Excellent yeast article by De Dolle brewer

[seymour]

I just came across this great email response from Kris Herteleer, head brewer of De Dolle, one of my favorite Belgian breweries. It's from 2005, so fairly outdated, but still extremely interesting.

RE: What Happened to Oerbier Since 2000?
Kris Herteleer
De Dolle Brouwers, Esen, Belgium

At the end of 2000 our source of yeast had disappeared. The yeast strain used for Oerbier & Stille Nacht had come from Rodenbach brewery in Roeselare and they had decided to not supply any yeast any more due to reasons of organization and practical reasons.

Since decades there were some breweries Rodenbach had supplied yeast to:
Trappists of Westvleteren who switched to Westmalle yeast after problems with unintentional sour beer. Felix in Oudenaarde who stopped brewing in 2001. Another famous brewery using Rodenbach's yeast was Liefmans. After the takeover by RIVA, Rodenbach stopped the delivery of yeast to them a couple of years prior to 2000.

The yeast of Rodenbach is very special and contains some different strains of bacteria other than Saccharomyces Cerevisea. They are Gram-positive and Gram-negative bacteria, some say even Brettanomyces, which other breweries fear and do not like in their installations. Brewers say "clean" beer and "sour" beer do not match, so no lager beer brewer will use that strain for due to a potential acid-type beer in the same brewery.

Supplying yeast to another brewery was also a token of camaraderie or at least congeniality knowing that small brewers do not have the installation nor the knowledge of treatment of yeast. There is also a kind of pride in delivering yeast to others, because if the smaller brewer didn't like the beer he wouldn't be interested in using the yeast.

Americans will say: the ultimate honor to a beer is to copy it! This may be a reason, too, they decided to keep the yeast for themselves! The brewery Rodenbach wrote a letter in November 1999 saying that the yeast supply would stop on December 1, 1999. Considering this was a weekend, it was very short notice. We had heard rumours to that effect so we had stock-piled some yeast. By the time Palm took over Rodenbach I had such a strong feeling the yeast supply would not be eternal, but it seems that Palm has nothing to do with it. If Rodenbach had been taken over by Heineken, for instance, would the yeast supply not have been ceased? Whatever the case, we were happy to have had the opportunity of using Rodenbach's yeast for over 20 years and we therefore respected their decision. Some American beer lovers were very angry and wrote emails to Palm to "force" them to continue their yeast supply...but here in Europe, things don't work that way!

As I had done tests with Oerbier wort with other strains, which were not convincing, I thought the best thing would be to keep reusing the old yeast. For a single strain, that would be a good method, but with that complexity of the Rodenbach multi-strain yeast soon some unexpected things happened:

The alcohol by volume of Oerbier increased from 7.5 % to 10.5%. For Stille Nacht--the gravity of which is even higher--it increased from 8% to about 12%. With problems of refermentation as a result! What also changed was the balance of acidity. The bacteria had disappeared. So we likely ended-up with a mutated strong single-strain yeast, and no more bacteria.

There were other strange things happening as well. The refermentation of a batch of Stille Nacht seemed to NEVER end and the last three pallets of that beer had bursting bottles all over, even in December with the colder temperature! As I could not longer stand the exploding bottles, it was high time to find a solution!

We poured the beer into wine barrels and after 12 months bottled them as Stille Nacht Reserva 2000. The attenuation dropped to 1000, even lower, and the taste was really something exceptional. The empty barrels were then refilled with Oerbier so we had Oerbier Special Reserva one year later. With the Reserva series we had so much time that sometimes it matured for over two years in the barrels, thinking that it could only get better by the passing of time. This may or may not be so. Up to now, though, we have not had one bad bottle of Reserva.

Since 2000 we were looking up in beer books how the fermentation of old-fashioned beers really went on, with the special strains such as Lactobacillus, Pediococcus, Brettanomyces and others. We had to know what these strains liked, what they did not like, how they grew and what their behavior was when exposed to yeast. And that's exactly what happens in wine as well.

So we went through wine books and literature of Lactis bacteria as well as the history of English and Belgian beers in the 19th century. Together with a guy (probably sent from heaven!) who works in microbiology of lactic bacteria used in bread, We installed a fermentor to grow yeast, yeast that we had cultured from old kegs of De Dolle Stille Nacht that were returned from Finland.

Some kegs were not empty and the beer was delicious. The kegs were very old, thus containing the original Rodenbach balance of yeast and bacteria. To us, this could not have been more fortuitous. We then started to reculture this yeast.

The taste of Oerbier had changed. It was dryer, heavier and the balance of caramel malt was disturbed due to the disappearing of the maltier HUYS. So we adjusted that - and for the acid taste we went back to a tradition of old Flemish beers, which is to let beers sour slightly with a controlled lactic acid baterial fermentation.

The first four brews were sold and marked for the USA by a white cap with "SPECBREW2005" on it. The first two pallets were less sour than the second shipment to the USA marked "SPECBREW02". This is due to a larger amount of "sour" beer in the blend. We think the more sour beer should be our final version, though some variations may occur.

What are the reactions of our customers? They all taste the difference, most of them like the sour taste over the sweet one. My mother-in law prefers it sweeet! She says that there will be some time needed to get accustomed to it. Whatever the case, we must use the liberty of being small and follow our own taste of what beer should be.

The alcohol by volume is now 9% which is still 1.5% stronger than the "old" Oerbier. It is dryer, too, due to the stronger yeast. The acidity should be about the same. In terms of aging, no problems are foreseen.

If you have other questions, the answer lies in your glass!

Cheers,

Kris Herteleer
De Dolle Brouwers

[Scotty]

A nice little read. It's refreshing to hear a brewer explaining the reasons why a beer has changed as opposed to flat-out denying it.

[seymour]

I agree. I also liked that he abstained from bad-mouthing Rodenbach and it's new parent company. As it turned out, necessity was the mother of his invention...and we all get to benefit from the unique new results!

[Scotty]

sadly, I never got to try any 'Rodenbach' versions but the current range is superb. Still loads of yeast-derived flavours that I would come to expect from a Belgian beer.