Author Topic: Timing question regarding secondary fermentation  (Read 1875 times)

Offline dunngood

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Re: Timing question regarding secondary fermentation
« Reply #30 on: October 25, 2016, 09:18:15 PM »
I was also referring to books by Greg Noonan when he states with a clean fermentation, it is usual for the beer to be held in the primary fermenter for two to three days after the kraeusen head has fallen. And the beer not be racked off its yeast sediment until diacetyl has been reabsorbed.
I get the idea that the primary yeast cake helps in some way with this process.

Offline brewinhard

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Re: Timing question regarding secondary fermentation
« Reply #31 on: October 25, 2016, 09:24:21 PM »

I get the idea that the primary yeast cake helps in some way with this process.

Yes, it simply allows more yeast in contact with the beer to allow for more fermentation byproducts to be absorbed, consumed, and transformed.

Offline Phil_M

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Re: Timing question regarding secondary fermentation
« Reply #32 on: October 25, 2016, 11:14:27 PM »
One of my biggest concerns about racking off the primary yeast cake to soon is the yeast has not cleaned up the off flavors yet.

Doesn't quite work like that....here's some info from John Palmer that will appear in an upcoming BYO article I'm writing....

Yeast have 3 phases in their life cycle: Adaptation, High Growth, and Stationary. (See Yeast by CW and Jamil) They do not have a maturation phase where they clean up byproducts. Adaptation phase is where they take in oxygen and build sterols and other lipids, assess the sugar composition and build enzymes, etc. Once those activities are done, they start the High Growth Phase, eating and reproducing. The number of cell divisions is limited by their lipid reserves they made during Adaptation. These reserves are shared with each daughter cell. When those lipid reserves are exhausted, the cell stops reproducing. In addition, when those reserves are exhausted, the cell is old and cannot eat or excrete waste efficiently across it’s cell membrane. A yeast cell typically can reproduce about 4 times during a typical fermentation, after that it is old and tired and tends to enter Stationary phase where it shuts down most of its metabolism and flocculates, waiting for the next batch of aerated wort. Stationary phase is essentially an inactivity phase, resting on the bottom.

Like I said, no conditioning phase as far as the yeast are concerned. Byproducts can be consumed at any point during the high growth phase, but they are a lower energy source than sugar, so guess what? Byproducts are not a biological priority. The brewer therefore needs to plan his pitching rate and fermentation conditions such that the yeast run out of fermentable wort sugar before their lipid reserves are exhausted and they go into stationary phase. Now you have a majority of vigorous yeast that have only undergone 2 reproductions (for example), the sugar is gone, and they are still hungry, so they turn to acetaldehyde and diacetyl as alternate energy sources and maturate the beer. You can help this by doing a diacetyl rest by raising the temperature a few degrees after the first half of fermentation, to keep the yeast active and eating. Where in the fermentation? after the first half, 2/3 to 3/4, when most of the attenuation has occured and raising the temperature is not going to cause rampant growth and the off-flavors associated with it.

Ok, this has me intrigued, and explains a good bit. With open fermentation with top droppings strains, some breweries skim the yeast off the top and keep re-oxygenating in order to try and keep the yeast in the growth phase.

It'd be interesting to try and see what sort of affect this has on home brewing...going to have to re-read the yeast book and try again...
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Offline JJeffers09

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Re: Timing question regarding secondary fermentation
« Reply #33 on: October 26, 2016, 02:13:33 AM »
Top cropping yeast isn't "re-oxygenating" the wort.  It is obtaining a fresh culture of yeast for the next batch man not oxygenation.  Yeast gets all of its O2 during the Lag phase not the growth phase.  Or at least that's not what most Ph.Ds say on the matter...

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Offline Saccharomyces

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Re: Timing question regarding secondary fermentation
« Reply #34 on: October 26, 2016, 04:21:24 PM »
The stage where the yeast cells are resting is known as "quiescence."  The stationary phase occurs when the yeast cells have reached maximum cell density or carbon has become limiting (sugar is carbon bound to water; hence, the term carbohydrate).  During the stationary phase, reproduction is for replacement only.

The risk of oxygenation is low until the yeast cells have been filtered from the beer.  Any yeast cells that are still in suspension during transfer will rapidly consume any O2 that is picked up.  The decision to rack should be made on what one wishes to accomplish.  When bottom cropping, the beer should be racked into a maturing vessel shortly after fermentation has subsided.  One does not want the yeast cells that are still in suspension to settle into the crop, as those cells usually have lost their ability to floc (aggregate), which is a common mutation. 

Separating the medium floculating cells from the early floculaters in the crop can be accomplished by swirling, allowing the heaviest fraction to settle, and cropping the topmost 250 to 350 milliliters of the liquid fraction.  Most of the cells in that part of the crop should be medium flocculaters that are still viable.


Offline ynotbrusum

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Re: Timing question regarding secondary fermentation
« Reply #35 on: October 26, 2016, 06:05:46 PM »
The stage where the yeast cells are resting is known as "quiescence."  The stationary phase occurs when the yeast cells have reached maximum cell density or carbon has become limiting (sugar is carbon bound to water; hence, the term carbohydrate).  During the stationary phase, reproduction is for replacement only.

The risk of oxygenation is low until the yeast cells have been filtered from the beer.  Any yeast cells that are still in suspension during transfer will rapidly consume any O2 that is picked up.  The decision to rack should be made on what one wishes to accomplish.  When bottom cropping, the beer should be racked into a maturing vessel shortly after fermentation has subsided.  One does not want the yeast cells that are still in suspension to settle into the crop, as those cells usually have lost their ability to floc (aggregate), which is a common mutation. 

Separating the medium floculating cells from the early floculaters in the crop can be accomplished by swirling, allowing the heaviest fraction to settle, and cropping the topmost 250 to 350 milliliters of the liquid fraction.  Most of the cells in that part of the crop should be medium flocculaters that are still viable.

Great info, as always, Mark.  You indicate that the yeast in suspension will consume the O2 from the racking process.  My concern is whether it is best to rack a point or two Plato above FG to ensure this O2 consumption or to attempt keg priming to assure that yeast scavenge the O2.  Thinking stability of the finished beer here...also whether to use an auto siphon or avoid it for oxidation concerns.
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Offline dilluh98

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Re: Timing question regarding secondary fermentation
« Reply #36 on: October 26, 2016, 09:03:19 PM »
Any yeast cells that are still in suspension during transfer will rapidly consume any O2 that is picked up.  The decision to rack should be made on what one wishes to accomplish. 

Mark, is aerobic oxidation of fuel necessary to scurb this oxygen? If not, what is the pathway for uptake of this oxygen ingress by the yeast?