Shelf life of wine "samples"
 

Well, I'm all ready to play with my new chemistry set. Anxious to try
out my new pH meter. Have fresh NaOH for TA. Titrets etc. Kinda
pathetic that this years batch has progressed 7-8 months before I
discover the importance of analysis.

I have time today to collect wine samples but I'll probably not get
around to the fun part of analysis for at least one week. I'm storing
(and testing) samples in wide-mouth 100ml plastic ointment pots from
the pharmacy. The seal seems water tight. I don't anticipate any
"change" in chemistry while storing samples this way. I'm I correct?
Also, is shaking the sample fairly vigorously a reasonable way to
remove CO2 pre-pH analysis?

Jim

Shelf life of wine "samples"
 

"glad heart" > wrote in message
om...
> I have time today to collect wine samples but I'll probably not get
> around to the fun part of analysis for at least one week. I'm storing
> (and testing) samples in wide-mouth 100ml plastic ointment pots from
> the pharmacy. The seal seems water tight. I don't anticipate any
> "change" in chemistry while storing samples this way. I'm I correct?

Probably.

> Also, is shaking the sample fairly vigorously a reasonable way to
> remove CO2 pre-pH analysis?

No. You need to heat it to near boiling.

Tom S

Shelf life of wine "samples"
 

If I'm testing pH, TA, and SO2 all from the same sample, is there a
"best" sequence? Eg. will microwaving sample to "near boil" change
either TA or free SO2?

Also, presumably heating a sample to test pH is only necessary
post-fermentation. Correct? I.E. a pre-fermentation must would have
no CO2.

Thanks a bunch.

Shelf life of wine "samples"
 

Hi glad heart

Heating your sample will gas off the CO2. It shouldn't affect the TA
measurement.

Frank


glad heart wrote:
> If I'm testing pH, TA, and SO2 all from the same sample, is there a
> "best" sequence? Eg. will microwaving sample to "near boil" change
> either TA or free SO2?
>
> Also, presumably heating a sample to test pH is only necessary
> post-fermentation. Correct? I.E. a pre-fermentation must would have
> no CO2.
>
> Thanks a bunch.

Shelf life of wine "samples"
 

"glad heart" > wrote in message
m...
> If I'm testing pH, TA, and SO2 all from the same sample, is there a
> "best" sequence? Eg. will microwaving sample to "near boil" change
> either TA or free SO2?

Good question. Heating will drive off free SO2 (as well as dissolved CO2),
so run free SO2 prior to heating..

You will get a different result for TA depending on whether you heat the
sample first or not. Dissolved CO2 will titrate as if it were part of the
TA and give you a false high reading.

> Also, presumably heating a sample to test pH is only necessary
> post-fermentation. Correct? I.E. a pre-fermentation must would have
> no CO2.

Correct.

Tom S

Shelf life of wine "samples"
 

> If I'm testing pH, TA, and SO2 all from the same sample, is there a
> "best" sequence? Eg. will microwaving sample to "near boil" change
> either TA or free SO2?

All tests should use separate (different) samples, except for
combining a pH reading with a titration for TA (because pH measurement
is not intrusive on the wine).

Microwaving a sample "near boiling" will potentially change your free
SO2. If you have dissolved CO2 in the sample, you will obviously
change the TA too - but that is the whole purpose in microwaving in
the first place (see below).

> Also, presumably heating a sample to test pH is only necessary
> post-fermentation. Correct? I.E. a pre-fermentation must would have
> no CO2.

It's only necessary when you have enough dissolved CO2 to change the
TA value significantly (so, no, it's not required pre-fermentation).
Heating the sample is done to drive off the CO2, so that the TA value
then obtained is representative of the fixed acidity of the sample.

Ben

Shelf life of wine "samples"
 

"Tom S" > wrote in message .com>...
>>
> You will get a different result for TA depending on whether you heat the
> sample first or not. Dissolved CO2 will titrate as if it were part of the
> TA and give you a false high reading.
>

Don't forget to add distilled water back to the original volume of the
sample before doing the pH and TA testing. If too much water is driven
off it can also give a false high reading.

Andy

Shelf life of wine "samples"
 

"JEP" > wrote in message
om...
> Don't forget to add distilled water back to the original volume of the
> sample before doing the pH and TA testing. If too much water is driven
> off it can also give a false high reading.

I forgot to mention that, but it really isn't necessary to boil the sample
that hard to drive off the dissolved CO2. If you don't boil the sample
there's no need to add water back, because none's been lost. At least not
enough to matter.

Just get it to the beginning of boiling and you're good to go.

BTW, overboiling a sample should give you a false _low_ pH.

Tom S

Shelf life of wine "samples"
 

Excellent comments everyone. Very helpful. Much obliged.