Why to yeast stop when they do?

[pcrawford]

Why to yeast stop when they do?

I had a beer that went from 1.048 to 1.012 and tasted a bit sweet. I wanted to get it down lower and be nice and dry. I used the Belgium yeast and it sat in the secondary for 3+ weeks. This baby did not want to ferment anymore and the Belgium yeast was done at 1.012. So I kegged it up and dumped in a packet of dry yeast I had in the fridge. I’ll let this sit in the basement for a week before I cool it down and drink it. I’m hoping the yeast I added will help being the gravity down a few more points and dry this beer out a bit.

So this brings me to a question. Why did the Belgium yeast stop? Is it a certain ratio of alcohol to sugar and then they are like, no we are done? Why when I add a new yeast will they kick up again and eat more sugar?

1. Will they eat some more sugar? I doubt the dry yeast will attenuate 70% of the sugar left, but why?
2. If I added a nice new fresh batch of Belgium yeast will they attenuate more? I bet they won’t but don’t know why. They will be like, my buddies stopped at 1.012 and I should also. But why?
3. How much of the remaining sugars will the dry yeast eat up? When will they stop?


Also let’s pretend I aerated appropriately and pitched the correct amount of yeast. I’m not all that interested in that. But rather under idea yeast conditions why did all the above happen?

Give me some good biology here with some nerd terms.

Thanks!

 

[VTBrewer]

You got 75% attenuation, and the amount of cells you had left in there couldn't metabolize any more sugar. 75% is very good for most yeasts, you'd have to look up what the attenuation for your particular belgain strain is.

I'm not sure what repitching after a healthy and complete fermentation would do, nor would I try it.

 

[Suthrncomfrt1884]

read this... It will give you a basic knowledge of what you're asking.

How to Brew - By John Palmer - Nutrients

 

[david_42]

The unfermented sugars are too complex (aka large) to pass through the yeast cell's walls and/or the yeast cannot break the chains down into smaller sugars. Only simpler sugars, like sucrose, fructose, maltose, etc. will ferment.

 

[pcrawford]

I guess another way to think about my question is why do some yeast strains have better attenuation then others? How can some eat 80% of the sugar and others only 75%? Does it depend on the size of the yeast and what they can fit through their cell wall?

 

[Kaiser]

You should be able to find the answer here: Understanding Attenuation - German Brewing Techniques

Let me know if it didn't help. The intention of that article was to answer exactly your question.

Kai