Author Topic: Harvesting some yeast  (Read 1938 times)

S. cerevisiae

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Re: Harvesting some yeast
« Reply #15 on: July 02, 2015, 05:31:31 PM »
Wow. That's quite an explanation. I had to read it twice just to make sure I got it all. Isn't it almost impossible to create a 100% sterile environment as a homebrewer? I clean and use Starsan like a lot of people on here do to create a sterile environment. If this isn't the best of most effective way shed some light!!

You are not creating a sterile environment by sanitizing. You are creating a sanitary environment.  Sanitary means that most of the vegetative cells have been killed.  Boiling kills all vegetative cells, but it does not kill spores.  Autoclaving (pressure cooking at 121C/250F under 15 pounds per square above normal atmospheric pressure) kills everything.  White Labs does not boil their propagation media.  They autoclave it.  I autoclave my slants, plates, and first-level 40ml starters, and use aseptic transfer technique while working with this media to maintain a sterile environment.

By the way, Star San is a bactericide, not a full-spectrum microbiocide. Star San belongs to a class of sanitizing agents that are known as acid-anionic sanitizers.  Acid-anionic sanitizers have limited ability to kill yeast and mold.  I learned that lesson the hard way. 

Offline reverseapachemaster

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Re: Harvesting some yeast
« Reply #16 on: July 02, 2015, 05:33:06 PM »
This is what I do pretty much every batch. It's the healthiest yeast in my brewing process and if spare yeast is going to end up in a mason jar anyway it might as well get there without going through the beer and all the other opportunities to pick up uninvited guests.

I see home brewers make this incorrect assumption all of the time. However, nothing could be further from the truth.  Unless one is performing aseptic transfers into wort that was autoclaved in the vessel in which the yeast is propagated and stored, pitching a starter from a starter provides little to no advantage from a contamination point of view over serial repitching from normal gravity (sub-6% ABV) batches.  Boiled starter wort is not sterile, and neither is a sanitized or boiled starter vessel.

If the processes compared are:

1. Make a starter, unload the starter liquid with some of the yeast into a sanitized mason jar; or

2. Make a starter, unload the starter into a sanitized fermentor, use sanitized bottling equipment to remove the beer, then unload some of the trub into a sanitized mason jar;

Then I hardly see how the first is a less effective method of yeast recovery if only because less sanitized, but not sterilized, equipment is coming in contact with the beer.

I'll agree with you that if the comparison is either of the above processes versus pitching new wort directly onto some or all of the trub from a prior batch then certainly that direct pitch is a superior process. However, when I brew I am almost never brewing another batch immediately after the next and often not brewing sequentially with the same yeast. So either way that yeast is going in a mason jar. I also have to store fermentors in an area where there is a lot of dust that finds its way to the exterior of the fermentors. These are screw top one gallon jugs for the most part. It's difficult to get them effectively clean to pour out the yeast without picking up an infection. I've tried with a near 100% success rate of picking up a very aggressive infection. Going directly from starter to mason jar has solved that problem. That's why I qualified my answer that this is the best option for my brewing process rather than insist it is best for all.
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S. cerevisiae

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Re: Harvesting some yeast
« Reply #17 on: July 02, 2015, 06:07:39 PM »
If you are serially repitching, do some of the cells from the original generation stick around for subsequent fermentations?  At what point do the cells from the original generation die off to be replaced completely by newer cells?

Yes, a percentage of old cells are cropped with the new cells.  The larger the difference between the inoculation rate and maximum cell density, the higher the ratio of new to old cells.    However, there is a tradeoff in that we want to ensure that the pitched culture is large enough to rapidly "own" the culture.  The number one limiting factor in bottom-cropped yeast is contaminant load.  There is an opportunity for whatever intruders have made their way into a culture to multiply each time it is cropped and repitched.  That's why proper handling of initial pitches is critical.  For the most part, the cleaner the initial pitch, the longer a bottom-cropped culture can be repitched.  Top-cropped cultures are an entirely different animal.  They rely on the dynamic that wild yeast and bacteria generally do not crop to the top (i.e., if one captures a culture in the wild that top crops, one has more than likely captured a domesticated yeast strain), which why top-cropped yeast can be used almost indefinitely if handled correctly.

We have all been told to crop from the middle of the cone. The reason behind this recommendation is three-fold.  The first reason is obvious in that the bottom of the cone contains most of the break.  The second reason is also somewhat obvious in that we do not want to crop cells that exhibit early flocculation because that practice can result in a culture becoming progressively more flocculent.  However, another reason for not cropping from the bottom of the cone is that it contains dead and older less viable cells that we do not want to pitch into our next batch.

A scar is left on the surface of the cell wall every time a yeast cell buds.  As yeast cells take in nutrition and expel waste products through their cell walls, bud scars affect a yeast health.

Budding yeast and bud scars

« Last Edit: July 02, 2015, 10:28:13 PM by S. cerevisiae »

Offline coolman26

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Re: Harvesting some yeast
« Reply #18 on: July 03, 2015, 03:10:49 AM »
Is there a better sanitizer than StarSan?  I wonder how I've not had more infections with my plastic fermenters.
Jeff B