Time & Yeast: Brasserie Thiriez

On my first day at Brasserie Thiriez last week I spent a solid chunk of my time labelling by hand a batch of bottles whose labels would not cooperate with their labeling machine. The beer was called Train to Mars and about half of it was heading to the States via Shelton Bros and the other half going to a bottle shop in Paris the next day. After a few hours I started to read the label and its subtitle caught my eye…

“A Saison de Mars hopped with Mosaic, Aramis, Simcoe and fermented with the world famous Thiriez house yeast.”


Here is a photo of the label,

some tagline
some tagline…


As a brewer, I have used a *very* similar strain for dry, hoppy saisons in the past with some pleasant results. In fact, it was the yeast that led me to Thiriez in the first place by way of Jester King.

However, I don’t think I realised until then how prominent the strain was worldwide. If you wish to know more about its influence, All About Beer posted an article last month here.

So here I was at Thiriez, having the opportunity to ask every question about the strain and fermentation I could think of. You should see my notebook now, nearly every page with some scribbling of some temperature or trick. However, the two things that struck me most about Thiriez were the yeast itself and the fermentation times.


Daniel in front of the taproom and old brewery
Daniel in front of the taproom and old brewery

When I learned to homebrew I was told that my beer would ferment for 5-14 days after which I could prime it, bottle it and await a further 2-3 weeks for a secondary fermentation in the bottle for carbonation. I tend to think that most English speaking home brewers learned something similar. In the professional craft-beer industry, a fermentation time of 5-10 days would be normal if not even a little long. I can’t help but think that the sheer number of pro-brewers starting as home brewers has largely influenced this for all intents and purposes industry standard.

So when I got to Thiriez, saw 6 tanks and quickly did some math I assumed that Daniel would be  brewing at least 3 batches a week. Then I had a look around at the temps of these tanks and the documented information. Some of these beers were brewed 3 weeks beforehand and were not even crashed yet! [crashing referring to chilling to near-freezing temperatures to assist with flocculation and beer clarity] When I started talking to Daniel about this ‘inefficiency’, it completely changed the way I saw clean pure culture fermentation.


Daniel selected his strain from a lab in Brussels when he started his brewery. He knew the qualities he wanted and the lab grew up a few cultures for experimentation. The one they chose was a single strain, meaning it is not a proportional mix of a few different cultures; rather, a single cell slowly grown up into pitchable quantities. It’s a Saccharomyces cerevisiae strain, so it’s not what we might call ‘wild’ producing funky flavours.

The yeast has gained popularity for its versatility and the flavour compounds it produces. The All About Beer article covers this well. Daniel uses his yeast for almost all of the beers he makes. the blond, ambree, hoppy blonde, 2.9% table beer, white and most of the seasonals are all fermented with the strain. While there is an unmistakable house flavour, each beer has its own yeasty nuances none too overpowering which varying from banana-clove in the White to a spicy pepper in the table beer. It’s pretty amazing tasting these side by side and seeing what this strain can do. A yeast like US-05, the dry Safale American ale strain, has nothing on the Thiriez yeast’s subtlety and variation. However, the main factor in these flavours comes from differing fermentation schedules harnessing or releasing certain compounds at certain temperatures to create the trademark Thiriez balance.

Top of the brewhouse and 4 40hl FV's
Top of the brewhouse and 4x40hl FV’s


As I mentioned before I was initially shocked to see how long Daniel’s beers spent in the tank. The normal fermentation time at Thiriez is four weeks before packaging then another two weeks following for bottle conditioning, 2-3 times longer than your standard APA/IPA brewpub or brewery. Daniel’s reasoning for this comes largely from a respect and care for his yeast. After 18 years working with the same strain, he does not like to shock it with quick temperature changes which stall the yeast’s work. Additionally while the major bulk of fermentation has completed in less than 5 days, he allows the yeast more time at slowly decreasing temperatures to continue its conversion resulting not only in a drier beer but also encourages the gradual consumption of harsher compounds into more subtle balanced ones more often associated with longer fermentation temperatures.

Seeing the results of a fermentation such as this one made me reflect on mine and the larger industry’s current tendency towards 2 week fermentations. While I cannot trace the exact history, I believe it has to do mostly from our English language. The home brewing movement in the States and Australia grew largely in part to a little help from our friends the British. While the rest of the world had conglomerated into a few light-lager breweries the English were experiencing a revival of its traditional styles. Books were written, research was getting done and the English reestablished a dying culture with their ESB’s and porters.

With our adoption of their techniques was an acceptance of their yeast and yeast care. Typical English yeast is highly flocculant and a low attenuator. Its like a shift-worker, gets in, gets work done and gets out as soon as it can. It leaves a spectacularly clear beer but also unfermented sugars and undesirable compounds such as diacetyl. With this yeast a fermentation past 5-7 days is useless. The yeast falls out of of suspension and declares its job is done.

Belgian yeast in contrast, behaves somewhat more similar to wild yeasts with a slower fermentation. In general, wild yeast consumes easily available sugars at similar rates to normal brewing yeast. However, wild yeast also contains an innate fight or flight tendency. Once the easy sugars are consumed the yeast does not fall out ready to die; instead, it pushes on less rapidly converting more complex sugars in attempts of self preservation. At the same time, these wild yeasts convert some of the harsh undesirable compounds into more subtle and complex flavours. This is not an exact science requiring a brewer to know their yeast and about proper barrel ageing; but, it’s a large part of the art of ageing and blending for sours and barrel aged beers.

While Belgian strains are not wild yeast by any means, I came to understand that they fall somewhere in between the extremes of English yeast and wild strains. Their characteristics bear resemblance to parts of both sides. When this struck me, I realised that I had certainly not given enough time to many of my fermentations. I had been demanding the yeast to work on my production timeline instead of allowing it to do its work in its time. All we can do as brewers really is create a happy, healthy environment for the yeast in the wort because the rest is simply not up to us.

It is often said that brewers make wort, yeast makes beer. It’s about time I start to believe it.




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