Whatis difference?

[wafflesbr0wn]

Hat is the differences between OG and SG? First batch. The instructions tell me only the OG and FG. So, what is the purpose of the SG? And, when do I inply them?

 

[AnOldUR]

OG = origianal gravity (first reading)
FG = final gravity (last reading)
SG = specific gravity (any reading you take, both the OG and FG are specific gravity readings, just taken at different times)

 

[Huisache]

Also (OG-FG)*131=ABV

 

[microbusbrewery]

SG is also used the same as OG, as in Starting Gravity.

 

[gmcastil]

Hat is the differences between OG and SG? First batch. The instructions tell me only the OG and FG. So, what is the purpose of the SG? And, when do I inply them?

Specific gravity is the density of your solution divided by the density of a reference liquid, in this case water. The reason you take gravity readings is to monitor the fermentation process.

Think of it this way. Your starting solution is sugar and H2O but no ethanol. As the yeast ferment the sugars, they produce CO2 and ethanol. Since ethanol has a lower density than water, the specific gravity of your solution decreases. Once fermentation is complete, the specific gravity stops changing and you call that reading the final gravity.

A lot of people think that fermentation is over when there are no more bubbles in their airlock - this is wrong. You can only know that fermentation is finished when several gravity readings over a couple of days remain the same.

Something else which is really important that no one has mentioned yet is that specific gravity is dependent upon temperature, so make sure that you record the temperatures of your gravity readings when you take them. Here is a link to a calculator which will correct for temperature:

http://www.brewheads.com/stats.php

Click the "Beer Statistics" link and you'll see what I mean. Hope this helps.

 

[AnOldUR]

SG is also incorrectly used the same as OG, as in Starting Gravity.

Fixed that for you.