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Old 10-20-2007, 05:56 PM   #1
oooFishy
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Default Final Gravity!!!!!

Yesterday I checked up on two of my beers, one being a heffeweizen and the other a big IPA. Both are for-sure done fermenting.

To my surprise the Heff's F.G. was higher than expected- 1.021- although, it tasted like a finished beer and not sweet at all. It's O.G. was 1.050, so strangely it ended up being only 4%abv! according to my hydrometer. It was a PM and I used the Heffeweizen IV yeast (either Wyeast or White Labs). My IPA on the other hand was at 1.010, from a 1.071 O.G. (8%abv) and was slightly sweet like I wanted it. I used California Ale yeast for that one. Both yeasts have the same attenuation and similar optimum fermenting temperatures. What do you guys think caused the discrepancy in their final gravities?

I thought that higher F.G.'s were caused primarily by unfermentable sugars. If this is the case then why is my IPA sweet and my Heff dry?

Gravity has me very confused. Alcohol is less dense than water, right?, so couldn't a beer with a high alcohol content potentially mask its denser properties like sugar? This may be the case with the IPA.

But then why is the Heff which doesn't seems to have any lingering sugar have a high F.G.? Do other things in beer contribute to gravity readings?



I hope someone feels up to tackling these questions. I'm a little hungover, so that explains the less than eloquent outline of my situation.

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Old 10-20-2007, 07:11 PM   #2
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Are you correcting your hydrometer readings for temperature, both the OG and the FG?
Your hefe seems to have a high FG vs. my experience - could me you mashed at high-ish temp and got more unfermentables out of it, or you had a wheat extract that had a higher proportion of unfermentables...

The IPA is sweet -- what were your calculated IBUs? Could it be insufficient hops giving the sweet taste?

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Old 10-20-2007, 07:20 PM   #3
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1. Yes I corrected for everything
2. The Hefe was done at 149F- my effeciency sucked so it was basically a PM
3. The IPA is fine. Over 100 IBUs and not overly bitter at all. Good subtle sweetness- mashed it at 155


These really aren't the variables I suspect contributed to the weirdness

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Old 10-20-2007, 07:23 PM   #4
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149F? You should've got a really thin beer there. Carful you don't have bottle bombs. Are you positive it was done fermenting? DId you try swirling it?

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Old 10-20-2007, 08:30 PM   #5
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The Heff is being cold conditioned in a keg. If it wasn't done fermenting yet for some reason, is there any way to get it going again? I can't imagine why it stopped fermenting at 1.020. It was in the 2ndary for a month within its ideal temp range after a seemingly good week in the primary. Now its off the yeast cake in a keg. The beer tastes OK except for being waaaay too bitter. I never knew 20 IBU's could be so intense. Heff yeast and hops really aren't friends I guess. Gotta learn some way. California yeast and hops and best buds tho .

On another note- can anyone comment on the relationship between gravity-sugar-alcohol-and other stuff in beer like protein. It seems to me like gravity (density) isn't just a direct measure of sugar dissolved in wort/beer. I am really interested to hear what people have to say on this.

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Old 10-20-2007, 10:42 PM   #6
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Hefe's like WARM conditioning, not cold. Take it out of the fridge, rouse the yeast off the bottom and let it sit at room temp a bit longer.

In general, most yeasts attenuate at 75%. This means your FG should be about 25% of your OG. Example, OG: 1.048. Divide by 4 = 12. Your FG should be 1.012 or somewhere in that neighborhood.

If it's a higher FG it'll be sweeter and lower in alcohol %, a lower FG will be drier and higher alcohol %.

Another factor is the IBUs of the hops. If your brew is sweet then you underhopped.

Since your brew stopped fermenting at 20 then it either pooped out or got stuck. Rousing it and raising the temp usually gets it kick started again.

I don't know your recipe so I can't comment on it. My HW recipe is so simple. I do 1.5 gal boils with 1 lb of DME and only 3%AA (no way near your 20) for 45 mins and remove the pot from the flame. I add the remaining malts and let them steep for 15 mins. Done. I top off to 5.25 gals. I prefer my HWs on the sweet side like many German Weizens.

You could make a sweet batch and mix them to balance both. I always recommend blending 2 bad (opposite) brews to create one good one. Unless it's infected/medicinal, there are ways to cover up many brewing "mistakes".

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Old 10-20-2007, 10:54 PM   #7
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As you say, gravity isn't just a measure of sugar dissolved an a liquid, it is the density of that liquid compared to that of pure water at a given temperature.
Before you start fermenting, , your wort is made up primarily of water, sugars, and other stuff. You can ignore anything that isn't dissolved (trub), as this doesn't affect the gravity. You can also ignore just about everything else dissolved in the wort as it either makes such a small difference to the gravity that the typical hydrometer isn't accurate enough to measure it (especially if your eyesight is like mine) or it is going to remain in the finished beer.
As the wort ferments, the yeasts convert the sugars (heavier than water) into alcohol (lighter than water) and carbon dioxide causing the gravity to drop. (The weight of the beer will be reduced by the weight of the carbon dioxide released. The volume will also probably change slightly.) The yeast also metabolizes other compounds in the wort, but again, the gravity changes caused by this are insignificant.
When fermentation is finished, the change in gravity can give a fairly accurate estimation of the amount of alcohol produced..

Hope this answers your question.

-a.

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Old 10-21-2007, 05:25 AM   #8
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I guess I'm gonna try and get the gravity down a little more before giving up. With 73-80% attenuation, worst case scenario the F.G. should be 1.013. I've wrapped a sleeping bag around the keg to get the temps into the high 60's lo 70's. The optimal fermenting temp is 66-70, but it was closer to 66 during my long 2ndary ferm during which the fermentation got stuck, so I'm gonna try a little higher this time. Any other tricks to get the floating yeast started again. It's a low flocculating strain, so this gives me hope there's still enough friends floating around in there.

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