If you’re a homebrewer or a home baker, you may have looked at an empty bottle of beer and noticed a layer of yeast in the bottom of the bottle, and wondered if it’s possible to use that yeast for your own brewing or baking. The simple answer is yes. However, it can require a little time to do, as the yeast needs to be built up slowly. So let’s find out how to get yeast from beer.
Which beer can I use?
To be clear, not all beer will have yeast in it. The beer will have been fermented by yeast, however, many commercial brewing companies will filter their product, in order to provide the customer with the clearest beer possible. This filtering process will clear virtually all the yeast cells from the liquid, rendering it useless for trying to propagate yeast from it.
‘Craft’ brewers will generally not filter, and it is these beers we can use.
The next caveat is that the yeast used to ferment the beer, may not be the same as the sediment you find in the bottom, as brewers sometimes use different yeast to carbonate their beer, from the yeast they originally fermented with. Your beer may therefore not taste the same as the beer you drank. Also, if you are using the yeast for baking, the flavour may not be what you thought. It will still make beer or bread though, so it becomes an interesting experiment.
Waking the yeast
We need to make a basic weak beer. This will give the yeast food and nutrients to bring itself out of dormancy, and to start producing new yeast cells. In order to do this, we need Dried Malt Extract (DME). Liquid malt extract is obviously fine, however the dried version is much easier to store and use small amounts.
It is also possible to do this with table sugar, however, there needs to be nutrients for the yeast to consume. If there is a large amount of yeast in the bottle, then there are possibly enough dead yeast cells, which will provide the necessary nitrates for the yeast. I can’t promise how successful this sugar method will be each time, but you lose nothing by trying. If you are propagating this for bread yeast, then sugar will PROBABLY work for the first step up at least.
Making our starter beer
To make our ‘beer’, the rule of thumb is to add DME to water at a rate of 10% by weight DME to water weight. So, for our first step I am going to use 5 grams of DME to 50 ml (grams) of water. I am using this amount as I have quite a bit of yeast left in my bottle. If there is barely a smear of yeast in the bottle, then start even smaller. More like 2.5 grams and 25 ml.
The important thing is to start small. Brewing yeast is quite an aggressive ‘fungus’, and will usually dominate over most others. However it can only do this if it is in high concentration. If we give it too much food at this stage, then the yeast will not be able to reproduce quickly enough to dominate. That might allow another bacteria may take hold.
Add the water. Use a small pot at this stage so as to not evaporate away all our liquid.
Now place the pot on the stove and bring the liquid to the boil. This barely needs any time boiling. All we are trying to achieve is sanitising the ‘wort’. If we boil it for any length of time the water will evaporate and the wort will be too strong.
Once our sanitising boil is complete, the wort must be cooled. Pouring hot wort onto the yeast will kill it, and all we’ll get is dead yeast from beer. Ideally, we want to get this cooled to below 20°c (68°f). The easiest way to cool, is by sitting the saucepan in a bowl of water. If you are going to leave the wort for any length of time, put a lid on it to keep out any wild yeasts.
Sanitation
Every item we use from now on must be be sanitised. I’m using a no rinse sanitiser, which is in the bowl in the below picture. The most common brewing brand for this is StarSan, but there are different types. If you don’t have sanitiser, then perhaps boil the items to sterilise them.
The wort is now poured into the bottle of yeast dregs.
Cover the bottle top with some plastic wrap. We are not trying to seal the bottle. Instead, we just want to stop anything (dust) from falling in. The fermenting wort will create carbon dioxide, so do not put a lid on it, or it may explode.
Aeration
The yeast need oxygen to reproduce. To provide this, we are going to shake the bottle for a minute or so. This will aerate the wort sufficiently. I advise giving this a light swirl everytime you pass by from now on. That will help aerate and rouse the yeast to keep it in suspension.
Place the bottle somewhere warm, preferably around 20°c (68°f). If it’s too cold, the yeast will stay dormant, and if it’s too hot, the yeast may die.
Keep it out of sunlight and leave it for 24/48 hours, swirling occasionally.
After 24/48 hours, you should have something similar to the picture below. You can see areas of more dense white bubbles forming. Also, there is some white yeast starting to form at the bottom. This is ready for the second step up in size
Stepping up the volume
As I said earlier, we need to start small, so as to not overload the yeast with food. This applies to each step up as well. As a rule, don’t go any larger than ten to one as the largest step, and it’s a good idea to be slower than that when trying to propagate yeast from beer bottles, especially in the early stages. So, as we started with 50ml on the first step, I’m going to step this up by four. Which means, we now need to make 200ml of wort.
The same rules apply, and we follow the steps from above. This time, will now need 20 grams of DME and 200ml of water. Boil and cool as before.
If you are not using DME, and your first step was with some sugar, then it is possible to use a very thin flour and water mix here. Obviously it can’t be too thick, else it won’t pour and aerate. It’s difficult to boil a flour and water mix. It is possible, but must be mixed well whilst cold. Boil this mix breifly and possibly thin again post boil.This will sanitise the flour, and ensure you don’t get a wild yeast, and end up with sourdough.
Once again, sanitise your funnel, and pour the cooled wort into the bottle.
Put the plastic wrap over the top again, and give it a good shake to aerate the wort. The yeast need a lot of oxygen to grow and reproduce, so the more often you can give this a swirl through the day, the better. As brewers, when we make a yeast starter, we use a swirl plate. This swirl plate continuously forms a small whirlpool, and continually aerates the wort. So, to get healthy yeast from beer, swirl as often as you can remember.
The result: Yeast From Beer
After another 24 to 48 hours, you should see signs of fermentation as below. There is a good layer of foam on the top, and there are bubbles running up the sides.
You can see the healthy white yeast forming on the bottom of the bottle. In a flour water mix, all you’ll see are bubbles on the surface, if you’re lucky.
This is as far as I take it in the bottle. After this, I make a large version of the wort mix (a starter) and pour the whole bottle contents in to that.
When we have used this for bread, I also pour the entire contents into a dough mix, and treat it like a sourdough starter from here.
If you’ve made it to the end here, then thanks for reading. I hope it has given you some help and a few ideas.
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