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.

thanks

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.

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.

TG = terminal gravity, same as FG

TyTanium said:

TG = terminal gravity, same as FG

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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.

ACbrewer said:

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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Ditto

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.

TG, I read a book, thats what Dave Miller called it, I kinda like it.

Thanks guys good stuff, with a nice explanation

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

duboman said:

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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Something's wrong with your equation.

Begs another question, attenuation? The amount of sugars that the yeast consumes in the wort?

duboman said:

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.

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Yes, and that's the most important thing for me to consider when thinking if a fermentation is stuck- or if it's done. If the apparent attenuation is under 65%, generally, it's stuck or there is a problem.

Just a few days ago, a guy was asking how to "unstick" his fermentation. His OG was like 1.140 and it's "stuck" at 1.060. Well, no, it's not. It's done! It's over 10% ABV currently, even though the attenuation is only about 54%. Taking the apparent attenuation, the current ABV, and the OG and FG, you can see if the beer really is stuck or not.

scrapes said:

Begs another question, attenuation? The amount of sugars that the yeast consumes in the wort?

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Yep! Apparent attenuation is the percentage of sugars the yeast consume. Real attenuation is a different measurement, which involves the ethanol in the beer.

To calculate attenuation percentage, the following equation can be used:
[(OG-FG)/(OG-1)] x 100

So using the formula you can figure what it actually is, but I'd also need the yeast FAQ to know what it should be, right?

I spent some time last night reading White Labs yeast info, it was interesting, really. I found myself looking for recipes based on the yeast I could use.

also, taking a pre-boil gravity, comparing to potential extraction will give you your mash efficiency

I know it's tempting, but a hydrometer should definitely NOT be used to check for prostate cancer...

atreid said:

I know it's tempting, but a hydrometer should definitely NOT be used to check for prostate cancer...

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That's a relief. I've been getting crazy numbers...


Finally, a confirmation that it is Friday.

freisste said:

Something's wrong with your equation.

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Oops!

Yes the bottom of the equation should be (OG-1)

scrapes said:

So using the formula you can figure what it actually is, but I'd also need the yeast FAQ to know what it should be, right?

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Yes, but if you're in a general area (70-75% for many yeast strains), then it's a good ballpark.

There are some yeast strains that are noted for low attenuation (like windsor) and some for higher attenuation (like saison yeast) but most are more in the middle.

Other factors besides strain come into play, though! Mash temperature is a huge one- you may get 80% attenuation with a 147 degree mash of some grainbills, while you may get 65% with the same strain with a 158 degree mash.

Ingredients also play a big role. Some ingredients, like simple sugars, will ferment more fully than others like dark crystal malt.

Once you get some experience with your own system, you'll see how the various factors come together to help predict attenuation.

Yooper said:

Once you get some experience with your own system, you'll see how the various factors come together to help predict attenuation.

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yes! more testing and experimentation is required!

all in the name of science, of course

It's

ADF = 100*(OE - AE)/OE

ADF = Apparent degree of fermentation
OE = Original Extract
AE = Apparent Extract.

For example a 12 °P wort fermented down to an apparent extract of 3 °P corresponds to an apparent attenuation of 100*(12 - 3)/12 = 100*9/12 = 75%. If you want to use specific gravity use just the 'points'. As 3 °P is 1.0117 SG and 12 °P is 1.0484 SG you would calculate 100*(48.4 - 11.7)/48.4 = 75.83%. This shows the slight inaccuracy incurred when SG is used instead of Plato. Note also that if you used the actual SG readings you would get
100*(1.0484 - 1.0117)/1.0484 = 3.5%

ajdelange said:

It's

ADF = 100*(OE - AE)/OE

ADF = Apparent degree of fermentation
OE = Original Extract
AE = Apparent Extract.

For example a 12 °P wort fermented down to an apparent extract of 3 °P corresponds to an apparent attenuation of 100*(12 - 3)/12 = 100*9/12 = 75%. If you want to use specific gravity use just the 'points'. As 3 °P is 1.0117 SG and 12 °P is 1.0484 SG you would calculate 100*(48.4 - 11.7)/48.4 = 75.83%. This shows the slight inaccuracy incurred when SG is used instead of Plato. Note also that if you used the actual SG readings you would get
100*(1.0484 - 1.0117)/1.0484 = 3.5%

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Right. In the final case, you need to subtract 1 from the final number in your equation. That is, divide by 0.0484, not by 1.0484. That gives the same 75.8%. So you can use actual SG, as long as you use the previously described equation (from duboman's post).