Using refractomter to get OG?

[motobrewer]

So, I've read you can figure out the OG of a finished beer by taking a reading and doing some math.

Looks like beersmith's "Finished Beer ABV/OG" refract tool does. But it needs a hydro reading in order to calculate, is there any way to get OG without a hydro reading?

Also, I assume the finished beer sample has to be thoroughly degassed?

 

[maida7]

From what I understand, refractometers don't work on finished beer. The alcohol skews the readings.

Also, I can't see how you'd get the OG on a finished beer. Possibly if you knew the ABV. But how do you measure that?

 

[DrawTap88]

Quick search on Google turned up this chart.

Refractometers are not good at taking final gravity. Still gotta have a hydrometer for that.

 

[motobrewer]

From what I understand, refractometers don't work on finished beer. The alcohol skews the readings.

Also, I can't see how you'd get the OG on a finished beer. Possibly if you knew the ABV. But how do you measure that?

not according to Colin Kaminski :
http://byo.com/component/resource/article/1343-refractometers

It is also possible to find the starting gravity of a fermented beer. Say you have a bottle of Samuel Smith’s IPA and you are looking for the starting gravity. You can take a refractometer reading and plug the value into yet another formula. (I use ProMash to make these two calculations.)

 

[wyzazz]

More Beer has an Excel Spreadsheet that will do the math for you, you just need to take your OG with the Hydrometer. http://morebeer.com/learn_vids/vids_refract

 

[maida7]

so why are you asking the question if you already have the answer?

 

[Veinman]

A refractometer will work if you have the OG and a current refractometer reading. By plugging both into one of the many calculators ( I use BrewSmith I'm sure their are dozens online) it will give you the true FG.

 

[rico567]

Yeah, I was reading something about this....it's involved. Can't remember right now how you were supposed to figure backward, but I don't see how it could be done without an accurate OG. Me, I just use a refractometer to determine the OG, and a hydrometer to take the FG reading(s). Call me pedestrian.

 

[motobrewer]

so why are you asking the question if you already have the answer?

what? i don't have the answer.

which is why i'm asking.

 

[maida7]

what? i don't have the answer.

which is why i'm asking.

Oh in that case the answer is no.

 

[Rottnme]

Along this line...how many of you with refractometers actually use them for gravity readings after fermentation starts?

 

[Homercidal]

I took readings with both right after I got my refractometer. After calibrating with water, the refractometer was dead on with my hydrometer.

To sample the FG, I read the refractometer, and enter the number into a spreadsheet with a fairly complex formula which takes into account the alcohol. You have to have the OG to start with though. After taking readings, and running through the formula, I compared with my hydrometer, and all 3 readings so far have been exactly the same on both devices.

So, you can take FG readings with a refractometer but you have to:

1. Make sure the refractometer is calibrated each time.
2. Know your OG.
3. Enter into a formula to take the alcohol in the beer into account.

My refractometer is calibrated each time anyway. I have started putting Date, Name, and OG on a label on the fermenter. The formula is the biggest headache. I don't have Excel on my computer, so I either have to load a portable version, or use my wife's computer. I now have a droid, so I may see if there is an app that can run that formula on my phone. Or request someone to build one. And my wife's computer normally has Excel already loaded, so it's not much of a headache....

 

[bucfanmike]

you can do OG and FG with a refractometer. The trick is you MUST have the OG to make the calculation work for FG. There are numerous calculators online that do this. I use the excel sheet from morebeer. If you dont have excel, I believe that open office (freeware) will open excel spreadsheets. I tested this along with my hydrometer the first 2 times i used it and it worked well.

 

[Bobby_M]

Seems there's a breakdown of appropriate acronyms in this thread.
Specific time based measurements:
OG: original gravity (pre ferment)
FG: final (lowest) gravity (post ferment)

SG: specific gravity (general gravity measurement at ANY time, could be pre or post ferment or in between.

If you know the OG, presumably by using your refractometer, you can calculate any SG, including FG, by using your refractometer with appropriate correction formulas. It gets pretty close, but not as accurate as using a hydrometer.

 

[maida7]

Seems there's a breakdown of appropriate acronyms in this thread.
Specific time based measurements:
OG: original gravity (pre ferment)
FG: final (lowest) gravity (post ferment)

SG: specific gravity (general gravity measurement at ANY time, could be pre or post ferment or in between.

If you know the OG, presumably by using your refractometer, you can calculate any SG, including FG, by using your refractometer with appropriate correction formulas. It gets pretty close, but not as accurate as using a hydrometer.

yeah but he doesn't have the OG. He want to calculate the OG from the FG but he doesn't know the ABV and he doesn't have a hydrometer. OK?

 

[Homercidal]

yeah but he doesn't have the OG. He want to calculate the OG from the FG but he doesn't know the ABV and he doesn't have a hydrometer. OK?

He doesn't say he doesn't have the OG. He says he was told he needed a hydrometer to read FG. The answer to his questions is yes, you can use a refractometer to get FG, but you need the OG to calculate it. You can get OG from either Hydrometer, or refractometer.

The calculation compensates for the amount of alcohol produced during fermentation. To know this it has to know how much fermentable you started with. It knows where you are now. With those two things, is knows how much alcohol is in the beer, and therefore how much the alcohol is affecting the reading.

I quit using my hydrometer, because the 4 times I've used my refractometer with my hydro, I got the exact same readings for both OG and FG. As long as you are sure the refractometer is calibrated, and as long as you record or remember your OG, you CAN use a refractometer accurately for the entire process.

*Disclaimer - I know the formula that I use to calculate FG works fine. I cannot vouch for any other formula or source.

 

[maida7]

So, I've read you can figure out the OG of a finished beer by taking a reading and doing some math.

Looks like beersmith's "Finished Beer ABV/OG" refract tool does. But it needs a hydro reading in order to calculate, is there any way to get OG without a hydro reading?

Also, I assume the finished beer sample has to be thoroughly degassed?

read it again. He want to find the OG of a finished beer. Meaning the beer is fermented and he can take the FG but he doesn't have the OG or the ABV.

 

[wyzazz]

read it again. He want to find the OG of a finished beer. Meaning the beer is fermented and he can take the FG but he doesn't have the OG or the ABV.

I just assumed that the OP used the incorrect acronym, meaning he meant to say FG or SG instead of OG.

 

[motobrewer]

not according to Colin Kaminski :
http://byo.com/component/resource/article/1343-refractometers

did anyone read this before making random replies!?

It is also possible to find the starting gravity of a fermented beer. Say you have a bottle of Samuel Smith’s IPA and you are looking for the starting gravity. You can take a refractometer reading and plug the value into yet another formula. (I use ProMash to make these two calculations.)

 

[munche]

I bought a refractometer, calibrated it, and compared the FG reading to my hydrometer and it was way off, using that spreadsheet from MoreBeer.

I forgot to do it for the OG on my last beer. I'll experiment more and see how it works.