Feeding yeast and alcohol

HomeBrewTalk.com - Beer, Wine, Mead, & Cider Brewing Discussion Community.

Help Support Homebrew Talk:

Brewno

Well-Known Member
Joined
May 1, 2006
Messages
365
Reaction score
2
Location
PA
I have one of those dumb questions.
This is purely a "for my own knowledge" question. You know one of those "I wonder what would happen if..."
Sometimes asking these simple questions helps me to learn the science behind something. Not only why something happens but also why it would not.
I think I may learn why it would not with this question so here goes.

Now, the yeast feeding on starches/sugars creates alcohol and carbonation right?
When the yeast settled and churning has stopped I would imagine that feeding has slowed to a minimum. I'm sure there is still activity going on but most of the "food" has already been consumed and some of those hungry little yeasties have lost interest and went to relax at the bottom. Now you take your hydrometer reading and get your FG and approx. alcohol %.

Here's the question: If you were to shake up the batch and get some of those fat lazy yeasts back up and swimming about, would they begin feeding on the remainder of the sugars thus raising the alcohol percentage? Or is there so little left that the difference would be minimal? Or does it just not work that way?
I'm also considering that you add priming sugar later and that would have an effect also but that doesn't change your FG which in essense is your alc content.

Sorry, I just like information like this.

Tommy
 

cweston

Well-Known Member
Joined
Feb 2, 2006
Messages
2,014
Reaction score
23
Location
Manhattan, KS
Adding priming sugar *does* increase your alcohol content a small amount. I believe the formulas that homebrewers use--like (OG - FG) * .129 is the one I'm familiar with--take that into consideration.

It's possible sometimes to gently rouse overly flocculant yeast back into suspension and get it to ferment a bit more. Generally, you don't want to shake up and oxidize your beer, nor do you want to shake the trub that's settled out back into suspension.
 
OP
B

Brewno

Well-Known Member
Joined
May 1, 2006
Messages
365
Reaction score
2
Location
PA
cweston said:
Adding priming sugar *does* increase your alcohol content a small amount. I believe the formulas that homebrewers use--like (OG - FG) * .129 is the one I'm familiar with--take that into consideration.

It's possible sometimes to gently rouse overly flocculant yeast back into suspension and get it to ferment a bit more. Generally, you don't want to shake up and oxidize your beer, nor do you want to shake the trub that's settled out back into suspension.

Ahh yes, the little details that escape the beginner. Sloshing or poring too vigorously would add too much oxygen. The inductions come back to me now:eek:

Transfer your beer gently...no splashing.
And the sediment that forms on the bottom of the fermenter is called "trub" I guess?

Thanks

Tommy
 

david_42

Well-Known Member
Joined
Oct 8, 2005
Messages
25,582
Reaction score
182
Location
Oak Grove
Some sugars are not fermentable by yeasts (but are by gut bacteria), also there are proteins that add body, mouthfeel and flavor in the final product.

Yep, trub is the sludge.
 

Latest posts

Top