Why do you want to move it to a second fermenter?
Because my homebrew book says...
Secondary fermentation
Secondary or two-stage fermentation is all about conditioning your beer.
When you brewed at the beginner level, you put the fresh wort in the primary
fermenter, let the yeast do its thing, and then you bottled the beer. The beer
had about two weeks to condition in the bottle before you started sucking it
down. You did the right thing (within the limitations of your equipment and
expertise), but now you can do more.
At the beginner level, taking the freshly fermented beer out of the primary
fermenter was necessary not just because the initial fermentation was over,
but also because all those little yeasties, fresh from a gluttonous feast, were
about to start decomposing. Thats right, enzymes in the sugar-starved
yeast begin to break down the yeast cells. This horrific event is called yeast
autolysis. Autolysis can impart a sulfury, rubbery stench and flavor to your
beer. So leaving your fresh, young beer sitting on that bulging layer of
self-destructing yeast dregs is akin to allowing your child to wallow with
pigs in the mud and you dont want to smell either one of them when
theyre done. Racking your beer over to a secondary fermentation vessel
effectively leaves most of the sedimented yeast and other organic matter
behind.
So if bottling the beer after one week worked before, why cant it now? It still
can, but now that youre introducing more ingredients into the brewpot, the
added flavors and textures in your beer need more time to blend together. By
allowing the beer to undergo a secondary fermentation, you promote a mellowing
process that makes a noticeable improvement in your beer.
Considering the advantages of secondary fermentation
Allowing your beer to age in a secondary fermenter before you bottle it also
reduces yeast bite, the harsh flavor and mouthfeel associated with having
excessive yeast sediment in the bottle.
Because the yeast has eaten most of the consumable sugars in the wort
during primary fermentation, secondary fermentation yields very little yeast
activity and rarely produces a measurable amount of alcohol. This second
fermentation period is just an opportunity for all the beers ingredients
to acclimate to one another and establish a good, friendly (and tasty)
relationship.
The secondary fermenter represents a world of new possibilities for your
brew. You can add many different additives and flavorings to the secondary
fermenter that may have a huge effect on the finished beer. (See Chapters 8
and 9 for ideas on what to add at the secondary fermentation stage.)
The two-stage aspect of secondary fermentation also allows you to perform
some real beer-improving feats:
Dry hop: You can impart more hop aroma to your beer by simply adding
1⁄4 ounce to 2 ounces of hops (in pellet, plug, or whole leaf form) to the
secondary fermenter and then draining your beer over them. You can do
the same thing with spices, too. Chapter 5 has more information on this
process.
Make true Lagers: In order to make genuine Lager beers, you must age
the beer in the secondary fermenter for at least a few weeks at very cold
temperatures (32 to 40 degrees Fahrenheit) for proper flavor development.
Clarify your brew: You can add various clarifying agents to the
secondary fermenter to speed up the process of clarification. Typical
finings and clarifiers include isinglass, gelatin, Sparkalloid, and PVPP.
One final vote in support of secondary fermentation: By using this procedure,
you can not only quit worrying about unfinished primary fermentations
(and exploding bottles), but you can also actually cut the primary ferment
short by a day or two if that helps you rack the beer over to the secondary
fermenter at a more convenient time. This shortcut is possible only after the
peak fermentation activity subsides (usually by the fifth or sixth day of a
normal, healthy fermentation).