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I'm about 6 batches into my AG brewing and my fridge is slowly getting filled with jars of yeast I've been harvesting, each labelled so I can tell which batch they came from.

So far I've been harvesting yeast only from the primary fermenter but I'm thinking about harvesting from secondary too because, at the moment, I don't want to force natural selection on my yeast population, but this will increase my yeast volume even more.

In theory all of the yeast I've collected is of the same strain barring a few inevitable genetic mutations, so my question is this...

Am I wise to keep all my yeast harvests separate, should I mix my primary and secondary harvests from the same batch, or can I mix all of my harvests together into one big, amorphous, yeasty jar?

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You might consider just upping the size of your yeast starter and harvesting from that. – Scott Jan 23 '14 at 15:25
As Scott suggests, harvesting from your starter will give you the best chance of keeping the strain more like the original, but in the end, after a few generations, you will have a distinct "house strain". – Wyrmwood Jan 23 '14 at 23:25

I assume they're all different re-pitches of the same original strain? Certainly you would want to keep different strains apart so you can pitch based on their desired properties.

But even still, I would keep the harvested yeast separate, if only so you can use them in a FIFO order of collection.

The method you're using the harvest yeast has a reliable shelf life of approximately 2 weeks, and a maximum shelf life of 6 months, according to Zainasheff and White in Yeast. As such, I would endeavour to use the harvested yeast ASAP.

I would only suggest harvesting from the primary fermenter, and employ the "yeast rinsing" technique to separate the yeast from the other trub. Yeast harvested from secondary are going to be composed exclusively of "late flocculators" that will skew your yeast population.

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Yes, all harvests of the same type of yeast. My thinking is if I mix all harvests together I will end up with a combination of old and young yeasts in the same population, older ones providing nutrients for the viable, younger yeast. If I harvest the primary fermenter only won't I generate a population of early flocculaters, if so is that a bad thing? – Doug Jan 23 '14 at 16:03
If you harvest from primary, you'll get early-, normal- and some late-flocculators, unless you're harvesting before primary fermentation is finished. I wouldn't worry about trying to provide "old" cells as nutrient for "new" cells, but I also don't think mixing the harvests would be a horrible idea. – jsled Jan 24 '14 at 13:45

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