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Brews & Views Bulletin Board Service * Brews and Views Archive 2009 * Archive through October 10, 2009 * Does yeast affect Specific Gravity? < Previous Next >

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Tonymaud
Member
Username: Tonymaud

Post Number: 111
Registered: 11-2008
Posted From: 151.190.254.108
Posted on Friday, September 11, 2009 - 01:06 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I took a hydrometer sample from the bottom of my primary fermenter last night when racking to secondary, which ended up having more yeast than the clearer beer I had just racked off. This made me think, does suspended yeast affect the specific gravity reading?
 

Dan Listermann
Senior Member
Username: Listermann

Post Number: 6791
Registered: 03-2004
Posted From: 74.83.191.159
Posted on Friday, September 11, 2009 - 02:42 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Theoretically yes, practically no. Remember, if the yeast is in suspension, it can't weigh much more than the beer.
 

Vance Barnes
Senior Member
Username: Vancebarnes

Post Number: 3808
Registered: 03-2003
Posted From: 69.199.10.66
Posted on Monday, September 14, 2009 - 09:44 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Specific gravity is affected by dissolved, not suspended things.
 

PaulK
Advanced Member
Username: Paulk

Post Number: 866
Registered: 02-2003
Posted From: 68.63.203.31
Posted on Tuesday, September 15, 2009 - 04:31 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

>Specific gravity is affected by dissolved, not suspended things.

Tell that to a geologist. Hydrometers are used to measure sedimentation rate of suspended soil particles in water.
 

Chris Storey
Junior Member
Username: Stuts

Post Number: 80
Registered: 07-2004
Posted From: 76.75.119.209
Posted on Tuesday, September 15, 2009 - 11:51 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I thought that too. My sample after 13 days was 1.016. The sample had a lot of bubbles in it. I let it sit until I was done kegging and it was 1.012.
 

dhacker
Senior Member
Username: Dhacker

Post Number: 1804
Registered: 11-2002
Posted From: 98.66.36.226
Posted on Tuesday, September 15, 2009 - 12:33 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I thought that too. My sample after 13 days was 1.016. The sample had a lot of bubbles in it. I let it sit until I was done kegging and it was 1.012.

Just when I think I'm understanding the science, I realize I haven't clued in on even basic things.

I've always thought bubbles (or dissolved CO2 in the hydrometer) would give you a LOWER gravity reading . . tantamount to ships sinking in the Bermuda triangle as a result of gas bubbling up from the bottom.
 

Bill Pierce
Moderator
Username: Billpierce

Post Number: 10701
Registered: 01-2002
Posted From: 24.141.103.148
Posted on Tuesday, September 15, 2009 - 12:38 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

My thoughts too, DH. There are two factors at work here. One is that suspended solids will make a liquid more buoyant; the other is that gas bubbles make it less so. Typically the effect of the latter is more pronounced in beer, but perhaps the first sample of Chris's beer was closer to a slurry than a liquid.
 

Vance Barnes
Senior Member
Username: Vancebarnes

Post Number: 3811
Registered: 03-2003
Posted From: 69.199.10.66
Posted on Tuesday, September 15, 2009 - 02:20 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I've noticed that the CO2 in a sample has 2 effects at differnt times. At first the bubbles cling to the hydrometer and make it read higher than it should. As those go away then it does read lower than it should.

I usually don't de-gas the sample when I'm going from primary to secondary. Just looking for a ballpark at that point. If I check it at kegging I'll pour it between containers to get the CO2 out before taking a reading.