# Hydrometer Use

### Help Support Homebrew Talk:

#### Gilbey

##### Well-Known Member
Can someone explain exactly how use a hydrometer to determine that fermentation is complete? I thought I knew, but now I am confused!?!??!

Thanks!

Gilbey

#### uglygoat

##### Well-Known Member
the pro and con lobby will be by shortly to give you the stump speech...

basically you need to take a reading after you boil the wort. that's your original gravity... then you want to read the gravity after it's fermented (your final gravity) when your final gravity hits a specific nubmer you can be assured that fermentation is complete and you can bottle or keg.

you have to draw off a sample of the beer from your carboy and put it in a container that will allow the hydrometer to float. then you can get your reading.

i personally don't use one but that's what they are for. you can determine alcohol content as a result of the gravity readings too. you have to have the sample at a specific temp or you need to adjust the equation to get the gravity reading.

too many decimal places for this uglygoat to use a hydrometer...

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#### Gilbey

##### Well-Known Member
Thanks for the reply t1. That part I got though, I understand about OG and FG and Balling and determining alcohol content. But how can I use my hydrometer to tell that fermentation is complete if say I am not following a specific recipe and don't know the specified FG?

Am I over thinking this?

Gilbey

#### uglygoat

##### Well-Known Member
i think you are looking for a drop from your original gravity of approximately 25%... i could be wrong on the number though, i always get confused with the decimels, hence no hydrometer

#### Dark_Ale

##### Well-Known Member
Gilbey said:
Thanks for the reply t1. That part I got though, I understand about OG and FG and Balling and determining alcohol content. But how can I use my hydrometer to tell that fermentation is complete if say I am not following a specific recipe and don't know the specified FG?

Am I over thinking this?

Gilbey

Relax. Lets say you had a beer with a OG of 1.060. Then your recipe says to bottle at 1.010. You could bottle at 1.015. The only differance would be that it will be a little sweeter.(Now they say bottle too soon and you will have glass grenades, but chances are if see no activity its safe to bottle but, beware just cause you cant see anything going on does not mean the yeast are still working. So say you take your gravity reading its suppose to be 1.015 to 1.018 before bottleing. First look at your secondary see if there is any action. Next take a gravity reading say its 1.020. Just because you cant see any action does not mean in a week or two it wont make it to 1.018 or 1.015. So its been a week you take another reading if its down where it needs to be then bottle it. If its still at a 1.020 you know your not getting anywhere so at this point you could add yeast nutrient let it go another week if its still a 1.020 then you dont have much choice but to bottle it. The only time I have ran into trouble is with my big beers with a OG of 1.085.
I hope this helps I have made many mistakes and learned from all of them just becareful anything you stick into you beer make sure its sanitized. There are quite a few members who dont use hydrometers in here and if you search the threads there is a big debate on them. I use one mostly for record incase I ever want to replicate a brew. I hope this helps a little.

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#### Gilbey

##### Well-Known Member
Thanks Dark Ale. Yes your info was helpful. I will do some searching around the site. I have brewed plenty of batches without using a hydrometer, but as you suggest, I like to know for my own records.

Gilbey

#### Catullus

##### Member
Most yeast strains list a value of apparent attenuation (usually 75-85%). Attenuation = the amount of available carbon source the yeast will consume before it begins to flocculate and go dormant. This is an easy way to determine if you fermentation is complete. Say you had an OG of 1.070 and a yeast strain with apparent attenuation of 75-85%. Your fermentation would be complete when your FG stabilized with in the range of 1.0105 1.0175 any value in this range wit a 2-3 day consistent reading indicates that your fermentation is complete. Higher values indicate that you have a stuck fermentation, which could be due to unhealthy yeast, lack of nutrients, under-aeration ect

Some bacteria and wild type yeast are consider super-attenuators so lower FG values may be indicative of an infection. Hope this helps----

Jason

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#### Gilbey

##### Well-Known Member
Thank you Jason. That helps too!

Gilbey

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