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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

Reply to
glad heart
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Probably.

No. You need to heat it to near boiling.

Tom S

Reply to
Tom S

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.

Reply to
glad heart

Hi glad heart

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

Frank

glad heart wrote:

Reply to
Frank Mirigliano

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.

Correct.

Tom S

Reply to
Tom S

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).

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

Reply to
Ben Rotter

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

Reply to
JEP

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

Reply to
Tom S

Excellent comments everyone. Very helpful. Much obliged.

Reply to
glad heart

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