Whether you're brewing beer, cider or wine, yeast is one of the most expensive home brewing ingredients. In combination with another strategy--brewing a yeast starter from one vial of yeast instead of pitching multiple vials--harvesting yeast can save you money and ensure you always have viable yeast ready to pitch at short notice.
This article assumes you're a typical homebrewer using starter brew kit equipment to brew with. If you're brewing at a larger scale, there's a pretty good chance you already know how to harvest yeast...
- Fermenter (glass or plastic)
- Sanitizer (e.g., Star San) solution in spray bottle
- Mason Jars with lids
- Canning tongs
- Oven mitt
Yeast can be harvested from a primary or secondary fermenter (if you use one). After you siphon your beer from the fermenter, leaving the trub behind, you'll be adding sanitized water to the trub, swirling it up, and then transferring the resulting liquid to sanitized jars, where you'll let it settle out before transferring the lighter top layer--which contains the yeast, to other sanitized jars. These last jars will be refrigerated up to a few months and can be used to create a yeast starter to pitch on a subsequent batch of beer.
Preparation (once fermentation is complete):
- Sanitize three times as many jars as you'll need to contain yeast (i.e., start with 6 jars, end up with 2) in boiling water by boiling both the lids and jars, submerged, for about 20 minutes.
- Remove the jars and lids with tongs; fill the jars with boiling water, set aside to dry and cool (oven mits and tongs are handy here)
- Siphon your beer/cider/wine to its destination (another fermenter, a keg, a bottling bucket) per normal sanitary practices
- When the jars are cool, pour the water from the jars into the trub
- Swirl the water/trub until it is a suspension
- Transfer the solution into 4 of the 6 jars, leaving the others empty
- Sanitize the lids with sprayed sanitizer solution and seal the 4 jars
- Allow the yeast/trub to separate--the yeast will be suspended in a translucent layer in the top--takes about an hour
- Pour off the top (yeast) portions of two of the yeast-containing jars into one of the empty jars; repeat the process with the remaining jars
- Sanitize and seal the 2 jars you've poured yeast solution into
- This will settle out again, but the trub portion should be small enough at this point not to matter
- Refrigerate your yeast--it will last up to a few months. Plan accordingly.
Using Your Harvested Yeast
When it comes time to use your yeast, you'll need to create a yeast starter to revitalize it prior to pitching, as this yeast is more dormant than when you get a new vial of it.
A starter consists of the contents of your harvested yeast jar, warmed to room temperature, which are then mixed with a small amount of sanitized 'yeast food' (for beer, this could consist of half a cup of extract boiled in a pint of water and then cooled to room temperature) and then set aside for 24-48 hours in a sterile container before pitching to a new batch. Proper sterilization is important with starters--treat them as you would your normal fermentation.
Note: Yeast mutates quickly, so you can't harvest yeast from the same initial strain indefinitely before its character will begin to change. You should, however, be able to re-harvest half a dozen times or more without major shifts.