Question about OG/FG readings - Home Brew Forums

Register Now!
Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > Question about OG/FG readings

Reply
 
Thread Tools
Old 06-15-2010, 08:52 PM   #1
tremorfan
Recipes 
 
Jun 2010
Houston, Texas
Posts: 17


Hey everyone, I'm definitely new to brewing (just started fermenting my second 5-gal batch), and I have a question. My first brew was a Hefeweizen, and I tried to primary in a 5-gallon PET carboy....that ended with krausen and beer all over me and my bathroom floor. When I brewed my second batch, I had about 4 gallons of wort, so instead of topping it off immediately to 5 gallons, I decided to wait 24 hours or so after pitching to let the fermentation settle down. I took an original gravity reading of the 4 gallons without thinking about it (I knew 1.061 seemed high...), but I was wondering how I can determine the actual OG if I had added the 1 gallon of water. I'm a chemical engineering student, so I know that you can't just weight the specific gravities, but if the wort is an ideal solution, you can weight the specific volumes...has anyone run into this before, or should I just stop worrying about it so much and buy a 6 gallon primary for next time?

 
Reply With Quote
Old 06-15-2010, 08:55 PM   #2
BendBrewer
 
BendBrewer's Avatar
Recipes 
 
Jan 2010
Bend, Oregon
Posts: 3,134
Liked 77 Times on 59 Posts


61 points in 4 gallons which is 61*4 = 244

244/5 = 48.8 or 1.049 (rounded up)
__________________
CarPort Brewery
JCMAC Farms Garden

 
Reply With Quote
Old 06-15-2010, 08:55 PM   #3
BendBrewer
 
BendBrewer's Avatar
Recipes 
 
Jan 2010
Bend, Oregon
Posts: 3,134
Liked 77 Times on 59 Posts


And yeah, buy a 6.5 gallon bucket.
__________________
CarPort Brewery
JCMAC Farms Garden

 
Reply With Quote
Old 06-15-2010, 08:56 PM   #4
Walker
I use secondaries. :p
HBT_LIFETIMESUPPORTER.png
 
Walker's Avatar
Recipes 
 
Sep 2005
Cary, NC
Posts: 10,987
Liked 101 Times on 89 Posts


basic averaging. water has a gravity of 1.000

4 gallons @ 1.061 + 1 gallon @ 1.000 == 5 gallons @ 1.049
__________________
Ground Fault Brewing Co.

 
Reply With Quote
Old 06-15-2010, 08:57 PM   #5
tremorfan
Recipes 
 
Jun 2010
Houston, Texas
Posts: 17

Quote:
Originally Posted by BendBrewer View Post
61 points in 4 gallons which is 61*4 = 244

244/5 = 48.8 or 1.049 (rounded up)
Thanks! I'll assume that's good enough of an estimate, haha.

 
Reply With Quote
Old 06-15-2010, 08:58 PM   #6
Walker
I use secondaries. :p
HBT_LIFETIMESUPPORTER.png
 
Walker's Avatar
Recipes 
 
Sep 2005
Cary, NC
Posts: 10,987
Liked 101 Times on 89 Posts


Quote:
Originally Posted by BendBrewer View Post
And yeah, buy a 6.5 gallon bucket.
+1 indeed.
__________________
Ground Fault Brewing Co.

 
Reply With Quote
Old 06-15-2010, 08:59 PM   #7
tremorfan
Recipes 
 
Jun 2010
Houston, Texas
Posts: 17

Quote:
Originally Posted by Walker View Post
basic averaging. water has a gravity of 1.000

4 gallons @ 1.061 + 1 gallon @ 1.000 == 5 gallons @ 1.049
yeah, i know how to average, but in my separations class, we learned that you can't just average densities without introducing significant error...you have to weight the specific volumes and adjust for unideal conditions in volume additivity...

maybe that's only relevant in industrial chemical processes?

 
Reply With Quote
Old 06-15-2010, 09:03 PM   #8
Walker
I use secondaries. :p
HBT_LIFETIMESUPPORTER.png
 
Walker's Avatar
Recipes 
 
Sep 2005
Cary, NC
Posts: 10,987
Liked 101 Times on 89 Posts


Quote:
Originally Posted by tremorfan View Post
maybe that's only relevant in industrial chemical processes?

Probably.

Basic averaging pans out just fine in our low-tech organic chemistry labs.
__________________
Ground Fault Brewing Co.

 
Reply With Quote
Old 06-15-2010, 09:04 PM   #9
mojotele
 
mojotele's Avatar
Recipes 
 
Jan 2010
Baltimore, MD
Posts: 833
Liked 18 Times on 18 Posts


I don't think that really applies here. It's not all that different from adding water to water, so the additive volume is just the result of adding the two volumes together or is so close that it is insignificant.

 
Reply With Quote
Reply
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Airlock bubbles,, gravity readings, and bottling question phishfood Beginners Beer Brewing Forum 7 03-14-2010 03:34 AM
Question regarding hitting specific OG/FG readings. febbrewro Extract Brewing 10 02-23-2010 02:20 PM
FG readings Fullerton General Techniques 6 10-22-2008 02:45 PM
Question on Saison attenuation, gravity readings and heating pads EinGutesBier General Techniques 4 05-08-2008 04:34 AM
Newb Question on Taking Hydrometer Readings Sixpack Beginners Beer Brewing Forum 10 11-16-2006 09:52 PM


Forum Jump