Basic Priming / Secondary Fermentation Question

[milestron]

Hey all just got a question which is almost too embarrasing to ask but I figure if I can get my head around everything then surely that is the key to making better beer. I've just purchased another fermenter to act as a secondary and have a beer racked into it at the moment. It was in primary about 3 weeks and now secondary about the same and is completely fermented, ready to bottle, sitting at room temperature maybe 16 to 18 degrees.

What I'm trying to understand is what's the deal with the dead vs alive yeast? I get that the yeast cake which formed in the primary is pretty well spent ie dead, having used up all the available sugars, so where does the yeast required for priming come from? Is it just that there will always be some residual living yeast haningaround, staying dormant until it gets something else to eat? Will it eventually die if it's left in secondary too long without any fresh sugars? I suppose that all the living yeast cells are in liquid form and just transfer across with the beer and that all the old yeast stays in the primary to get chucked?

Cheers first up for any replies, all the biology I know is from Attenborough docos. I've read a few articles on priming but they are mostly about the 'how' and not the 'why' if you get what i mean

 

[pk.sax]

Take a small sample of the beer In a bottle/flask or whatever and drop some dissolved glucose (dextrose) or even simple sugar into it. Clingwrap the mouth of it and put a rubberband over it. If your yeast is alive and kicking, you're gonna see it take that sugar up. Problem solved.

 

[Wolfy]

Actually the vast majority of yeast that you (most likely) discarded from your primary was most likely very healthy and viable (many people harvest, 'wash' and reuse that yeast, many breweries have done the same for 100's of years).

When yeast has finished fermenting it starts to flocculate and go dormant, with no new nutrients it will slowly starve and die, but once it's in a state of 'hibernation' under the right conditions it can live for extended periods of time (months or years).

By transferring to secondary, you are removing the beer from the trub, which includes a large portion of yeast, however there are still millions (maybe even billions) of viable yeast cells left suspended in your beer, these are responsible for conditioning and improving your beer as it ages in the secondary (many people do not actually us a secondary, since they feel that the larger mass of yeast allows for better conditioning).
During the secondary, condition or lager processes, more of the yeast will settle out, especially if you let it sit for some time, refrigerate and/use fininings in an effort to produce bright (clear) beer.
But even after all that there is usually still enough alive viable yeast to bottle condition your beer - once you add a dose of sugars and they wake up again.

If you were to filter your beer, or leave it in secondary or to lager for extended periods (months) much of the yeast will have settled out or died, and you may need to add new yeast when you prime, but in most normal circumstances (bottling within 4-8 weeks) there is still (usually) enough yeast alive in suspension (even if you probably can't see it) to bottle condition and prime your beer.

 

[kocken42]

Hey milestron,

Your question is definitely not a stupid one, nor should you feel embaressed to ask.

The trub at the bottom of primary consists of malt sediments, dead yeast cells, very much alive yeast cells, water sediments and a heap of other things which settle out of solution. There is always HEAPS (millions of millions) of yeast cells floating around in the beer, it's just they are so small (individually) you can't see them with the naked eye. The only way to get rid of all of them completely is with a sterile filter.

The cell count will eventually start to deteriorate as they consume food, alcohol increases, oxygen decreases etc...but yeast are amazing creatures and kinda like the Jurassic Park line "Life always finds a way". When you go to bottle, you are giving the remaining yeast some oxygen and some food, and they will keep plugging away, it just may take longer to carbonate as they increase cell numbers again if you have a seriously low yeast count. Considering that your beer has stayed at 18 ish degrees, there will still be plenty of yeast floating around...once you bottle it will again begin to settle to the bottom.

It's funny because we just consider yeast as that grainy, smelly stuff that comes out of the packet but its been manufactured that way to be dried stored etc. Wild yeast occurs on grapevines naturally, and therefore you can ferment wine without adding a cultured yeast! unfortunately, wild yeasts can only ferment to about 6% until that alcohol level deteriorates them, so after that point a cultured yeast takes over...which is generally ALL AROUND a winery or brewery...it will be on walls, buckets, spoons, floors, all equipment...sneaky buggers.

 

[milestron]

aahh i get it - probably those little yeasties are alot tougher then what i was giving them credit for

cheers guys thanks for your time

 

[Wolfy]

aahh i get it - probably those little yeasties are alot tougher then what i was giving them credit for

In general, much tougher, but mostly when you are talking billions of cells, there is a fair chance that at least some will survive most 'abuse'
But they still survive best when we treat them right.