How to Harvest and Culture Commercial Yeast for Homebrewers

Beer does not make itself properly by itself. It takes an element of mystery and of things that no one can understand. – Fritz Maytag, Anchor Brewing Co.

As a homebrewer, I remember first learning just how critical yeast is to homebrewing—sometimes the hard way. More than any other fermented beverage, beer depends on yeast for flavor and aroma. Sure, hops, grain and water are all important, but it’s yeast that can really make or break your beer.

There is no doubt homebrewers have access to lots of yeast strains, but sometimes a particular strain isn’t available. We’re here to show you that it may be possible to culture your desired yeast from a bottle-conditioned beer.

Most commercial beers are filtered, but some brewers will bottle-condition their beers and it’s usually advertised on the label. You can also look to see if there is a layer of sediment on the bottom of the bottle (this is the yeast).

Before culturing commercial yeast, you need to know the condition of the yeast you’re trying to culture. Fresh beer that has been stored cold and is not extremely alcoholic will have a good shot at recovery. Yeast stressed from heat, age and/or high alcohol levels will be much harder to salvage.

So without further adieu, here are the steps to harvesting bottle dregs.

Harvesting and Culturing Yeast

  1. Take your sanitation seriously. Sanitation is extremely crucial in this process. The number of viable yeast cells in a bottle is probably low and any contaminating microorganisms that mix in with your culture may grow faster than your yeast, making everything you’re doing useless. Make sure everything you use and touch in this process is well sanitized.
  2. Gathering the yeast. Wipe down your bottle with 70% ethanol solution or isopropanol. Pour off the beer slowly, leaving behind the sediment at the bottom. Let the alcohol evaporate then sanitize the top of the bottle to kill any microorganisms that were hiding underneath the cap. Cover the top of the bottle with sanitized aluminum foil and let the bottle warm to room temperature.
  3. Wake up the yeast. You’ll want to create a small amount of wort (specific gravity between 1.015 – 1.020) using DME to cover the bottom of the bottle (2-3 mL). You want to feed your yeast a manageable amount of wort. Giving too many carbohydrates, oxygen and other nutrients can stress your yeast.
  4. Pour the wort down the side of the bottle so as to not disturb the yeast. Add a small pinch of yeast nutrient. Sanitize the top of the bottle again and cover it with the sanitized aluminum foil.
  5. Let it sit and incubate for no more than three days at 70-90°F (21-32°C). A good place to do this is on top of a refrigerator that provides a little warmer climate. Make sure to keep it out of direct sunlight.
  6. When stepping up healthy yeast cultures, a good rule of thumb is to pitch the yeast culture to a wort 5-10 times the volume of the culture. Earlier step up stages stick with five times the amount so you don’t stress the yeast. Limiting the amount of wort you add also helps prevents unwanted microorganisms from culturing.
  7. Once three days have passed, transfer the fermenting wort to a small culture of fresh wort (about 15 ml, which is five times as much liquid as you have now). Before transferring, sanitize the tip of the bottle and pour the yeast sample into the new container. Make sure whatever container you use is properly sanitized and preferably sterile. You can add a pinch of lysozyme—an enzyme that kills lactic acid bacteria and is available at most home winemaking shops. This gives your yeast just a little more protection than it otherwise had before.
  8. Cap immediately and incubate at 70-90°F (21-32°C) for no more than three days.
  9. You should see signs of fermentation, such as foam on top of the wort, cloudiness in the wort or just a layer of yeast at the bottom. This is fantastic! You’re (nearly) home free!
  10. Now that your yeast is healthy, perform another step up at 10 times. In other words, from 15 mL you’re going to create a culture of 150 mL. Use a higher OG wort to improve culturing (1.030 – 1.035), aerate well and add a pinch of yeast nutrient. Incubate for no more than three days at 70-90°F (21-32°C).
  11. The 150 mL culture should ferment like a little batch of beer. When it’s finished fermenting, the resulting liquid should taste like beer. As a test, transfer some of the liquid into a sanitized container and refrigerate overnight so the yeast settles. If it tastes good, then proceed with the process.
  12. Follow step 10 again, doing another 10 times step up, to get 1.5 L.
  13. Once the 1.5 L yeast starter shows activity, it is ready to pitch to your homebrew. If you want to be cautious, you can let it ferment out, do a second tasting similar to step 11 before using it.

There are other methods to culture yeast from bottle-conditioned commercial beers, and if those work for you then by all means stick with your proven method. The above method is a cautious, meticulous approach to ensure you don’t stress the yeast and end up with a high success rate.

Which ever method you choose, know the yeast is strong with you.

 


Sources

Homebrewers Association
Homebrewers Association