Brewers always look for ways to stretch their resources to cut costs. One of the techniques used by both small and commercial breweries is to reuse their brewing yeast with successive batches.
Industry experts suggest that brewing yeast can be reused 5-6 times, but no more than 10. There are several options for harvesting yeast, but it will generally be taken either from the top or the bottom; no matter the method you choose, you must avoid contamination to ensure a consistent flavor. If there is any doubt, don’t use the harvested yeast.
Read on to find out how to harvest and reuse yeast properly and what to watch out for.
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How many times can brewing yeast be reused after the first batch?
Under perfect conditions, brewer’s yeast can be reused indefinitely from batch to batch. But the reality is that conditions can change each time you harvest yeast for the next brewing cycle.
Even if the changes are minor, they stack up (called drift) to the point where the beer won’t be the same as the first batch.
The consensus is to only reuse the yeast for 5-6 batches and no more than 10.
The further the yeast develops and evolves from the original, the bigger variance you’ll see from the original beer. This may not be a problem for you if you’re brewing as a weekend hobby, but a lack of consistency can become a major issue as you increase your production size.
How do you reuse yeast after the first batch of beer?
The process of reusing yeast is called yeast harvesting. According to homebrewsupply.com, harvesting is when you create a new culture from the previous batch to use it for the next one.
The folks at Wyeastlab also recommend that only certain types of yeast should be harvested.
To harvest yeast, you should:
- Select the youngest generation to minimize mutation.
- Harvest from a low gravity and low hopped beer as this yeast undergoes the least amount of stress during fermentation.
- Only harvest yeast that exhibits normal fermentation characteristics.
You should have enough experience with the home brewing process to recognize the normal characteristics of your yeast, including how it smells.
Key Point #1: When in doubt, don’t use the harvested yeast.
Brewing beer is more art than science, so the exact methods of harvesting yeast can vary on the type of beer.
If you have any concerns about the quality of the yeast, err on the side of caution and don’t use it. You’re better off losing a round of yeast than a whole batch of beer.
Yeast harvested from a beer that wasn’t quite right has been exposed to unsterilized containers, or just plain seems off should be dumped.
Key point # 2: Sterilize everything!
Contaminated yeast can easily cause changes in the expected characteristics of your next batch. If the beer has a different color or aroma, the yeast was likely contaminated.
Regardless of the method, sterilization of all implements, containers, and anything else that might contact the yeast is necessary.
This includes the water used in the washing process, which is brought to a boil and allowed to cool before use. Distilled water can also be used.
What is yeast washing?
Yeast washing is the process of reclaiming the yeast typically found at the bottom of the fermentation container.
The containers are decanted repeatedly (washed) until the layer of yeast is mostly isolated and stored for later use.
Is it possible to reuse yeast without washing?
It is possible to reuse yeast without washing. This method is called top cropping.
Top cropping is when you open the fermentation container while the yeast is actively metabolizing sugars into alcohol.
Take care when doing this, as it will add oxygen to the environment and alter the batch.
How do you harvest yeast?
The easiest method of harvesting yeast is top cropping.
Within the fermentation container, the youngest (and most active) yeast is along the top, while the older (inactive) yeast sinks towards the bottom. This activity creates a foamy layer called krausen on top of the liquid.
To harvest the krausen, simply take a sterile stainless steel spoon and scoop it into a mason jar or other container. Be very careful to make sure the spoon doesn’t touch any surface that wasn’t sterilized while transferring between containers.
Since top cropped yeast isn’t washed, it can go straight into a container with sterile or distilled water and into refrigerated storage. Leave room at the top and keep the lids loose.
Reusing yeast slurry (bottom cropping)
Bottom cropping is basically the opposite of top cropping, meaning that you will be pulling the yeast from the bottom of the fermentation container rather than the top.
To bottom crop your yeast:
- Start with the slurry at the bottom of the fermentation container. This slurry is a mixture of beer, solid compounds left over from the fermentation process (trub), and yeast.
- Add sterilized or distilled water to the container and mix or swish to pick up solids at the bottom. You want to suspend everything in a mixture before pouring it into another container large enough to hold it all.
- Let this mixture sit for at least 30 minutes to develop two different layers. Most of the solids will sink to the bottom followed by a layer of liquid above it. The yeast will be suspended in the liquid.
- Pour the liquid into another sterile container and discard the solids. Let this container sit for another 15 to 20 minutes. The liquid should settle into two distinct bands. There should be a lighter layer of liquid above a darker one. Don’t worry if you can’t see two layers. Just keep in mind that the yeast is suspended in the upper part of the liquid.
- This top layer can be poured into your final storage containers. If you are using mason jars, make sure the lids are sterile.
- Screw the lids until they are just about snug and then back them off slightly.
Key point #3: Don’t over-tighten the lids!
There might still be a little bit of active fermentation, which will produce gas. You want the lids to allow the gas to escape.
Place the final containers inside the fridge. After 24 hours, you should see a light band of yeast at the very bottom.
For a video of the process (with some cool time-lapse segments), check out this clip from Clawhammer Supply:
Reusing yeast cake
If yeast washing sounds like too much of a hassle, you may want to consider skipping it altogether and just reuse the yeast cake.
This is still bottom cropping, so you’ll need to start with an emptied fermentation container. You’ll want to pour out most of the slurry at the bottom until you are left with mostly the solids.
That solid layer is called the yeast cake. To reuse, simply start the next batch right on top of this layer.
This will mean that you need to be ready to start your next batch right away. You won’t be able to store yeast cake because the yeast is still active, but now they don’t have a food source.
Can you harvest yeast from commercial beer?
If you’re just getting started, you might be considering starting from a beer you bought and enjoyed.
It is possible to harvest yeast from commercial beer, but only if the beer is unfiltered. The filtration process will have strained the yeast out of the beer before bottling.
To harvest yeast from a bottle of commercial beer:
- Start by letting the bottle sit in the fridge undisturbed for at least 24 hours. You want the yeast to settle to the bottom so the longer it sits this way, the more yeast you’ll be able to harvest. A few days would be ideal.
- Next, open the beer and sanitize the lip of the bottle. A simple alcohol swab should do the trick.
- Make a continuous pour until you have about a 1/4 of the beer left. The majority of the yeast should be in this last portion of the bottle.
Homebrew Supply suggests using this beer to create a small starter batch of yeast. They list their process to create larger subsequent batches until you have enough to store.