Coldbreak Brewing HERMS Giveaway!

HomeBrewSupply AMCYL Brew Kettle Giveaway!


Home Brew Forums > Home Brewing Beer > Brew Science > Does co2 affect gravity?
Reply
 
Thread Tools
Old 12-12-2011, 04:04 PM   #1
Strecker25
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2011
Location: Rochester, NY
Posts: 200
Liked 6 Times on 4 Posts
Likes Given: 1

Default Does co2 affect gravity?

Partially because I'm curious, partially because I wonder if a beer can finish its last few gravity points while under gas...does dissolved co2 affect hydrometer readings? Or could we take a hydro sample from a keg faucet the same way we would from the fermenter ( as long as no priming sugar was added)

Thanks!


Strecker25 is offline
 
Reply With Quote
Old 12-12-2011, 04:10 PM   #2
Kaz
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Amish Country, PA
Posts: 1,058
Liked 21 Times on 20 Posts
Likes Given: 7

Default

Any dissolved gas in a liquid will cause a float hydrometer to float higher. You really need to degas a sample to get an accurate gravity reading.


__________________
Draft 1: Lightly smoked Weizen
Draft 2: Belgian Wit
Draft 3: Rauchbier

Primary 1: German Scwarzbier
Primary 2:

On Deck: Belgian Brown Ale, Pale Ale, Stout
Kaz is offline
 
Reply With Quote
Old 12-12-2011, 04:17 PM   #3
Strecker25
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2011
Location: Rochester, NY
Posts: 200
Liked 6 Times on 4 Posts
Likes Given: 1

Default

Interesting, so for an exact measurement even out of the fermenter we would have to let the sample off gas for some time to rid itself of any dissolved co2? Although I would imagine the levels are so minimal that the reading may not change by very much in that scenario.
Strecker25 is offline
 
Reply With Quote
Old 12-12-2011, 09:33 PM   #4
ajdelange
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: McLean/Ogden, Virginia/Quebec
Posts: 7,763
Liked 1033 Times on 818 Posts
Likes Given: 32

Default

CO2 in the sample is a big PITA when it comes to measurement. I doesn't change the density of the solution appreciably but it screws up the reading by coming out of solution and, with a hydrometer, clinging to the side of the instrument buoying it up (making it read too high) or, in the case of a pycnometer or U-tube meter displacing liquid so that the bottle or tube contain less liquid and reads too low.

When using a hydrometer I put the sample in a cylinder, put my hand over the top and shake like mad. I then fill a second cylinder with the shaken beer (it's possible to pour off the liquid and leave the foam behind) to near the top. When the hydrometer is dropped in it causes the second cylinder to overflow carrying any remaining foam away. After the hydrometer settles, I give it a spin to dislodge any bubbles that may be adhering. This seems to work pretty well.

With a U-tube meter I suck the beer into a syringe, close the tip and shake like mad while drawing the plunger back. I then open the tip and expel the gas that was released. A few cycles of this and the beer is degassed. Anton Paar recommends feeding their instruments from a syringe, blocking the outlet of the instrument and pushing on the plunger while the measurement is being taken. The pressure holds the gas in solution. I have to believe this stiffens the U-tube (think of what happens when you blow into a balloon) but perhaps this doesn't make an appreciable difference.
ajdelange is offline
 
Reply With Quote
Old 12-16-2011, 01:06 AM   #5
maltoftheearth
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Oct 2010
Location: Carthage, North Carolina
Posts: 506
Liked 11 Times on 9 Posts
Likes Given: 20

Default

Is this problem also present for refractometers?
__________________
Brewed in 2014: Rye IPA, Honey Sage Ale, Belgian Golden Strong, California Common, Bavarian Style Lager, Weizen, Coffee Stout, Gruit, Gale Ale, Isle of Skye Golden clone, Oktoberfest, Rauchbier, Alpha Male IPA & Chocolate Pepper Stout.
maltoftheearth is offline
 
Reply With Quote
Old 12-16-2011, 03:47 AM   #6
Kaz
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Amish Country, PA
Posts: 1,058
Liked 21 Times on 20 Posts
Likes Given: 7

Default

I don't think this would affect a refractometer.
__________________
Draft 1: Lightly smoked Weizen
Draft 2: Belgian Wit
Draft 3: Rauchbier

Primary 1: German Scwarzbier
Primary 2:

On Deck: Belgian Brown Ale, Pale Ale, Stout
Kaz is offline
 
Reply With Quote
Old 12-22-2014, 01:38 AM   #7
danbronson
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2014
Posts: 5
Default

Quote:
Originally Posted by Kaz View Post
I don't think this would affect a refractometer.
I don't think so either, but alcohol definitely will.
danbronson is offline
 
Reply With Quote
Old 12-23-2014, 01:16 AM   #8
Cyclman
I Sell Koalas
HBT_LIFETIMESUPPORTER.png
Feedback Score: 1 reviews
 
Cyclman's Avatar
Recipes 
 
Join Date: Jan 2013
Location: Aurora, CO
Posts: 5,439
Liked 577 Times on 487 Posts
Likes Given: 198

Default

To the other point, you can absolutely finish a fermentation under pressure- think of the pressure at the bottom of the huge conicals at major micros.


__________________
Give a man a beer, waste an hour. Teach a man to brew, and waste a lifetime! Bill Owen quote

Why does Happy Hour limit happiness to 1/24 of the day?
Cyclman is offline
 
Reply With Quote
Reply


Thread Tools



Forum Jump

Newest Threads

LATEST SPONSOR DEALS