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Reusing Yeast from a completed batch

jopakent

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I emptied my carboys the other day, leaving a half inch or so of liquid on top of the yeast, and then put them both back in the fridge.

I was told that the yeast sitting there is very viable and ready to gobble some sugar and that all I need to do is put some properly oxygenated wort into it and agitate a bit to get things roiling.

I’m thinking this sounds pretty good, but I’ve got no clue on how to determine if there is enough viable yeast there or not. The two carboys were the fermentation vessels for a 10 gallon batch that I just decanted into aging kegs, so my thinking is that in the fermentation process (about 14 days) my initial pitch should have been well fed and grown some, so if it was enough for 10 gallons before fermentation, it should be more than enough after fermentation…  Is this a correct assumption?

I’m planning to brew on Saturday and I’m thinking of getting a yeast starter going today just to be sure I have enough.

I guess there are really two questions here. One, is there enough yeast in the carboys, and Two, is there a downside (besides $$) to pitching too much yeast?

TIA,
JPK
 
i haven't gotten in to doing this myself (i'm comparing yeast by splitting batches almost every brew), but can share the tidbits i remember reading:

optimally you're going to move from a lighter, lower gravity brew to a darker, higher gravity batch.  hopefully the OG of your previous batch wasn't much above 1.065.

you don't want to pitch the entire slurry... i remember 1/2-2/3 of it being thrown out there.

i have asked around a bit and haven't heard any specific downsides to overpitching, although avoiding doing so is obviously best practice.
 
I save yeast from one brew to go into others all the time.  I typically get around 5-6 generations before tossing it and starting over.

I do rinse the yeast using canned water (water which has been sterilized in canning jars using a pressure canner).  My process is like this:

Once the carboy is empty, I put the airlock back on it.  When I am ready to recover the yeast, I open a quart jar of the canned water and pour it into the carboy.

I will shake the carboy with the airlock on for about 3 to 5 minutes to break up all the trub and yeast and then allow it to sit for 20 to 30 minutes.  At this point the trub has mostly settled out and what is in suspension is light trub, hops and yeast.  I pour out a quart back into the sterilized quart jar and recap it.  I mark it and put it into my refrigerator for a couple of days.

If the yeast is pretty clean (off-white, no obvious trub) and there is little trub on the bottom of the jar, I will decant much of the weak beer on top and use it for the next batch.

If the yeast is pretty clean but there is a good amount of trub, I will pour off the weak beer, open another jar of water and pour about half the water into the jar with the yeast in it.  I shake and repeat the settling before pouring the water and yeast in suspension back into the water jar which is half full.  When that settles, I usually end up with about 40 to 50 ml of pretty clean yeast.

If the yeast is dirty (lots of trub still in the yeast, brown yeast), I will rinse it again as I described above and repeat that process until the yeast is white to off-white and looks pretty clean.  Generally, I will end up with 20 to 30 ml of yeast if I need to do repeated rinsing.

On brew day, I figure out how much yeast I will need, figuring that each ml of yeast will contain about 5 to 6 million cells.  I do discount that amount if the yeast does look like it has some trub in it.  To give a reference, a White Labs vial contains about a billion cells and when fully settled on the bottom of the tube is approximately 18 ml.

Once I know how much to pitch, I take my hydrometer sample and throw that into the jar with the decanted yeast.  Shake it up well and add a proportional amount equal to the number of ml of yeast I target. 

Over pitching:  I have done it a couple of times.  My experience is that a gross over pitch will result in lesser yeast character in the beer.  This is OK for some beers, but definitely bod for any beers for which the yeast character is a integral part of the style.
 
I've written several articles on this.  I've put fresh wort onto a yeast cake from a previous batch, however, I only do this when I'm making a big beer (1.090+).

I harvest yeast all the time.  There is a thread here that I started on yeast harvesting.

Here is that thread. 

http://www.beersmith.com/forum/index.php/topic,10396.msg43386.html#msg43386

You can also check out my blog below for the tutorial and other information on harvesting yeast, whether from a recently made beer or from your local (wild) environment.  There is an article about harvesting yeast from my Russian Sage bush in my back yard.
 
I guess I'm just lazy! I reuse yeast most of the time, but I don't "Wash" or build Starters and I let BeerSmith tell me how much slurry to use. It was only a pain once to set up! Now if I stay within reasonable parameters, I probably over pitch, which is far better than under pitching!! Here's how I do it:

I used the Mrmalty calculator with assumptions that were pretty much at the high end of my brews. They were, OG = 1.080, batch volume = 11 gallons, Slurry thickness was maximum at 4.5 billion cells/ml, and slurry was worst case 25% non yeast. I also assumed it would be stored for 4 weeks between use giving only 50% viable cells/ml.  Almost all of my brews fall well within these parameters which ensure I am over pitching but not extremely so.

From Mrmalty the, the 11 gallon batch of 1.080 beer required 600 billion cells. So, it says I need 334 ml of month old slurry. Since I'm lazy, I convert back to US units and rounding just very slightly, 334ml = 11oz. Using the 600 billion cells/11 oz indicates that my typical slurry has 55 billion cells per ounce.

I now create an Ingredient entry for "Blah blah blah yest slurry". The key item is that 1 pk = 55 billion cells. That pk is really one ounce of slurry. I do this out of convenience for each yeast strain I use by simply coping then pasting the strain. Edit the title to indicate a slurry. Change the cell count to 55 billion cells/pk.

When I build a new recipe, I select the yeast as the "slurry" we created. When I'm satisfied with the recipe, I open the "Starter" tab.  I look down to the  "Recommended Starter If using Liquid Yeast" section at the bottom and look at the "Yeast Packs To Use If No Starter". That is the number of 1 oz packs of slurry needed. I go back to the "Design" tab and edit the number of packs. So for my typical 11 gallon batch of 1.050 beer, I need 8 packs or ounces of slurry! Very easy once the above is entered.

To get started I make my typical batch using the indicated number of DRY yeast packs, hydrated before pitching. When I'm close to racking, I wash and sanitize at least two 1 pint wide mouth mason jars and lids. The lids have been punched in the center with a 1/2" punch and fitted with a 3/8" grommet to allow me to use a typical air lock. After I rack the beer off the yeast cake, I use a sanitized stainless steel ladle to fill the at least two of the jars. I put on the lids, put on an air lock, (I use cheap Vodka in the air lock"), and pop them into a little 2,2 cubic foot dorm style fridge I keep just to store my dry yeast inventory, the vacuum packed leaf hops I'm working with,(another story), and my jars of slurry.  Basically, I get two jars of slurry per brew. Each 16 oz jar is twice the 8 oz typically needed.

In practice, I only pitch 1 whole jar of slurry per future batch. I get two future batches per harvest. I only re-pitch 5 generations of slurry but since I get two jars per batch that's 10 batches of 11 gallons before I start over. The economy is great! My first batch needs two or 3 pks of dry yeast at $4.00 a pack is worst case  $12.00 per 11 batches of 11 gallons each. That's about $1.10 for yeast per 11 gallon batch or $0.10 per gallon. For me, Since I brew more session type beers so I only need 2 pks to start. You do the math.

By buying in bulk and re-pitching yeast, we are drinking our homebrew for about $0.15 a bottle!  ;D

Pat

 
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