Hydrometer Reading Question

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Netflyer

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If I leave my hydrometer in the tube with the sample for like 15 min it seems to rise. Is it just because the temp is changing?

So I pull a sample out of 68F take an FG and I get 1.008.

After about 15-20 min, when I finished bottling the hdrometer in the tube is reading 1.012 ... I'm sure the temp went up but only to like 72-73F...

What is my real FG? :)

Thanks!
 
It may be moving due to CO2 coming out of suspension. There is more in suspension when you first pull the sample. After 15-20 min, there is less, which will give a different reading. The 4-5 degree change would'nt move your reading that much.
 
The closer the liquid line is to the top of the test tube, the easier it is to get an accurate reading. I've marked my test tube with a sharpie to give me an idea of where the liquid should come to before I drop in the hydrometer.

Try and get the hydrometer to float free of the sides of the test tube. Spinning the hydrometer before taking a reading knocks off bubbles so that the reading is more accurate.

Good Luck...
 
It's takes more shaking than you'd think to completely de-gas a sample. Bubbles are a big problem with a finish hydrometer, so I shake a sample 60 seconds and let it stand for a couple minutes.
 
Out of curiosity, how do bubbles affect the reading? On one hand, I understand the idea that, once the gas it out, you have more density, so you will theoretically get a higher gravity reading. On the other hand, if you take a reading while the sample is degassing, wouldn't that make the hydrometer more buoyant and therefore read "higher" when, in fact, it should be a lower SG?

For example, I take a hydrometer reading while I see some bubbles degassing from the sample. It reads 1.02. Since I am taking the reading during the degasssing, should I assume the SG is lower, say, 1.018 or so?
 
Good q, my FG went up after 10 min from 1.008 to 1.012 - if gas left wouldn't the hdrometer be less bouyant? Good q!

I've seen people using those Brix meters (refractometers) are they much better?
 
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