yeast lifespan, when to harvest when keg fermenting?

[odie]

I often ferment in the serving keg so my question is when would be the better time to harvest? On the first pour of the last?

If I'm using a standard dip tube, the yeast is collected on the first couple pints. So probably withing a month of fermentation ending.

If I'm using a floating dip tube, the yeast must stay in the bottom of the keg until the last pint is served. So might be 6-12 months until the yeast cake is harvested (I do have as many as 10 taps going so some kegs might last a long time).

Once the yeast is finished and dormant, I assume it's pretty much decaying at a normal rate, whether in the bottom of the keg or in a pint jar.

I guess my question is would yeast harvested from the bottom of the keg after the last pint, say 6 months, be considered the same viability as yeast harvested on the first pint at 1 month and stored in the fridge 5 months? Or would the yeast left in the keg be considered "fresher". Assuming both kegs were done at the same time, so both yeasts were originally pitch at the same time. One stays dormant in the keg, the other is transferred to a mason jar and put in the fridge.

If I was planning to do another beer quickly, obviously harvest up front and keep that yeast going. But if it was going to be 6 months...does it make any difference if the yeast is harvested and saved early or just leave it in the keg until it's time?

 

[Somesaymybeerisdrinkable]

Sounds like you have an excuse to get some lab equipment so you can count yeast cells from different harvest.

Since you would need to make a starter either way for six months old yeast I'm not if any difference would matter.

 

[odie]

trying to have less equipment. I got way too much brew stuff as it is.

 

[Bassman2003]

I am learning yeast storage and use practices all of the time. It is tricky but is becoming more clear and simple as well. Basically, you do not want to store yeast with any oxygen involved. Oxygen is their fuel and if you keep them in an environment where they can get oxygen they will be active. When they are active the use up resources just like we do. If there are no new resources for them to eat (long term storage) they deplete their own resources and wither away.

So, in homebrew scenarios, keeping yeast in a keg (CO2 environment) is way better than in a mason jar (O2 environment). Breweries use "brinks" which are purged kegs to store harvested yeast on a CO2 environment. Homebrewers can do this too with soda bottles and Kegland Tees.

For your scenario, keeping the yeast in the keg is the best approach (one and six months time frames). If you do take it out on the first pour, then either use it in 1-2 weeks or transfer it to a soda bottle brink for storage. As far as will it last six months, you just have to try and see how they do.