Sometimes I re-use yeast from one batch to go another round. This can be accomplished easily by simply brewing up a batch and pouring it into the fermenter on top of the trub from the last batch. This is not always practical as brewing is often a day-long event and we may only have time to rack or bottle on any given day. Washing yeast allows you to preserve it a clean environment for use at a later date.
After you have siphoned the bulk of your beer from the fermenter, you are left with some trub in the bottom. Trub is that lovely sludge of protein, yeast, hops and everything else that has settled out of your beer. It's the yeast that we want and not much of everything else that's gunked to the bottom of your fermenter. We want to isolate the yeast so we can store it. This process is known as Post Fermentation Yeast Washing.
Here's how I do it.
Start by making sure that you have the gear below (or reasonable facsimiles).
Sanitized or sterilized bottle with lid. Plastic ok.
Smaller bottle, preferably glass with metal screw cap.
Fig 1. Gear for Yeast Washing
Before you siphon:
Sanitize a bottle, cap and funnel. I use a plastic bottle of about 1 to 2 litres. I put it into a bleach solution along with the racking cane, hose etc. that I'll be using in the siphoning process. If you have a glass jar, boil it in water for 10 minutes to sanitize it. Leave it in the pot with water. Cover the pot and let it cool to room temperature.
Cover the fermenter when you have finished siphoning. This will reduce the chance of airborne infection; an eyelash or fly landing in the trub.
- Setup a clean workspace. Wipe down the surface with your sanitizing solution.
- Put the sanitized funnel into the sanitized bottle.
- Slosh the trub around and disturb the sediment to make it easy to pour.
- Using alcohol on a cotton ball, wipe the rim of the fermenter where the trub will pass when pouring.
- Carefully pour the sludge into the funnel/bottle. Leave a inch or more of airspace at the top of the bottle.
- Cap the bottle and place upright in the fridge.
The next day, you will see a separation similar to Fig 2.
Fig 2.Gravity Makes Layers
The yeast will be floating on top of the heavier sediments, but still suspended in the beer part. Rotate the bottle and you'll see the yeast swirling around at the bottom of the beer layer. See Fig 3.
Fig 3. Yeast in the Beer
- Boil and cover about 500ml of water.
- Sanitize another bottle. This one can be a little smaller. I use about 300ml size bottle.
(I use a glass bottle with metal cap and boil them with the water.)
- Place a normal drinking glass on your workspace, next to your sanitized bottle.
- Carefully pour off the beer layer into the drinking glass.
- As the beer layer gets down to near the sediment, gently swirl and switch to pouring into the sanitized bottle.
- Add some of the boiled/cooled water to the bottle and cap.
- Record on the cap; date, yeast strain and generation. E.g. April 21, 2007, Saflager, Gen 1.
- Place bottle upright in the fridge. If you can place the bottle way in the back of the fridge where it's very cool.
Fig 4. Ready
- Do not pour out too much of the sediment. We want a small amount of liquid with the yeast, but not too much heavy stuff.
- The boiled water must be below 40ºC (105ºF) or you risk killing the yeast.
- Boiled water contains little oxygen and extends the yeasts' life in the bottle.
- The idea of adding water is to dilute the alcohol exposure to the yeast.
The solution will separate into layers once again. You can wash again if you like, but I wouldn't bother. It's important to note that the more you handle the yeast and expose it to the outside world, the higher the risk of infection. I prefer to leave it as is until my next brew day.
How long will it keep?
If your sanitation practices are good you can store yeast in this manner for a month or more. I have kept washed yeast in the fridge, near freezing, for a month and a half and found nothing wrong with it. Some claim several months, but ultimately you will have to be the judge. Open the bottle and give it a sniff and let your nose decide. If it smells fresh and yeasty, then it's likely good to use. If is smells pungent, rotten, vinegary, sour or shows signs of other lifeforms, molds etc., toss it out.
Note that sometimes lager yeast strains give off a tiny amount of sulfur dioxide and may smell sulfury or like rotten eggs when you first open the bottle. This is acceptable and this should dissipate.
Yeast will slowly turn darker brown with age. People describe old yeast as peanut butter color. If it looks like peanut butter, toss it.
Always remember: It is not worth risking a good batch of beer and good ingredients on some bad yeast. Yeast is not expensive in the big picture.
How many times?
People often ask how many times they can wash and re-use the same yeast. The short answer is a maximum of five or six generations. Like everything else, there is a long answer too. Yeast are living, mutating organisms. Along with the yeast there will always be bacteria and other wild yeasts that co-exist in the trub. As time passes, the risk of making a bad batch of beer increases as other organisms compete with the yeast for resources. The actual number of generations will depend largely on your sanitation practices.
Before you brew
Take your bottle from the fridge and let is come back to room temperature. Give the bottle a gentle swirl to spin the yeast up off the trub and decant the liquid portion into your starter wort.
I hope that you have found this useful.