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Old 03-07-2013, 05:24 PM   #1
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Default Hydrometer question

I've seen a few threads asking for help on a brew and the reply is, take a reading we can tell a lot from your hydrometer reading.

So as a noob what all can you tell from a reading? I get the SG and the TG for ABV and the fact you can tell whether your fermentation is done, anything else.

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Old 03-07-2013, 05:29 PM   #2
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TG? maybe FG? usually we talk in terms of Original Gravity (OG) and final gravity (FG), sometimes just gravity, etc.

Anyhow, yes what you've listed are the main things. But since people often post "my airlock isn't bubbling, is it fermenting?" or something similar, having the OG and current gravity is very useful. If the OG is 1.040 and now it is 1.035 and a week has passed, there is a problme, but if it is 1.010, then nope that is normal.

The point of the gravity reading is you can't tell if fermentation has completed without it. I have a nutbrown that I added honey to (1 of the 5 gallons) and until I take a rading I won't be sure it has completed. I keep seeing signs that there is still fermentation.

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Old 03-07-2013, 05:44 PM   #3
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The First gravity reading, (OG) before fermentation tells you how much sugar is dissolved in the wort. A higher OG means you have more sugar to ferment and potentially this means a higher potential level of alcohol.

The final gravity reading (FG) is the one you use to tell you how much of the sugar remains in the liquid.
So the difference between OG and FG tells you how much alcohol is in the beer (approximately).

Now, it is possible to get 6% ABV a few different ways. You could have a beer with a really high OG and a relatively high FG. This means your beer will still have 6% alcohol but will taste sweeter because some of the sugar didn't ferment out.

Or you could have a medium OG and ferment to a really low FG and still get 6% but with a noticeably less sweet (dry) beer.

How much of the sugar ferments depends on the yeast (and the environment). You can make some adjustments to the fermentability by changing the mash temp and a few other things also. hope that helps.

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Old 03-07-2013, 05:52 PM   #4
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TG = terminal gravity, same as FG

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Old 03-07-2013, 06:37 PM   #5
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Quote:
Originally Posted by TyTanium View Post
TG = terminal gravity, same as FG
Thx. I can see SG being starting gravity, or specifically to the word gravity here.... Specific Gravity (aka density) which is technically what we are up to. Anyhow, I see SG and think specific gravity and consider that a gravity reading not limited to the begining or end.
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Old 03-07-2013, 06:45 PM   #6
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Quote:
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Thx. I can see SG being starting gravity, or specifically to the word gravity here.... Specific Gravity (aka density) which is technically what we are up to. Anyhow, I see SG and think specific gravity and consider that a gravity reading not limited to the begining or end.
Ditto
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Old 03-07-2013, 06:52 PM   #7
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Even if you haven't take a starting gravity you can still use a gravity reading or two during the process to tell you what's going on. Your instructions should give you a starting gravity, especially if you're doing extract which is fool proof, that WILL be your gravity as long as your volume in the refermenter is what the recipe says it should be. So if you take a reading, and the number is lower that that, you know you have fermentation then.

Or you can take two over a couple days and if it's changed you know you have fermentation.

Because that is the biggest question we get on here. Is my beer fermenting, (usually followed by "because my airlock isn't or has stopped bubbling) so a number lower than the SG will tell you.

Your recipe should also tell you what the FG should be. So taking a reading if you want to know where the beer is at, will tell you how close you're getting to terminal gravity ("Hey, my airlock stopped, does that mean fermentation is done?)

If the fg for your beer is supposed to be around 1.013 and it's only been 3 days or so, and your airlock stopped, but your gravity is reading like 1.030, then more than likely fermentation is still going, but less EXCESS co2 is being produced, but fermentation is still happening.

Taking another one a day or two later will tell you if it's stuck or finished.

It's a dianostic tool. It will tell you where your beer is at and if it's stuck or finished, just by how you interpret the numbers.

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Old 03-07-2013, 11:21 PM   #8
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TG, I read a book, thats what Dave Miller called it, I kinda like it.

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Old 03-07-2013, 11:43 PM   #9
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Thanks guys good stuff, with a nice explanation

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Old 03-08-2013, 12:20 AM   #10
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I'll carry it one step further.


It also enables you to calculate apparent attenuation of your yeast and can help you select a yeast to ferment your beer.

(OG-FG)/(OG-FG). / 100 =% attenuation

This can help in diagnosing fermentation issues as well as recipe design

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