Fresh Wort To Trub

[kevnlis]

I have a simple question, yet the answer is not so easy to find. If you reuse a trub and put a fresh wort over it, does that mean the yeast is now in a new generation? Say for instance you pitch a generation zero liquid yeast (it now becomes generation one), then you rack the beer off the trub and put a fresh wort onto that yeast, it is now generation two?

I am going to reuse the trub I currently have going for my next brew tomorrow, I am not sure if I should harvest, wash, take my cultures and then pitch a new starter, or to just use the trub as it is. Obviously I want to avoid another generation before I harvest.

 

[Fents]

Cant answer your question, to technical for me.

but i did make a brew last week and for the first time decided to pitch straight onto a yeast cake. emptied fermenter leaving trub, cleaned krausen marks off with cloth and tipped it in. It's a US05. Talk about take off. Going in 20 mins, massive krausen on day 2 and still a pretty big one.

 

[Stuster]

Yep, that's right, kevnlis. Each batch you use the yeast for is another generation. I'd say get the beer off the yeast, save some yeast (jars are an easy way to do this), then you can clean the fermenter, new wort in, pitch in some yeast. You don't need all the yeast slurry, something like 250ml of thickish slurry should be enough for a standard strength beer. You can also save some of the yeast in the fridge (sealed container, minimal headspace) and use that for another batch.

I'm not quite sure what you want to know about the generations. It's still going to be a second generation yeast if you take it, wash it and make a starter you know. :unsure:

 

[kevnlis]

With my cultures I consider the first use to be first gen. So the smack pack or pitchable vial is generation zero.

 

[Stuster]

Obviously I want to avoid another generation before I harvest.

I agree, I call the first time I use a liquid yeast it's the 1st generation, it was just this sentence I didn't really follow.

 

[MHB]

I would think you would have to call it a new generation every time the yeast goes back into the reproductive part of its life cycle.

Admittedly the amount of yeast that you are effectively pitching when you drop a fresh wort onto a yeast cake is going to be very high. The reproductive phase will be commensurately short (that is until all the dissolved oxygen in the wort is taken up by the yeast and it changes back to anaerobic fermentation).
So the chance that mutated cells will reproduce sufficiently to dramatically change character you expect from that type of yeast is reduced.

Like everything in brewing there are pros and cons:-

Too little yeast and you get a sluggish ferment, some metabolic side-issues produced by the yeast and an increased possibility of other micro flora taking hold.

Too much yeast isnt all good either, as the yeast reproduces it removes some undesirable components from the wort, (like lipids) these are important for the health of the yeast and we want them out of the brew (lipids are head negative and reduce the long-term stability of the beer).

A yeast cake also contains all the dead cells and other detritus that make up the trub, not all of these should be put back into a fresh wort, as they will eventually decompose and taint the beer.

I suppose what I am trying to say is that there is a right amount of yeast.
This is what Stuster is getting with his method, what he has suggested would work well.

There are other possibilities, when I have wanted a lot of fresh yeast I have added 5 Litres of highly aerated wort to the yeast cake, allowed it to start to ferment (goes off like a rocket) after about 6-12 hours, rack into 750 mL bottles with airlocks in them (leaving all the trub that stays on the bottom of the fermenter - on the bottom of the fermenter).

When the ferment is finished just cap the bottles and store in a fridge - you get a 10 or so huge pitches, without all the dead stuff.

The key thing is to not keep making new generations; every generation up's the odds of getting a bad brew.
Try to get as many brews as you can out of the first generation.

MHB

 

[kevnlis]

But the fresh wort will not be aerated? There will be no oxygen to cause the yeast to go back into the adaptation phase, they will just continue as per normal, except the wort will be fresh and not fermented.

This is the process I was going to use, I should have been more clear from the start.

Mash - Boil - Chill boil stockpot in ice bath - Rack to trub trying not to aerate

I know the yeast will be a new generation every time it sees oxygen and reproduces, but will it still be a new generation in this scenario?

 

[Muggus]

In the past I often used alot of the left over 'trub yeast' to brew my new beers.

From what i've experienced it seemed to work alright for reasonably neutral yeasts like British and American ale yeasts, though doesn't seem to attentuate as well or ferment out as fast. As for Hefeweizen and Belgian yeasts, it seems to not only work less effectively, but changes the yeast flavour quite a bit, more often than not for the worst, especially when you're after those kind of flavours. And as for lager yeasts...well lets not go there.

Most of the 'harvested' yeast came from brews using White Labs yeasts...had to make the most of them because of their price!
Interesting enough experiment though, handy to have some extra yeast for brews too.