Why does my hydrometer hate me?

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belmontbrew

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This sounds too ridiculous to be true, but I think I am using my hydrometer incorrectly.

My first batch of beer measured out to about 3.5% ABV. I know that tasting alcohol is difficult and subjective, but pretty much everyone that tried it felt like it was more in the 4-5% range. I think the problem that time was that the FG sample had CO2 in it and falsely raised the gravity reading.

The second batch of beer measured 5.5% ABV. That seemed reasonable, but again, people really felt it after a pint. This was a sweet stout with 4 lbs of blueberries added. This is when I realized that CO2 might be an issue.

Third batch went into primary yesterday. This was basically all-extract, including 3 lbs of honey and 0.5 lbs of honey malt for steeping (it's the Jim Rossi Honey Pale). I measured the OG at 70F and got 1062. The expected OG was 1058. Just for kicks, I put the sample in the fridge overnight to let it settle. This morning, I took it out of the fridge and let it warm back up to 70... And I measured 1070.

So now I know that I am doing something horribly wrong. I just don't know what! Here is the procedure I am following:
1) Take sample into sampling jar (I use the spigot attached to my bucket).
2) Wait a bit to let sample settle out and reach room temperature.
3) Gently drop in hydrometer, spin it around, and let it stop bobbing.
4) Read reading.

Using this method, I seem to consistently underestimate the ABV, and I think that my OG is reading is slightly higher than actual, and that my FG reading is even more higher than actual.

Uhh... help?
 
Are you adjusting for temp? I wouldn't think it would make that extreme of a difference, but it could I guess...
 
Thanks for these suggestions!

I am correcting for temp using the sheet that came with the hydrometer, but since I'm always above 60F, the correction will always increase my gravity reading (which I suspect is too high anyway).

I've also tried it in tap water, and get eyeball-close to 1.000. Even if that was off, it shouldn't affect my ABV calculation since I would have a fixed offset for both the OG and FG readings.

I was originally thinking that my problem could be suspended particles in the sample, but I don't see how that could actually affect the reading.
 
How are you calculating your ABV? The one on the hydrometer itself isn't accurate... The true way to calculate ABV is

ABV = (OG - FG)*131
 
ALL water should be 1.00, or distilled water?

I know I'm nitpicking, but some tap water can get very hard, which could potentially throw off the SG, right?
 
Belmont, post the procedure you used to determine the ABV. As others have said you can't directly read the ABV by looking at the "potential alcohol by volume" scale on the hydrometer.
 
Seawater at 3.4% (AKA 34000 ppm) has a SG of 1.023 at 25C. That's a point per 1500 ppm, so if you have really, really hard water it will throw the scale off 0.001.
 
Is this a partial boil? If so, I'm going to go with incomplete mixing of your top-off water, so you are not getting a representative sample of your wort.
 
I'm using the formula (OG - FG)*131 = ABV.

JLem: that sounds very plausible. I am doing a partial boil, and generally wind up with 2.5 gallons of boiled wort that gets topped up to 5. I'll try mixing more before taking the sample when I do my next batch.
 
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