschrift für Brauerei in 1909. Acidification did occur; however, the character of the beers produced using this cultured lactic acid strain deviated significantly from the traditional weiss beer.

From Henneberg, W.: “Gärungsbakteriologisches Praktikum, Betriebsuntersuchungen und Pilzkunde” (‘Practicum in Fermentation Bacteriology, Facility Inspections, and Mycology’), 1909 – Saccharobacillus p. var. berolinensis (weiss beer lactic acid yeast), cells from beer and mash. a: Normal cells, a1: Granulated (i.e., dead) cells, b: Cells with globular Plasma, c: Cells with segmented Plasma, d: Hypertrophic cells, simple preparations e, e1: Segments of a cell chain from larger bonds in a drop culture (2000 x magnification)

The importance of Brettanomyces yeast

Frank Methner also addressed the optimum composition of microflora in weiss beer fermentation in his dissertation Über die “Aromabildung beim Weißbier unter besonderer Berücksichtigung von Säuren und Estern” (‘On Aroma Formation in Weiss Beer, Taking Acids and Esters into Particular Account’) presented at TU Berlin in 1987. His research was based on numerous old bottles of weiss beer taken from various Berlin breweries in the 1970s and 1980s, as well as samples from the production process. In his biological evaluation of the sediment, he found S. cerevisiae (top fermenting brewing yeast) and S. carlsbergensis (bottom fermenting brewing yeast) in a few samples, as well as Candida crusei and Aureobasidium. Brettanomyces bruxellensis, on the other hand, appeared in nearly all the sediment samples. The available data does not indicate whether the samples contained exclusively B. bruxellensis or B. claussenii, which is known for producing a characteristic aroma. Given the dominance of Brettanomyces, Methner postulated that this yeast (which is primarily found in porter beers) was mainly responsible for the formation of the typical Berliner Weisse aroma.

In his dissertation, Methner chiefly focused on the formation of the aroma compounds responsible for Berliner Weisse’s characteristic flavor. He carried out fermentation processes on a small scale using the microorganisms isolated from various weiss beer samples. Methner studied bottled beers of different ages, as well as samples from his own attempts at brewing – which were unfortunately only supported by minimal microbiological test data – and came to the following conclusion: “The fact that the Brettanomyces bruxellensis species of yeast – which also stays alive in the bottle over a longer period of time – was found in the majority of Berlin weiss beers indicates that this microorganism is vital to the production process of this beer and is decisive in shaping its character. The influence of lactobacilli, on the other hand, is limited to the acidification process. The yeasts involved are exclusively responsible for aroma formation; Brettanomyces (...) is responsible for the lion’s share.”

Brettanomyces and contamination in beer

This hypothesis certainly demands some careful scrutiny. Methner’s study results lead us to the conclusion that alongside other strains of wild yeast and lactobacilli, Brettanomyces could have caused contamination in the beer brewing and filling process in the 20th century, as well. His analyses also indicate that this contamination could survive longer storage times of several years, unlike top fermenting cultured yeast (S. cerevisiae) and lactobacilli. This was to be expected if we take into account the comprehensive research done by VLB long ago, during the early years of the organization’s existence, especially VLB’s work on top fermentation. We know that B. bruxellensis cannot assert itself against S. cerevisiae during primary fermentation or in the first phase of secondary fermentation. Later, however, when the cultured yeast has largely completed its metabolism and the cells have died off, B. bruxellensis begins to grow again, similar to a bottom fermented beer contaminated by S. pastorianus – and this often has serious consequences. If the beer wort in combination with the yeast mixture is contaminated in this way, the contaminated young beer will usually appear completely fine during fermentation and the first few weeks of maturation, as the author could observe in his own work. This type of contamination begins to spread after several months of storage when the cultured yeast completes its metabolism. As a result, the beer turns sour and becomes undrinkable. This phenomenon is described repeatedly in documentation from the heyday of weiss beer production.

Willner Brauerei (brewery) in Berlin-Pankow, ca. 1935–1940 (from collection of K.-H. Pritzkow)

From 1923 or so onward, Berliner Weisse was primarily brewed as a traditional, light summer beer and was ready to drink after a relatively short fermentation and maturation period. This left no time for sluggish Brettanomyces to assert itself against the top fermenting yeast and play an active role in the beer’s flavor. If these beers had been brewed stronger and stored in bottles for months or years, B. bruxellensis – in conjunction with other acid-resistant microbes – would certainly have had the opportunity to develop and influence the flavor. Whether it always improves the flavor is another question, of course. Methner’s extremely interesting results regarding aroma formation in weiss beer prove that the Brettanomyces yeast cells that enter the beer as contamination survive in weiss beer for years and can significantly influence the aroma. In the process, more esters and volatile and non-volatile carboxylic acids are formed. This can improve the aroma over the short term, but it can also spoil the beer. Contamination of this nature is impossible to control in normal brewery operations. The beers brewed exclusively using Brettanomyces as cultured yeast had an unconvincing flavor, as Methner himself says.

The 1st part of this article was published in the International Edition of Brauerei Forum (No. 5/2019). Part 1 focussed on the original composition of fermentation cultures and can be found online under www.vlb-berlin.org/en/brauerei-forum/BF5_2019.

Comprehensive information (in German) on this subject is available in the book “Die Berliner Weisse – Ein Stück Berliner Geschichte” (‘Berliner Weisse – A Piece of Berlin History’), published by VLB Berlin and written by Gerolf Annemüller, Hans-J. Manger, and Peter Lietz