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Old 02-21-2013, 10:39 PM   #1
Feb 2013
Posts: 19

Can anyone explain what OG-FG is? How I can measure it and how can I control it? I'm making my first batch ever and need some help...

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Old 02-21-2013, 10:44 PM   #2
fall-line's Avatar
Mar 2011
Seattle, WA
Posts: 435
Liked 53 Times on 36 Posts

Welcome to the forums.

OG is the "Original Gravity" of the beer.. this measures how much sugar is in the beer when you begin fermenting, before the yeast turn it into alcohol and co2.

FG is, as you would guess, "Final Graivity" which measures how much sugar remains after fermentation. You compare these numbers to see how much alcohol is in your beer, among other things.

There are a few different methods for measuring this, but the most common is a hydrometer.

It sounds like you are starting pretty much from scratch. I'd highly recommend you do some reading on the basics of brewing. How to Brew by John Palmer is a great way to start. You can even read it online. Here is the super quick, intro to brewing chapter to get you started. http://www.howtobrew.com/section1/chapter1.html

Good luck and have fun

"Brewing beer is a fun and rewarding hobby. When you do good, you get beer. When you do bad, you get beer. It's a lot like rec league softball"

Building a home brewery (and garage) from the ground up

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Old 02-21-2013, 10:50 PM   #3
Feb 2011
Milwaukee, WI
Posts: 204
Liked 31 Times on 21 Posts

Both are measures of the gravity of the wort, specifically measuring the percentage of solids (sugars) dissolved into the wort. A gravity of 1.050 equals a wort with 5% sugars dissolved into solution (plain water has a gravity of 1.000, meaning it is 100% water). You use a hydrometer to figure out the exact gravity number.

Post-fermentation your beer will then have water plus alcohol (which has a gravity slightly less than water, or less than 1.000) plus some remaining unfermented sugars.

OG is original gravity, or gravity of the wort before fermentation .

FG is final gravity, or gravity of the fermented beer.

OG minus FG will roughly correspond to the amount of alcohol in the beer (not exactly, since alcohol's gravity is less than 1, but there are online calculators to figure it. The calculation is simple but I don't know it off the top of my head)

Basically, an OG of 1.050 and a FG of 1.010 will result in about 4% alcohol.

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Old 02-21-2013, 10:52 PM   #4
Bensiff's Avatar
Mar 2008
, Washington, the state
Posts: 4,944
Liked 402 Times on 319 Posts

OG and FG stand for original gravity and final gravity and are measures of specific gravity (SG) depending on when they are taken in the process. Specific gravity is most commonly measured in homebrewing with an instrument called a hydrometer that should be included in a beginner brewers kit. You will probably need to buy a test jar in addition. Add the wort to the test jar, cool to room temperature, and then take the reading which is labeled on the hydrometer as SG for specific gravity...ie 1.050. When gravity is complete you again take another reading to determine the final gravity, ie 1.012.

What it is measuring is the specific gravity of the solution in terms of sugar. Water has a specific gravity of 1.000, when you add the sugars from the malt it increases the specific gravity. Since alcohol has a lower specific gravity than water as the yeast consume the sugar and convert it into CO2 and alcohol it decreases the specific gravity of the solution. This is how alcohol content is measured and an easy means to test for completeness of fermentation which is referred to as the apparent attenuation.

EDIT: Woohoo, looks like everyone is a faster typer than I...but, there you go, plenty of explanation.

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Old 02-21-2013, 10:58 PM   #5
Feb 2013
Posts: 19

Thanks and yeah I'm just starting to brew and will check out this link thank you guys!

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