Question about harvesting yeast

I have a question or two about harvesting spent yeast that I want to run by all you knowledgeable folks.

It seems I have set up a cycle of sorts with my brewing. I brew every other or every third week. This means that the batch I am brewing and the batch I am kegging are very close in time (I have not secondaried any of my beers yet, I usually just let them "finish" in the keg). I usually rack the finished batch on a friday and brew on a saturday. I would like to try reusing my yeast. I know that I could just put the new batch on top of the old yeast cake and may try this with my current setup as I am going from a light cream ale to a little fuller APA. My question come as follows:

1. how "old" of a yeast cake can I just add onto? My 2 week old cream ale cake I would think would be okay, but what about 3 or 4 week old cakes?

2. If I rack off the cake on a friday and capture the yeast with sterile water, how long can I wait to use it before making a starter? If I use it on saturday? Sunday? I would think that if I waited till the next weekend, then I would need to rejuvinate it with a starter? Do I need to make a starter with a yeast cake no matter what?

As your questions suggest, there are a number of ways that you could go about this. I suggest that you stick to a more proper pitching rate instead of dumping on the whole cake. I've done it and wasn't too awful happy with the results. If you rack on friday and brew on saturday, use Mr. Malty to figure out how much slurry you need to pitch to the next batch. I wouldn't worry with a starter at this point since you have plenty of yeast, but if you want to re-energize them then make a small starter right after you collect the yeast and pitch the whole thing on saturday. If you rack and save the yeast in sterile water for a period of time, then definitely make a starter.

Just followed your link. You appear to be the yeast guru! Thanks for the info.

jamorgan3777 said:

Just followed your link. You appear to be the yeast guru! Thanks for the info.

Click to expand...

Thanks, but, I'm definitely no guru

You will definitely want to look into yeast rinsing (or washing). This is a fairly simple process if you can work in sanitary conditions.

Here is a good PDF of the process by Bill Nevits. If you look on page 3, the picture of Step 5, you will see the layers of what is in the bottom of your fermentor once you get everything resuspended and settling out in a tall narrow jar. You want to siphon off the top layer and discard, this is proteins and other junk. The middle layer is the good yeast, save this. Discard the bottom layer of hop particles and break material.

I let the good layer settle out in smaller jars, then use Mr. Malty and the actual yeast slurry volume and date harvested to figure out my pitch rate. There are a lot of ways to reuse yeast, but this way will get you a consistent result and result in more consistent beers.

Thanks for the additional references. I cant wait to give this a try.