Yeast Wrangling: The Importance of Yeast

I recently purchased Pete Browns Miracle Brew book and a line in it reminded me I was to post about wrangling my own yeast. It was mentioned in the book that when the vast majority of people were asked about the ingredients of beer hops seemed to have been the number one reply with malt a distant second and water and yeast completely forgotten about.

Each of these four individual ingredients imparts their own unique flavor to the beer. But without yeast there is no beer.  Yvan De Baets from Brasserie De La Senne famously refers to his yeast strain as a ‘her’ and considers the yeast as part of the team such is its importance to his beers.

If you make a 40 litre batch of beer with malt, water and hops and split it into four 10 litre fermenters but add a saison yeast to one, a German Weiss yeast to another, a lager yeast to another and a pale ale yeast like US-05 to another you will end up with four different beers if controlled correctly. Saison, German Weissbier, lager and pale ale.

Yeast decides what your end result is so it amazes me that not enough people pay attention to this vital aspect of the brewing process.

A lot of people talk about a beer with a sense of place and will tell you about the beautiful barley that was grown in their own field and malted by their local maltster. They’ll tell you about the rows upon rows of hop bines growing a short distance from the barley and they’ll tell you all about the perfect-for-brewing well water taken from below the very field of barley. But then they go and buy a pack of the widely used US-05 to ferment it out with. The very essence of a beer and how it is transformed to its finished product is defined by your yeast so in my eyes the one main thing you should be harvesting from your own land, the one thing that will set your beers apart from everyone else, the one thing that nobody else will ever have is the wild yeast growing within your own environment and this is the side of brewing that excites me.

So how do we go about getting our own yeast? Well here’s how I do it and everything I have learned has come from a variety of sources such as Sui Generis blog, Milk The Funk and Bootleg Biology and all of these can give you a proper in-depth description with science included.

If I’m travelling abroad I bring small sterilised cotton swabs with me but I’ll focus on local yeast wrangling for now. First of all I decide on a beautiful location for a good long walk in the wilderness and luckily for me there are plenty of them in my locale with Newcastle Woods being my prime location. I then sterilise about five zip-lock bags and stick them in my pocket and head off for a stroll.


Eerie stuff. All I see is yeast.  

Then all you have to do is pick five random pieces of foliage and/or fruits off the beaten track and get them into the sterilised bag without touching them. I particularly like ones that have bees hovering on them.


Now you have five bags with leaves, berries, flowers etc. you will need five sterilized mason jars or beakers that can hold 250ml of wort.


Who doesn’t want to drink beer grown up from the foliage of an ancient ringfort in North Longford?  

Boil up 1.25 litres of dried malt extract. 1.25 litres of water mixed with 125 grams of DME and boil for 15 minutes aiming for 1.040 gravity. You can add some hops if you want to reduce the chance of growing lactobacillus and focus solely on Brettanomyces and saccharomyces. I also reduce the pH of this wort to 4.5 with phosphoric acid to eliminate the chance of growing bacteria. After the 15 minute boil it needs to be cooled to between 20 and 30 degrees C and now the wort goes into the sterilised jars with the foraged ingredients placed in each. Cover the whole lot and keep dark and in the 20c range for two weeks. Leave the lids slightly open to allow the Co2 to escape as it will explode your jar if it’s sealed tight.

Remove the berries/leaves etc if you can after a few days if they are not submerged in the wort as they will grow mould and infect the batch.


Russian Imperial Stout with wild berries kicking off a secondary wild fermentation.   

It is very important not to smell or taste the contents of the jar until the two week period has passed. After the two weeks I pull a sample from each jar and analyse it for pH, final gravity and aroma to decide whether or not it is worth proceeding with. Usually one in ten are worth keeping and stepping up with  500ml and 1 litre starters to see how they develop but at this stage we are checking to see if they first of all smell good and if alcohol has been produced. If it smells like a Monday morning poo after a Sunday drinking Guinne$$ then you have to discard it without even tasting it. If it smells of clove or banana or anything pleasant then you are on the right track so check to see if alcohol has been produced. Check the final gravity with your hydrometer and what I usually find with wild yeast is a fully dried out fermentation always lower than 1.005. If it smells good, your pH is below 4.5 and the wort has attenuated then leave it for a month before tasting it.


Four wild ferments on the go. First two possibly usable, second two are gonners! Check out the thin white layer of yeast on the bottom. 

If, after the month is up, you feel that it tastes like something you would like in your beer you can step it up using the same process as you would with normal liquid yeast and make a 500ml starter which is then decanted and the yeast added to a 1litre starter. You’ll have an idea of what beer you’ll get from it now so can decide on what style of beer you can produce or even use the yeast as co-pitch with something like a saison yeast strain for your own unique twist on a saison.

What I’ve found in a lot of my samples is an extreme spicy and prickly sensation on the tongue so even though they made it past all the tests of smell etc. they just still tasted bad and had to be dumped. It’s reckoned about 10% of your samples will result in something usable. I have a bank of lots of samples I consider good to use at the minute but am in the process of analyzing them on agar plates and through microscopes further to extract individual saccharomyces and hopefully Bretanomyces strains from the wild captures for the truly unique beer harvested directly from my local woods. Analysing your good sample further to see exactly what is in there is a post for another day along with naturally fermenting your wort under the night sky!

And this, folks, I consider a beer with a sense of place.

Thanks for reading.



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