Harvesting Yeast From a Corny Keg?

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Sep 24, 2020
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I was just about to harvest yeast from some bottles of commercial beer and I had a thought. Could you reuse the yeast at the bottom of a keg as soon as you drink the keg empty? Would the CO2 kill the yeast or are there any other pitfalls to this idea? I figured, maybe you could just pour it into a sanitized jar or cultivate it with a yeast starter. Has anyone tried this? Any experience? Any thoughts?
I mean, if you can harvest it from carbonated commercial beer bottles, you ought to be able to harvest it from a carbonated corny keg. Right?
Step up a couple times from a small starter, like with a yeast in a bottle, and it's most likely fine. Might be issues if pitched directly. Most of the cells - the late floccers - are probably immature and not as efficient at fermentation. A few growth cycles (step up starters) is going to help them mature and produce a better age structure in the yeast population
There will be very little yeast to zero harvest if you are fermenting and kegging "normally" since you would have cold crashed and racked from fermenter into the keg. Plus the dip tube is continuously purging any remaining yeast as you drink it.

Now if you are using floating dip tubes...

You can fermenting in the corny keg and just serve out of that same keg. When the keg goes empty a lot of trub and yeast will be ejected in mass. When that starts you can simply collect the last pour of the keg into a mason jar and let the yeast/trub settle out and reuse that.

Or you can just let the keg blow completely and there will still be enough yeast at the bottom to just dump fresh wort on top and call it good.
I once recovered yeast from a keg that had just kicked. It was a WY -PC strain that I really wanted to keep on hand, but I forgot to save it when kegging.

Even after cold crashing at 30F and gelatin fining in the conical, and then lagering for a month in the keg at 36F, and then serving for another month or so at 36F, it was fine.

I built it up in four stages to get to the 4 liter starter I needed for the next batch. Go for it!
Back in the home brewing dark ages of the 1940’s - 1970’s, one of the ways home brewers would acquire yeasts was from kegs. A lot of brewers had different procedures for packaging kegs than their canning or bottling lines that would make yeasts available mostly at the end of the keg. A lot of the canning and bottling lines were heavily filtered or Pasteurized, not always so with kegs. Some were even krausened in the kegs. Kegs were also advertised as being fresher, the brewers best work.

So, if you were able to get a keg that hasn’t been filtered, and had your timing right, you certainly could harvest some yeast. If you could estimate when the keg was about depleted, you could agitate or swirl the keg a bit to put any residual yeast into suspension, then pour off the final beer into a sanitized Snapple bottle or Mason jar for harvesting.

The only issue might be if the brewer was using some different strain for packaging. I suspect to simplify things most brewers would just use their house strains, so you would likely be good to go.

The same procedure would apply to a commercial or Corny keg.
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