[MattyAHA]

I hear lots of people advocate to leaving beer in primary even after fg has been reached to clean up undesirable, and that makes sense to me, but what if your beer hits fg in only 4-5 days and tastes good, no weird flavors, should be fine to go ahead and keg right? If it tastes good i can't see why not, any reason to leave it longer?

[tommymorris]

I hear lots of people advocate to leaving beer in primary even after fg has been reached to clean up undesirable, and that makes sense to me, but what if your beer hits fg in only 4-5 days and tastes good, no weird flavors, should be fine to go ahead and keg right? If it tastes good i can't see why not, any reason to leave it longer?

To me there can still be diacetyl waiting on cold temperatures to emerge.  I always wait about a week. That doesn’t mean waiting is necessary. That’s just what I do.

[dmtaylor]

You can keg whenever you want.  Bottle bombs are the real problem.

[Bob357]

Once terminal gravity has been reached, the yeast is done cleaning up. If you're bottling, be sure the gravity is stable for 48 to 72hours.

[fredthecat]

Once terminal gravity has been reached, the yeast is done cleaning up. If you're bottling, be sure the gravity is stable for 48 to 72hours.

would love to hear more info about this suggestion. anyone? not stating it is true or false.

[Bob357]

 My copy is out on loan, so can't look it up and tell you the page number, but it comes from the yeast book by Jamil and Chris White.

[ynotbrusum]

And of course there is spunding....

[majorvices]

Once terminal gravity has been reached, the yeast is done cleaning up. If you're bottling, be sure the gravity is stable for 48 to 72hours.

would love to hear more info about this suggestion. anyone? not stating it is true or false.

There is nothing "magically" happening once the yeast is done fermenting the beer. If the beer is finished fermenting it is done. The only exception is for diacetyl and a quick forced diacetyl test is all you need. If you have a sous vide put a sample of your beer in a sealed jar and rest it at 140-160 for 40 minutes, cool, then smell and tste. If you don't smell or taste diacetyl you won't have any issues with diacetyl reforming in your packaged beer.

You can also do the same test in a microwave, heat to 140-160 and rest (wrap it in towels, put in cooler or place in oven preheated to 170. Wait at least 10 minutes, 40 for best results.)

One big benefit of waiting to package your beer, however, is leaving behind hops and yeast sediment. I usually hold the beer for at least 3-4 days at cold temps after fermentation. But if you want to let the sediment drop out in the kegs that's up to you.

[tommymorris]

One thing I will add is after getting a Tilt my definition of when fermentation is complete has changed. I ferment in a clear plastic carboy. I used to wait until the yeast had noticeably flocculated and the krausen was gone. Then I would wait a few more days (but often longer for my own convenience). Then I would take one SG reading and not worry about 3 days of stable measurements.

Now I have a Tilt. If I follow the rule that fermentation is complete when the gravity is stable for three days, and never look at the beer, I end up waiting about the same amount of time as above.

My point is some of my answers about waiting a few more days are relative to how I define completed fermentation. In both cases above I would be comfortable packaging the beer.  I usually don’t because my schedule allows more time, but I have packaged beers that quickly without any issues.

Now, if someone says do a fast fermentation test to predict FG and then package immediately when the beer reaches the predicted FG, that would make me nervous.

[denny]

Once terminal gravity has been reached, the yeast is done cleaning up. If you're bottling, be sure the gravity is stable for 48 to 72hours.

THIS^^^^  I asked John Palmer about this and this was his answer, too.

[denny]

Once terminal gravity has been reached, the yeast is done cleaning up. If you're bottling, be sure the gravity is stable for 48 to 72hours.

would love to hear more info about this suggestion. anyone? not stating it is true or false.

This was Palmer' s response to my question....

100-150 years ago, fermentation was open, followed by maturation in a wooden cask. The beer
was prone to contamination. This could be mitigated by heavy hopping and long warm
maturation to wait for the bitterness to die down, or by long cold maturation (lagering) to use
temperature to keep the contamination down.
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.
Today, we have closed stainless steel tanks which allow us to prevent oxidation, pull the yeast,
and control the temperature. This plus our understanding of the yeast cycle above changes the
way we ferment lagers, so now lager beer fermentation is started cooler to control yeast growth
and allowed or controlled to rise during fermentation to the diacetyl rest, such that ALL of the
fermentation and maturation is complete before the beer is cooled to lagering temperature. The
effect of temperature at this stage is strictly physical, increasing the strength of hydrogen bonds
to coagulate beer haze and help it settle out. The yeast are still susceptible to temperature shock
and lipid excretion, so the cooling to lager temperature 35-38F still has to be slow, i.e. 5F per
day.
Please note that this behavior and fermentation technique is applicable to ALL beers, not just
lager beer.

[MattyAHA]

Excellent! thank you Denny for that

[fredthecat]

Once terminal gravity has been reached, the yeast is done cleaning up. If you're bottling, be sure the gravity is stable for 48 to 72hours.

would love to hear more info about this suggestion. anyone? not stating it is true or false.

This was Palmer' s response to my question....

100-150 years ago, fermentation was open, followed by maturation in a wooden cask. The beer
was prone to contamination. This could be mitigated by heavy hopping and long warm
maturation to wait for the bitterness to die down, or by long cold maturation (lagering) to use
temperature to keep the contamination down.
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.
Today, we have closed stainless steel tanks which allow us to prevent oxidation, pull the yeast,
and control the temperature. This plus our understanding of the yeast cycle above changes the
way we ferment lagers, so now lager beer fermentation is started cooler to control yeast growth
and allowed or controlled to rise during fermentation to the diacetyl rest, such that ALL of the
fermentation and maturation is complete before the beer is cooled to lagering temperature. The
effect of temperature at this stage is strictly physical, increasing the strength of hydrogen bonds
to coagulate beer haze and help it settle out. The yeast are still susceptible to temperature shock
and lipid excretion, so the cooling to lager temperature 35-38F still has to be slow, i.e. 5F per
day.
Please note that this behavior and fermentation technique is applicable to ALL beers, not just
lager beer.

awesome. thanks. this is something people new to brewing in 2020 and beyond should read before their first batch.

im very tempted to do a well nutritioned, appropriate starter size batch and go for brew to bottling in a week. (assuming FG is reached)