A World of Yeast

When my brewing journey began over 15 years ago I would never have imagined the infinite number of flavour outcomes that could be achieved with 4 simple ingredients; water, barely / malt, hops and yeast. For plenty of years my focus was on the flavours produced by the barely and hops with little consideration of what yeast brings to the party. Many of us (me included!) get caught up with the hop derived flavours; the fruity, citrusy, herbal, spicy, you can see why you can get caught up just in hops alone! Remembering my first sip of a hazy New England IPA I was blown away by its hoppy intensity. But the yeast component of beer, in my opinion, is often overlooked but has a substantial effect on a beers final flavour.

In the long history of beer, yeast and its treatment in the brewery as we know it today is vastly different to the practices of the majority of beers history.

Prior to 1883 the understanding of yeast at a cellular level was limited and the majority of beers inadvertently contained a mixed culture of wild yeasts and bacteria described by Louis Pasteur as beer ‘impurities’. Pasteur identified various bacteria, wild yeast and moulds in production yeasts and developed a process of heat pasteurisation to eliminate the ‘contaminants’ in the final beer. But, by the stage of pasteurisation, these impurities in the production yeasts are likely to have impacted the flavour of the beer during the fermentation process.

Dr Emil Christian Hansen (one of the first directors of the Carlsberg Laboratory) built upon the work of Pasteur to develop the first pure yeast culture, Saccharomyces carlsbergensis. By isolating and culturing a yeast colony grown from a single cell, Hansen was able to create a pure yeast culture for use in the Carlsberg brewery. You might ask why this was important, well with a pure culture you are able to more accurately determine the characteristics of certain yeast including its flavour contributions, attenuation (the extent to which it converts sugars into alcohol), tolerance to alcohol and flocculation behaviours (how the solids within the beer clump and fall out of suspension to create sediment and produce a clearer beer).

The work of Hansen revolutionised the way in which brewing was carried out and over the subsequent years various labs have isolated vast numbers of pure yeast cultures which are used in brewing both commercially and at home today. You only need to look on the White Labs website to see the huge variety of commercially available pure cultures you can get your hands on.

Wild yeast captures in Erlenmyer Flasks

Above: A selection of Wild Yeast captures being propogated which make up part of our house culture

It wasn’t until I begun to take the craft more seriously that I started to take notice of huge variation in flavours that’s can be produced from simply changing the yeast. Until that time the focus of the yeast for me was purely on how they turn the sugars into alcohol with very little thought in the other compounds yeast produce during fermentation. This began my exploration into different commercially available yeast strains whilst homebrewing but this was just the beginning of what is really out there in a world full of yeast…

Around the same time I had been dabbling with sourdough and when you think about it, beer is really just watery bread! I am obviously over simplifying it but the processes are so similar, with almost identical starting materials combined with the biological process of fermentation. With this at the front of my mind I headed off down the rabbit hole of spontaneous and mixed fermentation beers.

At Castle Brewery I still use pure cultures of yeast to produce our range of “clean” beers. These are mainly the classic range of beers produced at the brewery where I am looking for a high degree of repeatability and consistency between batches typically fermented over a known length of time. But the alure of mixed cultures and wild yeast have really sparked an interest in the possibilities of creating something truly unique here at the brewery.

I have spent the last 2 years capturing and cultivating wild yeast and bacteria from right here in Cornwall, developing a house culture which I aim to begin using at the brewery. I won’t go into the process in this post but rest assured there is one coming! For now all I will say is I currently have an understairs cupboard full of wild captures along with various bubbling demi-johns dotted around the house, much to the despair of my ever supportive partner Sarah.

The flavours of these various captures range anywhere between the classic horse blanket bretty flavours to a lactic producing bacteria giving off something that can only be described as apple juice! It is all really exciting and I am just itching to get started on producing some great wild and mixed fermentation beers.

Each “wild” beer that will be produced will be limited run batches, each completely unique and one of a kind. The house culture will be ever developing with additional wild yeast and bacteria captures being added throughout the year. The “wild” beers will be untamed and wild by nature. Over time a mixed culture tends to naturally drift as the microorganisms outcompete each other, rather than trying to contain and control this I will be working with the natural processes.

So, watch this space, there are some really exciting and wild things to come very soon…

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