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We talk about mixed fermentation a lot at Yonder. If you follow us on social media or have ever been to one of our tasting events, you’ll have heard all about our ‘house cultures’ and ‘funky farmhouse flavours’. Increasingly, though, we’re realising not everyone knows what we mean by those terms.
As a self-proclaimed modern farmhouse brewery, we try to get as many ingredients as we can from the area around the brewery. That means we do lots of foraging and working with local farms, but that definition also stretches to our use of barrels and production of sour beer using mixed fermentation. These methods have rich histories in the roots of brewing, and many well-known beer styles today have only been revived with the rise of creative fermentation.
Mankind has been through the phase of wanting to monitor and control everything, and there’s a new trend for trying to keep things natural, to take our time and follow nature. That’s really evident in the brewing world. What better way to get your geek on than by studying the real heroes of brewing – yeast (and bacteria!).
So, what is mixed fermentation? If you think you know already, try not to skip forward to the why because you might miss out on some debate. Being such a loose term, mixed fermentation – or mixed ferm – is open to interpretation.
Before I get stuck into opinion, here are a few facts. Yeasts are fungi, tiny, microscopic, single-cell fungi. Fungi is a kingdom. Not a species or a genus – a kingdom. It is neither plant nor animal. That’s pretty top level, basic stuff. But we didn’t even know about yeast until relatively recently.
It wasn’t until the 19th century that Louis Pasteur discovered and began to understand the fermentation process. This took the production of beer from the realm of religion and superstition into the world of science. Ever since that time we’ve been on a mission to control and manipulate these tiny organisms to get the best results – the highest alcohol, the best flavour and, of course, consistent results.  We’ve got pretty damn good at it, too! The modern lager and its yeast, Saccharomyces Pastorianus, are a testament to the innovations of brewing science (that’s a blog post in itself).
 When people talk about yeast it’s usually a general term to reference a certain species: Saccharomyces Cerevisiae. This is the species that mankind has cultivated over the years for baking and brewing. Now, let’s think about this strain as a domesticated dog. Think about how many variations of the domesticated dog there are, all with their own characteristics. Our brewery dog is Taco, a Jack Russell. He was bred to get in small places and catch rodents. But a husky was bred to pull sleds in the snow, a Chihuahua to...go in a handbag?
However different they all are, they are still the same species. Canis Lupus Familiaris. Mutations of the grey wolf. It’s exactly the same with Saccharomyces Cerevisiae. Within that one species you have multitudes of variations that in yeast we call strains. There’s Wine and cider yeast, trained to enhance fruitiness of the grapes/apples; ale yeast with thousands many flavour and performance variations, within this title alone; and bakers yeast, which has a much stronger focus on the CO2 production to leaven the dough.
 Standard brewers yeast isn’t alone in its ability to create alcohol and CO2 though. There are many families of ‘yeast’ which exist solely to consume sugar and multiply.
So that I don’t go too far into the rabbit-hole here let’s focus on just one of these genera: Brettanomyces.
Brettanomyces or “Brett” in brewing is often referred to as a wild yeast and, while its roots are most definitely from spontaneous fermentation, many of the beers you’ll see produced with Brett use strains that have been isolated and grown in a lab, much like standard brewer’s yeast. In the world of wine and in most brewing, brett is a curse word – an “infection” can cause a lot of damage to a product due to the off-flavours that it can create during fermentation. Some of these flavours can be described as medicinal, farmyard or even smokey. So, the emphasis in production is to avoid the risk of cross contamination. 
It hasn’t always been this way. “Natural wines”, where the winemaker intervenes with the process as little as possible, are a good representation of what wine probably used to taste like. It’s like a delicious history lesson in a glass, but it’s also becoming very popular.
 Orval, the Belgian beer classic famous for its bretty finish, initially contained this yeast naturally, almost by accident. The story goes that during a brewery upgrade, equipment was replaced (or cleaning processes were improved) and the beer produced just didn’t have the depth; it had lost its soul. People could tell the difference and they didn’t like it. The brewers decided to give the people what they want. They had to go back to mixed fermentation.
 So, there we are. I’m nearly at my point. Orval is one example of a mixed fermentation beer. Brewed with standard brewers yeast (Saccharomyces) but also with the addition of (whether intentionally or not) Brettanomyces. 
So here’s where the opinion kicks in. Brettanomyces and Saccharomyces are two different families of organisms, not different strains. It’s like a Shepherd and a Sheep Dog, working together to herd sheep. Or Carole Baskin, getting her Tigers and Lions to help dispose of her husband. Two different taxonomic orders working together to get results.
It’s not two people working together in a factory. Even if they are a different colour or creed, or doing a different job, they’re still both human. That’s mixed culture and it’s a good thing, but it’s not mixed fermentation. Don’t put a wine yeast and an ale yeast together and call it mixed fermentation, because it’s misleading.
Hey, did I mention bacteria yet? I won’t got too far into the taxonomy of bacteria, mainly because I don’t think I’ll beat the domestic dog reference. However, I do want to say that, as far as mixed fermentation beer goes at Yonder, bacteria are the key. We are talking, specifically, about lactic acid bacteria: Lactobacillus (also used in the production of yoghurt) and Pediococcus (also used in food fermentation, such as charcuterie). In simple terms, the yeasts ferment the sugars in the wort and convert them to alcohol (and CO2), while the bacteria creates the acidity. In reality, there is so much more going on beneath the surface.
For example, some strains of yeast create acids in the right circumstances;
some types of bacteria are inhibited by alcohol or by hops; Brettanomyces is the only organism in our cultures that can break down the gloopy by-product of Pediococcus. Each and every cell in that liquid is fighting for something, mainly to feed and reproduce, but in doing so they end up helping each other. The interplay of all these processes, ultimately, helping us by making something delicious.
To make my point about mixed fermentation above, I asked my daughters to give me some examples of humans and animals working together. My eldest, Isobel, suggested using the relationship between plants and pollinators and what humans and other animals get from their cooperation. It was so good that it’s now how I’ll always think of our mixed cultures. 
You see, if you take just one of those components away, you’re left with nothing. If our cultures were just Brettanomyces, the beer would probably be thin and very dry; if you had Pediococcus and no Brett, the beer would go thick and never recover.
The balance between the two is serendipitous.
With all of this going on in our beer, it takes much longer between grain and glass than a single isolated strain of yeast would take. We’ve got to wait months for fermentation to finish completely, sometimes years. Then we have to re-ferment our beers in the bottle and condition them for months before they’re ready to go out into the wild.
 When it’s put like this, it’s difficult to understand what the benefits are. We could just make single strain ales, we could quick sour with lacto cultures, we could force carbonate. But all of those would result in one key issue – less complexity, less variation, less invention. I promised at the start of this rant to explain why we focus on mixed fermentation at Yonder. We’ve caught the bug for bugs and there’s no going back. If you skipped to the why – maybe it’s best to skip back a bit.

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