Washing yeast is a sensible practice for most homebrewers. Yeast is one of the most important ingredients in beer and can be quite expensive.
If you have to buy a new packet or vial of yeast for every batch of beer, it can quickly add up. One way to reduce costs is by reusing yeast. If there isn’t much trub (sediment) in your fermenter, you can pitch another batch of wort directly onto the yeast cake immediately after transferring to the secondary fermenter or keg. Some brewers don’t have any issues with off flavors when reusing yeast.
Harvesting and Washing Yeast from a Conical Fermenter
There will always be some trub at the bottom of every fermentation vessel. If you use a conical fermenter, removing trub is easy.
Layers of Yeast Defined:
Open the bottom valve and drain the trub before the yeast begins to flocculate (settle). Discard the bottom portion of the flocculated yeast since it contains a high percentage of yeast that settles quickly and attenuates poorly. The middle layer of yeast is what you want to harvest. It should be creamy in color and texture, free from trub, and have no off odors or tastes. (Yes, some people do taste yeast.)
Discard the top layer of yeast because the yeast in that area settles the least. You want to harvest the “average” yeast in the middle. This “average” yeast will consistently produce reliable results that can be predicted. If you harvest yeast from the top or bottom extremes and propagate it, you will change the properties of your yeast, making it difficult to predict its behavior.
Harvesting Yeast From the Bottom
The principles of harvesting yeast from a conical fermenter also apply to harvesting yeast from the bottom of your primary fermenter. Again, you want to obtain the “average” yeast. Since you’re harvesting from the primary fermenter and not the secondary, you will favor the most flocculant yeast.
You won’t be as precise as with a conical fermenter, but you should still be able to get the desired yeast. As mentioned before, there will be a lot of trub at the bottom of the primary fermenter, consisting of hot and cold break material that made it into the fermenter. To harvest the cleanest yeast possible, we’ll use yeast washing techniques.
Homebrewers’ yeast washing methods should not be confused with what commercial breweries do when they “wash” their yeast. Commercial breweries lower the pH to just above 2.5, which kills off most unwanted bacteria. However, since wild yeast is still yeast, you can’t remove them by washing.
For the average homebrewer, it’s simpler to buy another packet of yeast than to risk damaging your yeast by adjusting the pH using acids.
Yeast Washing Procedure:
For the rest of us, yeast washing involves adding sterilized water to a mixture of yeast and trub, chilling the mixture, separating the yeast from the trub, and repeating if necessary. This is one of those situations where meticulous sanitization is crucial.
The steps involved in yeast washing are as follows:
Immediately after racking beer off the yeast, add a pint of sterilized water to the bottom of the fermenter and swirl to loosen and suspend the yeast.
To sterilize the water, sanitize quart or pint jars and lids (similar to canning) by boiling them in a separate container while the water is boiling. Boil the water for 15 minutes, add it to the jar, leaving about 1/2″ of headspace, quickly seal the jar with a lid, and let it cool before using it to wash your yeast.
Wait a minute or two to allow the heaviest trub to settle, then pour off the mixture from the trub (this can be challenging) into one of your sterilized mason jars.
Cover the jar with foil or cling wrap, secure it with a rubber band, place it in the refrigerator, and wait for it to settle. This may take 30 minutes to an hour.
You should see three layers: suspended yeast on top (along with any remaining beer), a fine layer of yeast below that, and trub at the bottom. Pour off the beer if necessary, then transfer the liquid with the suspended yeast to a second mason jar, discard the trub, and clean and sanitize the first jar with Iodophor.
Cover the second mason jar and refrigerate it to allow further settling.
If you notice a significant amount of trub at the bottom of the second jar, repeat the above process. Eventually, you’ll be left with several inches of clean and creamy yeast.
Once you’re satisfied with your washed yeast, make sure it’s well-covered and store it in the refrigerator. Ideally, it should be stored at 33-34°F (0.5-1°C). It’s “supposed” to last a couple of months, but it’s best to use it as quickly as possible.
When you’re ready to use the yeast, stir it back into suspension and pitch it into an appropriately sized starter the day before you plan to brew.