Reusing Yeast with out washing... Pitching onto an active yeast cake... Pro's and Cons

A common practice in home brewing is washing yeast.   It is a fairly easy process, and I do it.  I especially do it with expensive or interesting yeasts that I want to preserve.  The process is detailed over and over again on the interwebs.  Don Osborn has a great video of how to do it on his YouTube channel.  If you haven't discovered "Don O" yet, you should.   He is a home brewer like us.  He has a lot of knowledge to share, but he's also still learning and perfecting his beers and his processes.  When he shoots his videos, he sometimes looks at the camera and gives himeself a note... like "remember extra cara 60 next time, the color is off".  It is a lot of fun.

The basic process of yeast washing is to pour your dregs into progressively smaller containers letting them settle each time, and leaving behind the trub, adding pre boiled and cooled water as needed. You are trying to get the milky active yeast that is just above the trub.  So you carefully pour off the low yeast wort, then you carefully pour the yeasty wort into a new container, then you let it settle (cold crashing can help) and you repeat till you have about a mason jar full of clean active yeast.   It will keep in your fridge for months.  There are adequate live active cells to ferment additional batches.


But there is another way.  An easier and maybe better way.  Just pour the new wort onto the old yeast.   It will take off like crazy.  No starter, No additional packages of yeast.

This video was shot just hours after a double brew day. These batches were pitched onto existing yeast cakes. Bonus footage of an APA that is clearing up nicely.  As you can see the fermentation is going strong.  It was so strong in fact that I had to add additional purified water to each of the fermentation locks. These were both medium gravity beers.   They finished primary in 96 hours at 64 F, falling from 1.048 and 1.062 to 1.01 and 1.013 respectively.

It is a great way to save money and pitch onto healthy yeast, but there are a few things to remember.  

• Always pitch onto a yeast that is appropriate for that style of beer. You don't want to try to create an Imperial American IPA on top of a Saison yeast.  You won't get the results you want.
• A simple strategy is to always pitch the same size batch.  Dont pitch a similar OG beer that is a smaller batch.  In other words dont pitch an 1.050 2.5 gallon batch onto a 1.050 5 gallon yeast cake.  That would be an over pitch.   You may pitch a huge beer onto a smaller batch.   In other words,  If you make a 1.040 pale ale 2.5 gallons and you are now making a 1.11 Barley Wine 5 gallons batch,  you will be fine.   
• Aerate -  There is no oxygen left in the yeast cake.   My strategy is to pour the wort onto the cake, and then pour back and forth between another fermenter a couple of times to get it aerated.  
• Always move from lower to higher OG beers.   There is risk of over pitch.  The compounds that yeast throw off early in fermentation are more complicated than just alcohol.  But you can mitigate this risk by moving up the OG chain.   
• My recent strategy
• Session IPA with new US05  1.042
• American Pale ale on the old US05  1.066
• White Stout (high og blonde ale) on the old US05  1.080
• Don't reuse yeast more than three or four times.
• Yeast (like all living organisms)  mutates over time.  These changes aren't noticeable in early generations, but may be very noticeable in later generations. 
• I know you've heard that you can use yeast over and over and over.  This is after all what commercial breweries do.  I will remind you that there are people with biology degrees working at commercial breweries, and they have expensive lab equipment to make sure everything is exactly how they want.  

It's an easy cost saving quality improving method you can follow.  Let me know what you think.