what is the most accurate hydrometer reading?

I top off my all grain beers. Which is the most accurate and trustworthy hydrometer reading ... pre boil or post boil after topping off?

If you're topping off with water then your pre-boil gravity will be higher than a normal pre-boil grav. Are you not doing a full boil?

Post boil but before top off is most accurate, but you have to know how to do the math to account for your top off water if you are trying to determine your OG.

jigidyjim said:

Post boil but before top off is most accurate, but you have to know how to do the math to account for your top off water if you are trying to determine your OG.

Click to expand...

This. To clarify further, pre-top off it's going to be very concentrated wort since it's not to volume yet so the reading will be higher. After you top off, it's not a homogeneous mixture and will generally give you a lower reading. The most accurate without extra work is a reading from a full boil.

I don't think it matters as long as your measurements and math are correct.

It is very difficult to adequately mix the top-off water with the wort, and unless it is completely mixed, you will get a low gravity reading if you take the sample from the top, or a high gravity reading if you take the gravity from the bottom.
The most accurate way is to do a full boil, and not use any top-off water, as the wort is thoroughly mixed at the end of the boil.

-a.

Providing you can get the wort mixed thoroughly, the final volume in the fermenter will be the most accurate.

When you transfer from one vessel to another, you frequently leave some volume; trub, hops, etc, so while your measurement may be accurate, your volume estimate may not be.

Measuring the final volume is independent on the amount of trub, or the accuracy of the volume measurements.

You can always take a post boil pre top off reading then using a dillution calculator like the one on beersmith, input how much water you're adding and it will tell you what the gravity will be.

ok ... so I am going with post boil but before I top off ... the math is like this i think ... if i have 4 gallons @ 1.050 and I top off to 4.5 gallons I just take 4 times 50 and then devide that by 4.5 .. no? .. that would be an OG of 1.044 ... am I right with this math?

oh, and thanks for all the help on this ... it's very appreciated

And yes. You are right with your math (apart from the spelling of divide).

-a.

ajf said:

And yes. You are right with your math (apart from the spelling of divide).

-a.

Click to expand...

haha ... i was always better with math than spolling i guess ... thenks !!!