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Old 07-09-2010, 05:16 AM   #1
Superhappyfuntime
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Default Questions about S.G. and why

Hey guys,

So working on my first kit, I started a Munich Dark Ale from Brew House with Wyeast 2206, no starter (just read about it last night). Surprisingly, a day and a half later, the krausen started forming. It's only a ball the size of two fists right now, but I trust it will grow.

My question is, this kit is 1.055 as per the website, but I only added 5L instead of 8L of water as per the LHBS to 'thicken' it up a bit for taste etc.

I took an SG today and it showed 1.042-4. I am confused. If I added LESS water, doesn't that mean the SG should be significantly higher? As the beer ferments, won't this drop the gravity even lower, meaning less alcohol? I adjusted for the temp measured at and I did pitch at 68 instead of the lower temp it asked for, but I didn't think that would make a difference.

Can anyone shed some light on this for me? Thanks in advance!

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Old 07-09-2010, 05:26 AM   #2
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Originally Posted by Superhappyfuntime View Post
Hey guys,

So working on my first kit, I started a Munich Dark Ale from Brew House with Wyeast 2206, no starter (just read about it last night). Surprisingly, a day and a half later, the krausen started forming. It's only a ball the size of two fists right now, but I trust it will grow.

My question is, this kit is 1.055 as per the website, but I only added 5L instead of 8L of water as per the LHBS to 'thicken' it up a bit for taste etc.

I took an SG today and it showed 1.042-4. I am confused. If I added LESS water, doesn't that mean the SG should be significantly higher? As the beer ferments, won't this drop the gravity even lower, meaning less alcohol? I adjusted for the temp measured at and I did pitch at 68 instead of the lower temp it asked for, but I didn't think that would make a difference.

Can anyone shed some light on this for me? Thanks in advance!
it has fermented some already thus dropping the gravity
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Old 07-09-2010, 05:30 AM   #3
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as the yeast eat the sugars in your beer they produce alcohol which will make your SG reading go down. to figure out how much alcohol is in your beer you need to know what the SG was BEFORE you added the yeast. this will tell you how much potential alcohol you have. then take another reading after fermentation is completely done. the difference between the two readings is the actual amount of alcohol in your beer.

the reason your SG reading was lower than you expected was because fermentation is already under way and the yeast have eaten some of the sugar and produced alcohol which lowered the SG reading.

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Old 07-09-2010, 05:39 AM   #4
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Thanks for the quick response guys! Unfortunately, I broke my Hydrometer during the mixing process, so I couldn't take it. So I guess I will have to accept I won't know the alcohol limit on this batch.

The yeast getting started point I guess was pretty common sense for me to know :P

So then, my question is this. When a mfr. says o.g. of 1.055, are we as brewers to assume the target potency of the beer based is that number, right (7.1%)? 1.055 on my hydrometer says 7.1% potential alcohol, so.... does that mean that when my fermentation is complete I SHOULD expect a proper F.G. of 1.005-1.010 to reach that 7.1%, if I have done everything correctly? (1.055-1.005 gr. = 7.1 pot (roughly))?

Is this how you would do the calcs, or am I off in space somewhere? :P

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Old 07-09-2010, 06:16 AM   #5
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Where did the hydrometer break? IN the beer????

There are 'technical' calculations based on yeast's efficiency (ability to eat up all the sugars it needs to, and convert to alcohol) (some are designed to leave some residual sweetness, others very dry; as well as temperature factors etc. But not many BEERS finish at "1.000"

A mfr. will say OG of whatever, because that's what it 'should' come out as. Some guys don't even bother checking OG or FG, they just make beer. Personally, I don't recommend that unless you've been doing it awhile and know when it is done fermenting enough to bottle!

Your FG, again, is dependent on 'when the yeast craps out' / what its alcohol tolerance is. BASICALLY, look at your staring gravity / potential for finishing all the way and subtract your final gravity / potential for finishing all the way. ie: if you have OG of "7%" and FG of "2%", you should kinda get a 5% beer.

Make sense?
And of course, hydrometers are calibrated to a certain temperature which 'should' be taken into account. Or just roll with it and use rough numbers.

Good luck.

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Old 07-09-2010, 06:22 AM   #6
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You need BeerSmith to calculate all of this for you - Try this in the meantime: http://beercalculus.hopville.com/ - I dont take SG readings anymore and more or less rely on data from that site and experience to tell me around what my SG is. Punch in your numbers on there and you can get a good idea of what you are looking at with your beer. If you really need to nerd it up and get exact, you need beersmith and be anal with your hydrometer.

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Old 07-09-2010, 03:11 PM   #7
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If the OG is 1.055 at 8L, then your OG was 1.088 at 5L.
Target OG * Target Volume = Current OG * Current Volume

Since its an extract kit its OK to miss the reading cuz it'll be what it was supposed to be. That's only OG though. Your FG will vary depending on aeration, yeast type, yeast viability, pitching rate, etc. so its generally good to check that. Plus it assures you fermentation is complete.

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Old 07-09-2010, 03:38 PM   #8
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S.G. - F.G. x 131 = ABV

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