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Old 07-25-2011, 05:10 PM   #1
Skipper74
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Apr 2011
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This weekend, I brewed a repeat batch of the same beer that I bottled earlier in the day, so I just dumped the new wort on the old yeast cake (Safale 05). The airlock on the new beer began showing activity within hours and fermentation was rolling along within 12 hours.

This was the first time I re-used a yeast cake and I was impressed with the time it saved me. (I didn't even have to wash the fermenter from the first batch. For my next batch, I will be brewing a darker, stronger beer, so I believe that I can again re-use the yeast cake. Since it will now be two generations in, however, I am wondering if I should scoop out some of the trub/yeast from the bottom before adding the new wort (using a sanitized measuring cup). Has anyone ever done this?

 
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Old 07-25-2011, 05:14 PM   #2
Kahler
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Personally, i would wash the yeast. Essentially, you could move you beer to the bottling bucket, wash the yeast, and by the time you bottle the first batch and brew the new one, you could have "clean" yeast to pitch. This way you are using just the healthy yeast cells.
And when i wash, i end up with enough yeast to pitch into three more batches...and if you use a starter you can stretch it even further.

 
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Old 07-25-2011, 05:49 PM   #3
nefarious_1_
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I would also wash the yeast, then make a starter. This ensures you're not overpitching (which you are when pitching directly onto a yeast cake, unless the next batch is significantly larger than the previous ie. several times larger) and using only healthy yeast cells without any trub/undesireables.

It's pretty easy to wash yeast and make a starter, so I say why not? Your beer will benefit.

 
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Old 07-25-2011, 07:31 PM   #4
Skipper74
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If I wash the yeast can I pitch it without using a starter? I have never used a starter before when pitching dry yeast into the cooled wort and always had great fermentations. Having to make a starter to reuse washed yeast just seems like an additional step I'd like to avoid if possible.

 
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Old 07-25-2011, 07:50 PM   #5
nefarious_1_
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Yes, you can pitch the washed yeast without making a starter.

Mr. Malty has a calculator for figuring that out. Use the "yeast slurry" function.

Also, from Mr. Malty regarding repitching yeast:

Quote:
There are about 4.5 billion yeast cells in 1 milliliter of yeast solids (solids with no excess liquid). According to Fix, in a slurry, only about 25% of the mass is yeast solids. Of course, if there is a lot of trub in there, you have an even lower percentage of yeast solids. The bad thing is that you can't tell how viable that yeast is, unless you have the equipment to properly test and count it. So this is where it gets a little bit like black magic. There are a number of factors that affect the viability of a given pitch of yeast. How old is the yeast? How stressful was their last fermentation? Have they had the proper environment and nutrients for successful reproduction or are they too scarred and tired to go on?

When the yeast is fresh and healthy off an previous batch, viability is maybe around 90%+. It goes down from there fairly quickly without proper storage and it also really depends on the strain of yeast. Unless you're going to get into testing viability, you're going to need to make some educated guesses and keep good notes on the results. This is where being a yeast psychic really helps. Start in a range of 80 to 90% viability and you probably won't be too far off. Use the Pitching Rate CalculatorTM to help figure out how much of that yeast you need. If your yeast viability is much lower than 90%, you should probably toss the yeast. If you really want to use it, you might consider pitching it in some starter wort to get the still viable cells active. When they're in solution, decant that active part of the starter into another vessel, hopefully leaving the dead cells behind.
Making a starter with the washed yeast, IMO, is the best assurance of yeast health and a good start.

 
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Old 07-25-2011, 07:55 PM   #6
david_42
 
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I don't wash yeast, but I do limit the amount of slurry to a quart or so. At 25% cells, that's over a trillion.
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Old 07-25-2011, 09:34 PM   #7
RavenChief
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Quote:
Originally Posted by david_42 View Post
I don't wash yeast, but I do limit the amount of slurry to a quart or so. At 25% cells, that's over a trillion.
I also never wash yeast. I know that many brewers swear by it but I never have seen a good reason to do it. I just save about 8 oz of good trub yeast from the bottom of my primary in a "clean jar". I usually use it within a few weeks so I know it's still alive. Anyway I have reused the same yeast over 20 times and still it works like a champ.

 
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Old 07-25-2011, 09:49 PM   #8
sonvolt
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I've done it! I have simply pitched atop a yeast cake for a third fermentation. I didn't "wash" the yeast or anything.

It was awesome!

 
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Old 07-25-2011, 10:56 PM   #9
greatschmaltez
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I'm pretty sure this is a micro evolution problem I did in biology. By washing and using a starter, you always ensure, at least the best homebrewers can, that you are getting the best yeast cells (survival of the fittest, or in this case decanting off the fittest). Therefore you get the best fermentation. Some yeasts that are more forgiving to less than optimal fermentation conditions will result in having an expected result from just pitching on the yeast cake over and over again. But I'd guess (since I've never done this) that a less forgiving yeast like 3068 would end up giving an unsatisfactory result if you just repitched on the same yeast cake over and over.

Starter is so key in taking beer to the next level, aside from maybe temperature control. And it's so easy, I'd recommend doing one. We go through a lot of trouble on brew day and bottle day, an extra 30 minutes for a starter to ensure good fermentation just makes sense.

Anyways, just my 2 cents.

 
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Old 07-26-2011, 12:48 AM   #10
Skipper74
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I apologize if this is a stupid question (and maybe it shows that I do't really understand the process of making a starter), but if I am going to reduce down my yeast/trub cake to a 1 liter (or thereabouts) slurry anyway, instead of making a starter to ensure enough healthy yeast cells, couldn't I just dump 2 liters of slurry (presumably doubling the number of cells that were in 1 liter)?

Thanks for humoring my curiousity.

 
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