Gravity reading

[S.R.S]

I have a coopers plastic hydrometer which came with the kit. When I 1st tested it with water it read .998 when I believe water should be 1.000?
Therefore, when the original gravity of the beer read 1.038, should I be subcontracting .002 from this reading and should I do the same from today's reading of 1.010
Brew has been in fermenting bucket for 10 days but it's not clear so don't think ready for bottling.
thanks all.

 

[bradccook]

Did you use tap water or distilled water?

 

[S.R.S]

Did you use tap water or distilled water?

tap water

 

[geoffm33]

Did you correct for the temperature of the water? The hydrometers are calibrated a a certain water temperature, like 60° or 68° for example.

Edit: .998 at 74° would be 1.00 at 60°

 

[bradccook]

You need to use distsilled water at 60°F.

 

[Nubiwan]

Does it really matter if the hydrometer is calibrated or not? Surely the ABV is calculated based in the difference between OG and FG.

Whether it is tap water, distilled water or toilet water.

Did I miss something?

 

[geoffm33]

For abv you are right. But for SG if it’s not calibrated then you won’t necesaarily get the abv you are looking for.

 

[Aggie10]

Ahhh, what?

ABV is OG - FG. Calibration accuracy issues may affect predicted ABV, but not actual. Accuracy offset will be linearly consistent.

Calibration issues also may affect dryness prediction, but again not actual. So if you get FG=1.014 but beer is dry, just adjust mentally. Or pony up a couple bucks for new hydrometer if you can't live with it.