Fermentation question

[2ducks]

So,I started home brewing with wine, got a few batches in the works that need some aging and decided to brew some beer while I'm waiting. I picked up a Bavarian Hefeweizen extract kit that's it the fermenter doing well for the past couple days. OG 1.049, down to 1.020 today. The kit says final gravity should be 1.010.
I know with wine making the yeast will continue to ferment until they either run out of sugars (SG<1.000) or until the alcohol content is higher than he yeast can tolerate and they die off.
I guess my question is why would this not be the case in beer? Obviously the yeast aren't dead if they start to ferment again when priming sugar is added. Are some of the sugars in beer just not fermentable?
I like to understand the science behind what is going on and would eventually like to get in to all grain brewing.

 

[AkTom]

Here's a noobie answer. There are fermentable and unfermentable sugars. The yeast eat what they can. They wait patiently for the priming solution. Also typically wine yeast can tolerate much higher alcohol levels.
It sounded better in my head.

 

[2ducks]

Your theory sounds the same as mine and makes sense, just wondering if there's more to it.

 

[AkTom]

I'm sure there is.

 

[CA_Mouse]

Extract tends to have more unfermentable sugars than all grain does. You can try raising the temperature of your fermenter, that will encourage the yeast to eat a bit more of the remaining sugar. Rarely have I gotten an extract beer below 1.016-1.018.

 

[PADave]

Yep, you got the infamous extract 1.020 FG. Do a search, not uncommon.

 

[eadavis80]

A lot of people complain about the "1.020 curse" but I've never had that problem. In fact, I think the highest FG I've had in over 50 extract batches was 1.016. But, back to the OP, yeah - there are some sugars that are unfermentable so the yeast will just eat what they can. Plus, as was stated, wine yeast is generally much more alcohol-tolerant than beer yeasts. Never bottle beer before FG is stable - meaning your gravity readings are identical over a 3-day window. If you bottle prematurely, you can end up with bottle bombs - no good.

 

[beergolf]

It sounds like it has only been a few days. How long has it been fermenting? Give it some more time. Check again at about 2 weeks and I would guess that your gravity will have dropped.

Wort does have some unfermentable sugars so depending on the recipe, the yeast will eat what it can and stop when the fermentable sugars are all consumed. So that explains different FG numbers for different recipes.

The FG number is just an estimate, so you may miss by a few points, but that is OK as long as it is stable, before you bottle.

A lot of people mention the extract 1.020 curse, but back when I was doing extract I never had any problem getting my beers to attenuate. I even had extract saisons get down to 1.004. A good proper sized, healthy yeast pitch and you should have no issues reaching the FG. What yeast are you using and what temp are you fermenting at?

Just step back for a little while and let the yeast do it's job.

 

[boydster]

So,I started home brewing with wine, got a few batches in the works that need some aging and decided to brew some beer while I'm waiting. I picked up a Bavarian Hefeweizen extract kit that's it the fermenter doing well for the past couple days. OG 1.049, down to 1.020 today. The kit says final gravity should be 1.010.
I know with wine making the yeast will continue to ferment until they either run out of sugars (SG<1.000) or until the alcohol content is higher than he yeast can tolerate and they die off.
I guess my question is why would this not be the case in beer? Obviously the yeast aren't dead if they start to ferment again when priming sugar is added. Are some of the sugars in beer just not fermentable?
I like to understand the science behind what is going on and would eventually like to get in to all grain brewing.

You are just a couple days into fermentation, so it makes sense that it would be at 1.020-ish at this point. Give it time, it'll keep working down to whatever final gravity it lands on.

As for why the yeast doesn't get the beer down below 1.000, it's because there are some sugars in wort that the yeast can't ferment. Even if you pitched wine yeast instead of beer yeast, the beer would still finish higher than 1.000. It has to do with how long of a chain the sugar molecule is - the shorter, simpler sugars are fermented while the longer chain sugars are not. The must you use for making wine doesn't have those more complex sugars in it.

 

[2ducks]

Thanks guys, sorry I should have been more specific. I'm not worried about the current 1.020, only on 3rd day. Activity has slowed but still going on. I'll watch it for a few more days and maybe give it a stir later if it doesn't continue to drop.
Mostly I was just wondering about why wines always finish at 1.000 or less unless there was a problem or just too much sugar, where beer wouldn't necessarily do that.
It makes sense that wines are almost entirely simple sugars either from fruit or table sugar where a wort may have more complex sugars

 

[seabrew8]

It sounded better in my head.

That was funny dude.

 

[AkTom]

That was funny dude.

Thanks. I'm here for you.