Using yeast several times question

Hi everyone,
Is it possible for me to rack wort (that completed primary) to secondary fermenter and pour fresh cooled wort into the primary fermenter in order to use the yeast for the second time?

Thanks.

 

You can do it but it's not recommended. You'll be overpitching most likely, plus you'll be putting all of the trub, hop debris, dead yeast cells, etc. in your new batch.

It's better to rinse the yeast in sterile water before re-using. Check out the yeast washing illustrated sticky for directions on how to do this, and mrmalty.com for info on amounts of slurry to pitch.

 

if i do this, i try to reuse about a quarter of the cake

 

From this it is obvious that overpitching is inevitable however the trub, hop debris and the dead yeast cells will eventually settle to the bottom as they did in the first batch, am I right?

Another thing I wanted to ask was, can I use the rinsed yeast immediately after harvesting? Or should I store it for some time and pitch it?

 

This^^^^^^^.

If you're going to reuse it immediately, there's not really a need to rinse. Either leave 20-30% of the yeast cake for an ale (twice that for a lager) in the fermenter and pitch new wort atop that. Or you can harvest the same amount and pitch in a clean fermenter. You should adjust that up or down depending on the gravity of the new wort.

 

+2

You actually only need 1/10th of the yeast produced, but due to cell death from the alcohol 1/5th is a safe number. If you want lots of yeast character then I would do 1/10th of the cake.

If you're interested in the science behind how much of the cake to use check out my blog. (The blog is a little scattered, but my book is much better organized)

 

So the trub from the previous batch is not an issue? Do you have any recommendations on how to take three quarters of the yeast cake out of a carboy? Just pouring would not be good as I cant measure precisely how much of the yeast cake I am leaving behind?

 

i would tend to pour out my visual estimate of 3/4 of the cake. you could also pour it all out into something sanitized and scoop the slurry.

a loose fresh cake for me tends to be about 1.5 quarts, a quarter of which is about 1.5 cups. this becomes dependent on the composition of your trub though.

if you want precision, using some portion of the yeast cake is probably not for you

 

1ml of slurry is about billion cells. Honestly that is at least as close as a starter calculator will get you. There are just so many variables when propagating yeast.

If you really want to know, you'll need to do a cell count. Here is how:
http://woodlandbrew.blogspot.com/2012/11/amscope-binocular-compound-microscope.html

 

I've sanitized a plastic spoon and used that to scoop out the extra yeast cake. You can put that excess in a sanitized jar to rinse and store for later if you want.