hydrometer question

[DaveT]

I have been pondering how exactly you are susposed to take a gravity reading.
it is susposed to be at 60*F correct?
well if I take a reading and it says 1.014 at 70* and my water is 1.000 at 70*, the water at 60* is 0.098. does this mean that I am susposed to compensate for the temperature? or just measure gravity with the wort chilled to 60*? So at 70* wich way do I compensate the 1.014 to, add or subtract .002?

hopefully I dont confuse anyone it's 4:40 am and I have had a few too manym damn home brews taste too good to stop drinking!

 

[wild]

There is a table in How To Brew at the bottom of the page called Table 18 - Hydrometer Temperature Corrections.

 

[homebrewer_99]

Yes. The calibration temp is 60F. This means you should take the temp of a sample and make it 60F.

Place your hydrometer in the sample and get a reading. It should read 1.000. If it is NOT 1.000, but 1.002, then you hydrometer is off by 2.

EDITED: This means when you take your (wort) reading and get 1.054 then it's actually 1.052 at 60F.

EDITED: Now let's say the temp of the wort is 72F. Then you would add 1 which will now be 1.053.

EDITED: Let's say your next sample reading is 1.012 at 69F. You already know you have to compensate with your -2 = 1.010. 69F is really close to 70 which CAN add 1 more making it 1.011 because it's really close.

When I brew and get my final OG numbers I automatically divide the last 2 digits by 4. This provides me with my projected FG at 75% attenuation (of the yeast). When I take my readings that's the number I am aiming for to indicate completion.

The importance of the hydrometer is to measure the success of your yeast converting the sugar in the wort to alcohol. It will also tell you if your yeast is stuck as well as when your brew is done.

Incidently, some of the numbers in the referenced chart has to be wrong:

at 32F the reading is -0.007. These are the same numbers for 46.4 and 48.2.
at 33.8 and 35.6 are -0.008 as well as 42.8 and 44.6.
at 37.4, 39.2 and 41 they are all -.0009.

 

[zoebisch01]

Just to add, some Hydrometers (it seems the newer ones??) are calibrated @68°F so be advised.

 

[FlyGuy]

Incidently, some of the numbers in the referenced chart has to be wrong:

at 32F the reading is -0.007. These are the same numbers for 46.4 and 48.2.
at 33.8 and 35.6 are -0.008 as well as 42.8 and 44.6.
at 37.4, 39.2 and 41 they are all -.0009.

Nope, that's correct. The relationship between temperature and SG is a non-linear one because the density of water is highest at about 4 degrees C / 40 degrees F.

This table *IS* wrong in the third (print) edition of John Palmer's book, however. The publisher dropped all the minus signs, for some reason.

 

[ajf]

Place your hydrometer in the sample and get a reading. It should read 1.000. If it is NOT 1.000, but 1.002, then you hydrometer is off by 2.

This means when you take your (wort) reading and get 1.054 then it's actually 1.056 at 60F

I think you mean that it's actually 1.054 at 60 F as the hydrometer is reading 0.002 high

Incidently, some of the numbers in the referenced chart has to be wrong:

at 32F the reading is -0.007. These are the same numbers for 46.4 and 48.2.
at 33.8 and 35.6 are -0.008 as well as 42.8 and 44.6.
at 37.4, 39.2 and 41 they are all -.0009.

Actually, these figures are correct, as water has a maximum density at 4C.

-a.

 

[homebrewer_99]

I'm not a real scientist though I play one in my brewery...thanks for the correction and info on H2B v3.

I concede to my distinguished neighbor to the north... :rockin:

 

[homebrewer_99]

I think you mean that it's actually 1.054 at 60 F as the hydrometer is reading 0.002 high

I edited/corrected my numbers...thanks...too early in the AM for math I guess...