To Vrai or Not To Vrai - Another White Labs Controversy?

The Short Version

Brewing practices in both home and commercial breweries have undergone somewhat of a revolution over the past decade, leading to a cohort of brewers who approach brewing from a much more technical & microbiological perspective. As a direct consequence of this, some commercial yeast products have been revealed to be other than what the manufacturers have stated - in at least some cases, with the manufacturer themselves being unaware that their product was a yeast/bacteria different from what they believed they had. In this blog post we reveal that the yeast sold by White Labs as Brettanomyces vrai (WLP648) - ironically a yeast mis-identified previously by the same manufacturer - is, in fact, a blend of two different yeasts - both are Brettanomyces bruxellensis, but are separate strains...although strains which appear to have evolved from a recent common ancestor.

Some Background

Brewing practices have changed dramatically over the past decade, with procedures such as sour worting, wild captures, and home/brewery isolated yeasts going from rare experiments to commonplace brewing practices. This change in brewing practices has led to some issues with commercially sourced yeasts - as one example, the growth of practices such as sour worting have revealed yeast-contamination issues in packaged "pure" strains of Lactobacillus. Similarly, the more microbiology-centric practices of home and commercial brewers has led to some unexpected revelations, including identification of "Brettanomyces trois" as a unusually flavourful strain of conventional brewers yeast (Saccharomyces cerevisiae). I was part of that effort, and the results of my and others work in identifying this yeast are the subject of a previous post. According to the manufacturer, this mis-identification was due to a chance contamination of "Brett trois" by this strain of Sacc, leading to the release of the "correct" strain of Brettanomyces, under the 'vrai' (French for 'true') strain name.

But is the strain name accurate - is this truly a pure strain of Brettanomyces? Most of us assumed so, even though this strain shows some characteristics when used as a pure culture for primary fermentation that run contrary to how most Brettanomyces behave when used for primary fermentation. When used in primary fermentation, most Brettanomyces act much like Saccharomyces - they rapidly ferment the wort, usually leave some residual sugars behind, and don't evolve over ageing as much as beers do when Brettanomyces are added during secondary fermentation - e.g. there is a lack of phenol production and super-attenuation. Beers brewed with WLP648 do ferment out fairly quickly, but tend to be more highly attenuated than beers brewed with other strains of Brettanomyces as the primary yeast. In addition, beers brewed with WLP648 also show some development during ageing similar to that of beers with Brettanomyces added to secondary - i.e. emergence of phenolic "funk", and additional attenuation of the beer. So is WLP648 simply a more aggressive Brettanomyces than other common brewing strains, or is something else going on?

To our knowledge, it was assumed by other brewers that Brett vrai was simply a somewhat more attenuative strain of Brett - that is - until my friend and brewing collaborator (and co-author of this blog post) Devin streaked WLP648 on a wort-agar plate. Initially, the plate appeared as one would expect of a pure culture - all colonies on the plate appearing similar in size, shape and colouration. But over a longer incubation time smaller colonies began to appear between the larger colonies, leading us to speculate that there may be a second strain of yeast in WLP648.

Using a combination of classical microbiology, microscopy, gene sequencing and test batches, Devin and I explored the two strains of yeast present in WLP648, demonstrating that Brett vrai contains two unique strains of Brettanomyces bruxellensis, strains which share a relatively recent common ancestor, but are otherwise quite different in their morphology and brewing characteristics.

Experimental details can be found below the fold.

My Warm Lagering Method

I must apologise about my poor blogging output over the past year or so, but there have been some big changes behind the scenes which have got in the way of my blogging and brewing...but I've not been completely inactive.

As my regular readers may recall, I've done some test brews using a newer "lagering" method in which lager-style beers are produced using lager yeasts fermented at ale temperatures (post 1, 2, 3 and 4). Motivated by these successes, I've brewed over a dozen lagers using this method in order to refine this process, with my last two batches produced using the same refined method. The first of these was a German-style pilsner; specifically the "Myburger" Bitburger clone from "Brewing Classic Style". Not only was it delicious, but I had trouble telling it apart in side-by-side tastings from its commercial cousin. The second beer was a doppelbock, and was everything I'd expect from the style. The take-home lesson from those two brews is that you can make very good "lagers", true to style, without the need for prolonged cold fermentation. Indeed, the Pilsner was 2 weeks grain-to-glass, and a month for the doppelbock.

All the gory details are below the fold.