Ray Calvert wrote:

>
> "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.

Unless you are a clutz like me and break them constantly.


>>>> 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.

Alcohol effects a hydrometer in a big way. That is why it is used. I am
not sure you can say that alcohol affects a refractometer more.

>
> 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.


Probably true but the following formulae developed by UC Davis (taken from
another poster a few years ago) allows one to pretty darn accurately
convert Brix to SG.

SG = (brix + 223.45) / 224.72

If you want to calculate alcohol produced you can just convert your initial
brix to SG, take your final SG reading with your hydrometer and then use
your formulae of choice to calculate alcohol produced.



> 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.