First, my apologies for such a basic question, but in my research I have noticed that some people suggest reusing yeast by pitching wort over the existing trub/yeast in a primary fermenter immediately after racking the beer that had been on it into a secondary fermenter, or by harvesting some of that yeast to use with the new batch of wort. Other people, including Wyeast and/or White Labs and John Palmer provide information for washing yeast when taken from the primary fermenter before repitching it.

Or, if timing is right, it is preferable to harvest yeast from the bottom of the secondary fermenter at bottling time, or by top harvesting ale yeast as it is found in the foam during primary fermentation.

I recently reused yeast for the first time. I opted to harvest a pint of yeast/trub (placed in a sanitized jar) from the bottom of the primary after racking off the all-grain beer, and repitched about half of the yeast/trub a couple days later in a different style beer that called for that same variety of yeast.

The wort fermented practically over night (when I checked the gravity it had dropped to the desired level). Did I follow an acceptable practice, or am I likely to end up with off flavors in my second batch of beer off of the same yeast (consider that I used good sanitation)? I realize that autolysis could contribute to off flavors in the second batch if the yeast/trub was exposed to wort for too long a period.. I had fermented on the trub for eight days with the first batch, and plan on racking off the trub after five days in the second batch.

- Steve Smith

RESPONSE:

Steve, Yes, you did follow acceptable practice. Usually the shorter the time until you repitch the yeast the better. If your fermentation finished after one day that might indicate that you have over pitched a bit. 5-6 g of crop yeast slurry per liter of wort is a good pitching rate. Or since during fermentation yeast multiplies up to four, five times of the original amount you could use roughly a quarter of your crop yeast.

Acid washing the crop yeast makes sense if it is done properly; it will lower the risk of bacterial contamination. But you have to be careful with the temperature. Temperatures around 4 C guarantee higher viability than warmer temperatures above 10 C.

You can harvest the yeast when your main fermentation is finished and the yeast is settled. If your second fermentation is already finished after one day you can probably rack the beer off the yeast after 3 days. You are right that you can get off-flavors from autolysis if you leave the beer too long on yeast after the fermentation is finished.

Tobias & Forbes