To perform well, yeast must be allowed to respire, consume and reproduce. If yeast is to do all that we demand, certain care must be taken, especially during storage. This 5-step regimen removes waste products, kills bacteria and ensures healthy, robust yeast. You will be rewarded with more consistent fermentation, better-tasting beer, and a greater number of generations from your slurries.
Harvest Yeast Immediately after Final Gravity has been Reached, before Diacetyl Rest.
Even if it is kept very cold, yeast should not be stored on the cone or under beer. To yeast, beer is a nutrient-poor waste product, and forcing it to reside there may cause the viability to drop precipitously (over 50% within 48 hours), no matter how cold it is kept!
Sterilize valves with 70% alcohol and flame, and sanitize any hoses, utensils and storage containers to be used. Catch the MIDDLE LAYER of yeast in a storage container as follows, discarding top and bottom layers:
- CONICAL vessels require draining the bottom trub-filled layer until good color and consistency is seen.
- ROUND vessels require manual harvesting with a paddle (layers mix if allowed to drain through the valve). Thoroughly degas yeast by shaking storage container and allowing gas to escape through lid.
Clean the Slurry.
Contamination often occurs during transferring and handling, so it is wise to treat the yeast once it has been harvested and safely contained. Do not use the standard acid-wash, for it often leaves live bacteria behind and lowers yeast viability. Use the chlorine dioxide method given below, which has proven to be both extremely effective on all types of brewing bacteria and yet gentle enough on brewing yeast to use every harvest (see Sep/Oct ’98 issue of The New Brewer for details).
- For every gallon of yeast, acidify about 100ml of water with a pinch or splash of citric or lactic acid.
- For every gallon of yeast, add 2ml* chlorine dioxide to the acidified water. When concoction turns a light yellow (may take a minute), add to the yeast slurry, mixing well.
- Allow to sit for a minimum of 30 minutes (longer reaction time ensures effectiveness) before using. *Available from BIRKO as DioxyChlor™ at (800) 525-0476 and Five Star as Star-Xene™ at (800) 782-7019.
Store at 34°F/1°C.
Washed and fed yeast will retain high viability for 2 weeks at this temperature. Warmer temperatures will decrease storage times. If your cold room maintains temperatures higher than 34°F/1°C, you must either place the yeast storage container in an ice bath in the cold room (which maintains an ideal temperature if ice is present), or you must feed the yeast more often. If storage times of more than 2 weeks are desired, drain old wort off the yeast bed and replace with fresh wort every 2 weeks.
Test Your Slurry before Pitching.
Don’t brew blind-folded! Check viability, cell count and purity. See our Brewers’ Laboratory Handbook for easy-to-follow procedures. Use our free online Pitching Rate Calculator.
Clean and Feed Your Yeast.
Why hose that perfectly good yeast down the drain just because the next brew day is too far out? This unique product allows you to prepare yeast for a week of storage in 30 minutes flat.
Using pre-measured quantities of sterile cleaning and feeding solutions, this simple, 2-step process allows you to “clean” the slurry with activated chlorine dioxide to kill any bacteria present, and to “feed” the yeast with sterile, concentrated wort. Then, simply store the slurry at 34°F/1°C, until needed, for up to 2 weeks. Treatment can be repeated innumerably.