Author Topic: How long can I let a yeast cake sit before reuse?  (Read 2608 times)

Offline majorvices

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Re: How long can I let a yeast cake sit before reuse?
« Reply #15 on: July 14, 2010, 07:03:45 AM »
professor and major, can you expand on what you do? when you go back and forth are you rinsing the yeast and then creating a new starter everytime? to me, it sounds like the OP was just going to toss a batch on top of an existing yeast cake, i'm assuming you guys aren't doing that.

I normally just reuse part of the slurry (I pour the slurry in a mason jar and refrigerate) - washing is a PITA and I never saw any real benefit from doing that (of course, I leave most trub and hop material in the kettle). If the slurry is over a couple weeks old I usually make a starter on my stir plate or with continuous o2.

As far as the acetobacter goes, its your call richardt - keeping it cold will help keep the slurry fresh. But if you are like me, if you have even the slightest doubt of its health and/or purity you will dump it. If you feel good about it - use it!
« Last Edit: July 14, 2010, 07:05:34 AM by majorvices »
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Offline richardt

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Re: How long can I let a yeast cake sit before reuse?
« Reply #16 on: July 14, 2010, 07:54:58 AM »
Thanks for the advice.  I do have a starter already on the stir plate as a back-up option.

Hypothetically, if an acetobacter infection takes hold in the yeast cake, would I be able to detect it by tasting a sample obtained aseptically? 
Or would I be unable to really tell due to the yeast bite?  I also assume it wouldn't look any different visually (i.e., it wouldn't look like a colony on a petri dish)?

Offline majorvices

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Re: How long can I let a yeast cake sit before reuse?
« Reply #17 on: July 14, 2010, 08:04:05 AM »
You will notice a net work of white webbing that starts to spread across the surface of the beer. It may smell slightly vinegary, but sometimes doesn;t seem to have any smell at all. The taste can be hard to pick up during the early stages of growth. The good thing about acetobacter is that it can not grow without the presence of o2, which is why I always limit the head space in my yeast slurry. It can't grow in Co2. The bad thing is that is seems to be very common. But, if you kept it cold you will most likely be alright. The reason I am so skittish about it is it is the infection I have been most commonly hit by. And like I said, I have seen it take hold in 48 hours on the surface of beer remaining on top of a slurry (after racking.) But that was also not refrigerated.
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Offline richardt

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Re: How long can I let a yeast cake sit before reuse?
« Reply #18 on: July 14, 2010, 10:15:03 AM »
Well, given that I just loosened/unsealed one side of the lid, but didn't remove it while transferring the beer to the keg hopefully means that there's still a CO2 blanket on top of the yeast cake (from the original headspace) even though some regular air entered the fermenter to equalize the pressure of the bucket during transfer.  I'll keep my fingers crossed and hope that I don't see any reticulated patterns in the cake this weekend.

Offline ndcube

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Re: How long can I let a yeast cake sit before reuse?
« Reply #19 on: July 14, 2010, 10:45:24 AM »
Well, given that I just loosened/unsealed one side of the lid, but didn't remove it while transferring the beer to the keg hopefully means that there's still a CO2 blanket on top of the yeast cake (from the original headspace) even though some regular air entered the fermenter to equalize the pressure of the bucket during transfer.  I'll keep my fingers crossed and hope that I don't see any reticulated patterns in the cake this weekend.

If your curious about CO2 just light a grill ligher and slowly move it into the bucket after you open it.  If it puffs out right away then there is good bit of CO2 in there.

Offline euge

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Re: How long can I let a yeast cake sit before reuse?
« Reply #20 on: July 14, 2010, 05:02:29 PM »
I had a rash of infections a couple of years ago. Acetobacter. Now I can pretty much spot it by the faintest whiff or taste and certainly by sight.  You'd be surprised how many expensive craft and European brews I've bought that were infected.

Now batches go into the kegs no longer than 10 days once FG is stable. If the brew tastes ok at that point the slurry is either used immediately or not at all. I avoid using yeast a third time.

And yes I like to keep dried yeast around since it is so handy, cheap and reliable.

I don't like reusing yeast which to do effectively and safely one needs a microscope and the right technique(s). Bacteria may be present in the first batch in minute amounts and not enough to affect the brew but in successive batches they will make themselves known. Not that it can't be done or tried but is definitely advanced homebrewing.   
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Offline ndcube

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Re: How long can I let a yeast cake sit before reuse?
« Reply #21 on: July 18, 2010, 04:39:39 AM »
I don't like reusing yeast which to do effectively and safely one needs a microscope and the right technique(s). Bacteria may be present in the first batch in minute amounts and not enough to affect the brew but in successive batches they will make themselves known. Not that it can't be done or tried but is definitely advanced homebrewing.   

It seems to me that the batches I make that use a saved yeast cake turn out better than the ones I make a starter for.  I don't think it's for only advanced homebrewers as long as you keep things clean and sanitized.

Offline majorvices

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Re: How long can I let a yeast cake sit before reuse?
« Reply #22 on: July 18, 2010, 06:10:08 AM »
+1 - I love reusing yeast and I often thing the second and third generation is far better. Also, if you have a lot of acetobacter infections I would recommend skipping the secondary and, if using buckets, making sure you get the beer out of the bucket and into the package as soon as possible once fermentation is over. Acetobacter can't grow under a co2 blanket. The only times I have ever seen acetobacter is in buckets or carboys where I let the airlock go dry.
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Offline babalu87

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Re: How long can I let a yeast cake sit before reuse?
« Reply #23 on: July 18, 2010, 02:53:35 PM »
+1 - I love reusing yeast and I often thing the second and third generation is far better.

+2

There are a few recipes of mine I wont brew unless the yeast has gone at least one fermentation prior.
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Offline euge

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Re: How long can I let a yeast cake sit before reuse?
« Reply #24 on: July 18, 2010, 03:55:57 PM »
I don't like reusing yeast which to do effectively and safely one needs a microscope and the right technique(s). Bacteria may be present in the first batch in minute amounts and not enough to affect the brew but in successive batches they will make themselves known. Not that it can't be done or tried but is definitely advanced homebrewing.   

It seems to me that the batches I make that use a saved yeast cake turn out better than the ones I make a starter for.  I don't think it's for only advanced homebrewers as long as you keep things clean and sanitized.

Oh no I never said not to do it! In fact my last batch was a fresh repitch. My theory as to why it's better is that there's alot more yeast and they are more active. Just be forewarned that infections can crop up this way no matter how sanitary one is. It would be wise to check yeast health and for bacteria and for that one should use a microscope.

That being said I'd be reluctant to use yeast from a high-gravity beer. They've been through the wringer at that point.
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Offline richardt

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Re: How long can I let a yeast cake sit before reuse?
« Reply #25 on: July 18, 2010, 06:29:39 PM »
Good advice all around guys.  I appreciate it.

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Re: How long can I let a yeast cake sit before reuse?
« Reply #26 on: July 18, 2010, 07:44:25 PM »
I've got a jar of Frankenyeast that I occasionally use and/or re-propagate that is maybe a decade old. Started out as something, Windsor or Nottingham maybe, dumped into a pint jar w/tin foil on top in the fridge. I use it occasionally in my 7% lawnmower by just dumping in the whole pint and then pouring another pint full after racking. If it has been awhile - a couple of months maybe - I start feeling sorry for them and will make a gallon starter out of some saved up and canned 3rd runnings just to give them a little treat. I have no idea how many generations have evolved or even what they have evolved into.
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Offline The Professor

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Re: How long can I let a yeast cake sit before reuse?
« Reply #27 on: July 19, 2010, 08:17:08 AM »
professor and major, can you expand on what you do? when you go back and forth are you rinsing the yeast and then creating a new starter everytime? to me, it sounds like the OP was just going to toss a batch on top of an existing yeast cake, i'm assuming you guys aren't doing that.

After primary fermentation, I save the yeast in a flask which is then simply covered with foil and stored in the back of my beer fridge.  I don't wash the yeast...I've tried it and it's a pain and makes no difference in the results, so I don't bother. 

When reusing yeast, the only time I do a starter is if the yeast has been in storage for more than 4 weeks.  Other than that, 1/3 to 1/2 of the stored slurry is all that's needed for the next batch. 
I totally agree with other observers that the flavor improves considerably after the yeast has gone through a few re-uses. 

My house yeast is like tubercle's "Frankenyeast"...I've kept it going for 20 years and counting and it's used for 90% of the brews I make.
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Offline hopaddicted

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Re: How long can I let a yeast cake sit before reuse?
« Reply #28 on: July 20, 2010, 06:41:14 AM »
This may seem like a stupid question, but it has been befuddling me since I've began reading about repitching yeast, how is repitching yeast and different than the yeast companies harvesting them?

I get that some of the yeast is going to be 'worn out', I understand there could be mutations (biggest difference, since scientific knowledge is a huge gap betweeen two processes) causing some variability, and the growth environments are different. Is the environment the key difference? Yeast harvesting I am assuming they are pump with oxygen throughout to keep them reproducing versus in a beer where we are trying to avoid adding additional oxygen. I could be way off base, far from my area of expertise.
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Offline majorvices

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Re: How long can I let a yeast cake sit before reuse?
« Reply #29 on: July 21, 2010, 05:25:37 AM »
I believe the difference is that the yeast are grown under aerobic conditions similar to when we use a stir plate or continuous O2. This gives them stronger cell walls and better sterol reserves. Regardless, as you alluded to, when WL or WY harvest their yeast they are at peak viability. When we harvest yeast from the bottom of a fermenter much of it is dead and the cells have depleted much of their sterol reserves.

As an aside I have been growing yeast under continuous aeration and collecting the slurry and it is pretty amazing how much healthier they seem. Fermentations start quicker and don't seem to take nearly as long as with slurry or 1st gen starters.
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