On this thread, just for kicks, let's try to prove our assumptions, or disprove them. So far all I am saying is that suspended solids (yeast) effect a hydrometer reading. It appears that the amount of effect is in relationship to the amount of suspended solids.
Where I'm headed with this. Is using a hydrometer really the benchmark when determining final gravity in a finishing/finished beer? Is it reliably more accurate than the average correction factor / refractometer software/spreadsheet/Apps?
I have wondered about this for a while. Couple'a thoughts:
1. I'm guessing that the density of yeast cells is about 0.8, so suspended yeast should effectively decrease the density of the solute allowing the hydrometer to sink further and give a false low reading. Instead of using dry yeast how about we use yeast recovered from the fermentor? Three samples.
A. Tap water.
B. Tap water plus 10 gm of yeast slurry.
C. Tap water plus 100 gm of yeast slurry.
2. In my experience refractometers are student instruments at best. Using my nice expensive (I forget which model) refractometer I was unable to reproduce a single result, so I traded it to an optimist for a beer filter (which is now for sale. lol)
You can eliminate the dissolved solids concern in a finished beer by refrigerating the sample for 6-8 hours. The yeast will lay down and play nice, and you get a nice clear sample.
Note: When I worked at the brewery I had to use Plato saccharometers, and I came to love them. So now I take all my readings in degrees Plato and translate the reading to SG (because I don't think in Plato).