Monday, April 18, 2011

Washing Yeast

I keep things pretty simple when in comes to using yeast, pitch a large, healthy amount. I feel confident in the beer quality if I can get a quick and vigorous ferment to occur within twelve hours. If I'm using the dry packets like Safale, which are inexpensive enough to be generous, I pitch three packets directly into ten gallons of aerated wort. I don't bother re-hydrating the yeast. If  I use Whitelabs liquid yeast I step the colony up a couple of times to about 200 billion cells for ten gallons.

I have a plan in mind for subsequent beers to ferment that will get racked directly onto the yeast cake of the previous beer. Generally, I rack to the yeast cake two or three times. Subsequent batches ferment out withing three to four days because of the size and health of the yeast cake in the fermentor.

If I decide to salvage the yeast after fermentation, I will use a sanitized utensil (Pyrex measuring cup) to scoop the yeast from the bottom of the fermenter into a sanitized jar for storage. Or, as seen here in a previous post, I will pull out a liner bag and drain they into a sanitized container. Keep in mind that I ferment in open fermentors and that accessing the yeast is very easy. I'm comfortable storing the yeast in the fridge this way for as long as six weeks. Then, when ready to re-use, I take the yeast out at the beginning of the next brew session to acclimate to the warmer temperatures. After the new batch of wort is chilled and aerated, I will simply pitch the entire content of the jar into the wort. I don't concern myself with the hop debris, protein coagulates and general sludge that is mixed in with the yeast, and I will repeat these steps in salvaging and re-using yeast as often as is convenient.

Having said all that, there is a way of cleaning up the yeast or washing/rinsing out the spurge material. It is a series of steps that involve diluting the yeast sludge with sterile water and pouring off the foreign debris that rises to the top and that settles to the bottom of the mixture. The middle area contains the healthy, viable yeast cells.

Normally when I save yeast it looks
 like this (unwashed), and I would
typically just pitch it as is

Pouring off the liquid
that is at the top of a
container of salvaged yeast


Agitate and watch as it starts to seperate

Adding sterile water to the
salvaged yeast slurry

In any case, here are the steps to washing your yeast:
Pour off the excess liquid from the top of the container of salvaged yeast
Fill the container with sterile water (in my case I boil and cooled filtered water)
Agitate the jar until completely mixed, don't leave any lumps intact.
Let mixture rest until there is a clear separation of the three layers (you should be able to see a lighter layer in the middle that is formed by healthy yeast.

Once the separation is clear (20 to 30 minutes) gently pour off (discard) the top layer, then pour the middle layer (yeast) into another sanitized container and discard the bottom layer

A clear seperation of the three areas, the
light middle area is the healthy yeast and you
 can see it congregating at the bottom (light area)

Again, pouring off the excess liquid

This is a look after a second seperation is complete

With the yeast now in a new container repeat the process to clean even further.
Repeat as many times as you wish but keep in mind that the probability of introducing contaminates like bacteria and wild yeast will increase with each step.

This is the final results.
Pretty clear liquid covering
a healthy yeast cake

After a third repeat filling with
sterile water and agitating

I hope this was helpful and although I don't personally use this technique I can see the value in it. You could probably store the yeast longer under these conditions and it would be easy to step up a culture from washed yeast to create a very large and healthy colony. Any feed back on this subject is definitely welcome. Cheers!

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