"Tom S" > wrote in message
et...
>
> "Paul E. Lehmann" > wrote in message
> ...
>> Ray Calvert wrote:
>>
>>> I agree Tom. That is why I do not use a refractometer. Hydrometers are
>>> much cheaper. A refractometer is great in the field for checking grapes
>>> but even then you need to check the batch and a hydrometer is the way to
>>> go
>>> IMHO.
>>
>> If that is the case, why then, do you suppose that brix measurement is
>> the
>> standard measurement used pre-harvest and at harvest in the wine industry
>> and NOT SG?
>
> Specific gravity readings include _all_ dissolved solids, including
> whatever acids are present, and are therefore inherently inaccurate for
> measuring sugar. E.g., a juice at 23° Brix and 1.0 gram TA/100 ml will
> read 1.098 S.G. (24° Brix). Refractometers measure _only_ the sugar, so
> render a more accurate measurement.
>
> They're also a lot more convenient and rugged for field use.
>
> Tom S
>

I agree that the refractometer is definitely the way to go in the field.
Very convenient. Are you sure that it ONLY measures sugar though? We know
that alcohol has a huge effect on it which is one of the reasons it is not
used after fermentation starts. I suspect that dissolved gas has a big
effect. And I wonder if other chemicals in the juice will effect it. It
may be more accurate that a hydrometer. I am just not sure. If alcohol
effects it more that alcohol effects a hydrometer, then maybe other
chemicals effect it badly as well.

I will say it is considered bad practice in science to measure a parameter
with one tool at the start of a process and with a different tool at the end
unless the tools can be calibrated. But then you can calibrate the
hydrometer and the refractometer by measuring with both at the start and
deciding which you are going to trust. If it is the refractometer, then you
need to determine the difference and adjust the final reading in a similar
way.